[yocto] RFC: Yocto BSP and kernel usability tools
Tom Zanussi
tom.zanussi at intel.com
Mon Dec 19 08:55:09 PST 2011
Hi,
This is what I hope to implement in the M2 timeframe.
Any and all comments welcome...
Thanks,
Tom
---
Getting Yocto running on a new board is often a prerequisite task to
the real task of interest for new users, which is creating new
applications designed to run on the board, or creating new
board-specific embedded systems. In other words, most users just want
to get the hardware up and running and not have to think too much
about it before moving on to what they're really interested in, which
is the stuff running on top of it.
While there really can't be any such thing as a magic-bullet
application that would do that automatically i.e. generate and
maintain a guaranteed-working Yocto BSP for any given piece of
hardware, it should at least be possible to provide a tool that would
generate a base BSP usable as a starting point for that, and which
would additionally allow the user to tweak various BSP settings,
including kernel configuration options and simple kernel patches.
Such a tool should be usable with only a minimal understanding of the
Yocto build system and metadata, and with no knowledge at all of
kernel internals or the Yocto kernel recipe bindings, or of the
details of the internals of yocto kernel repositories, or in fact any
knowledge of git or any other specific build-related tool.
This document provides the design for such a tool. At a high level,
the goal of the tool is to provide a user the means of creating a new
Yocto BSP from which it should be possible (assuming a perfect
run-time outcome, admittedly unlikely on a first pass) to submit a
'pull request' for inclusion into any repo(s) that would accept an
'official' Yocto BSP. For example, the output of the tool should
produce metadata and kernel configuration that would be directly
mergeable into the meta-intel and the linux-yocto kernel repos. The
tool should also allow the BSP maintainer to afterwards at any time
make changes to the kernel configuration and/or submit kernel patches
for the BSP.
Note that although knowledge of the Yocto kernel or kernel internals
is not expected, the user is expected to know the basics of how to
deal with the linux kernel at the 'user' level, specifically
understanding and determining the specific kernel config options
needed for the user's BSP.
Specifically, the tool will allow for the following high-level tasks,
which are discussed in more detail below:
- create a new BSP from scratch from a set of user-settable parameters
- manage individual kernel config settings
- create and use groups of kernel config settings as KERNEL_FEATUREs
- apply patches to a BSP's machine branch
The following capabilities are specifically not provided by the tool:
- help in determining a 'correct' set of kernel config options to set.
The tool assumes the user already knows that, either through diffs
of .config files before and after using 'bitbake -c menuconfig', or
some other means.
- modification of the BSP metadata after BSP creation. The tool
provides an initial 'write-once' BSP-generation capability, but
doesn't allow it to be read in and modified after the initial pass.
The user will have to make further modifications manually. The one
exception to this is kernel features, which can be added to an
already existing kernel bbappend file.
- a guarantee or even expectation that the generated BSP will work on
the actual hardware it's targeted for - it's highly unlikely the BSP
will work 'out-of-the-box' and it's the developer's reponsibility to
do the often hard work of figuring out what settings and/or code are
actually needed to get the hardware to work as expected. The goal
of the tool is to make that job easier, not to actually do that job.
Also, though it's not explicitly a requirement of this tool, the
design should be sufficiently modular to allow for its participation
in generic logical pipelines. For instance, while the tool may
present to the user a text-based UI for gathering information, it
should also be able to operate without any kind of user interaction
and retrieve the data it needs from a file, for instance e.g.:
$ yocto-bsp create < x86-input.json
Another example that the design should not preclude would be its use
at the end of a bsp-import pipeline e.g.:
$ cat 3rdparty.bsp | 3rdparty2yocto | yocto-bsp create
The tool will initially be implemented as a set of command-line tools
which will essentially be thin layers on top of a modular Python API;
future tools may be GUI-based but would make use of the functionality
exposed through the same API. There might also be an opportunity for
future integration into existing tools such as hob; this isn't
explicitly catered for in the current design, but it should be
possible to do that based either on the functionality provided by the
command-line interface or equivalently via the Python module API.
A Quick Overview
----------------
The initial set of tools will comprise 'yocto-bsp', for creating Yocto
BSPs, and 'yocto-kernel', for BSP and BSP-related Yocto kernel
maintenance tasks on existing BSPs.
The interface and detailed description of each tool are described
below, and the underlying templating mechanism is described following
that, but it would be good for context to first try to give an overall
picture of how the tools were designed to work and be used together.
The envisioned usage model is that a user would first start out by
creating a new BSP for a given architecture by invoking the 'yocto-bsp
create' command. Choosing the architecture essentially chooses a set
of files that the BSP will be based on. This set of files is a
combination of a set of 'common' files that all BSPs inherit and a set
of architecture-specific files that match the specified architecture.
Neither set of files can be used unmodified on their own as simple
static copies of the originals in order to create a working BSP for a
real machine - many of those files need to be tailored for the
hardware using information supplied by the user. To accomplish this
in an automated way, both the specific portions of the BSP files that
need to be filled in with user input, and the means of (optionally)
getting that input from the user are included as in-line annotations
to the BSP files themselves using a simple templating scheme based on
conventions used by web2py. Essentially, in the default case, the
templating system is used to generate a series of text-based prompts
that ask the user questions about the BSP being created. The data
supplied by the user is then used to fill in the missing information
in the BSP files. The user can also choose to specify all the
information needed directly to the 'yocto-bsp create' command
invocation itself; the 'yocto-bsp list' command exists to provide the
user the list of 'properties' and enumerations of possible values for
those properties, which taken together represent the data items needed
to generate the BSP. The user can even more directly supply the
information as a json object representing a serialized python
dictionary, which is what the templating interface uses natively to
represent properties and values needed for BSP generation.
The end result is a Yocto-compliant BSP that should be directly
buildable by the Yocto build system. The generated BSP is completely
self-contained - it includes not only the BSP metadata, but also the
necessary kernel components, which are normally for BSPs contained in
the linux-yocto repo's meta and machine branches for the BSP. In
order to help make the tool more efficient for the user, the tool does
everything it needs to locally by initially using the linux-yocto
SRC_URI; once ready, the user can then migrate the kernel components
to an actual linux-yocto repo by using the 'yocto-kernel migrate'
command. Once that's done, the user is in a position to submit both
the BSP metadata and the linux-yocto commits upstream.
Once a BSP is created, the job of 'yocto-bsp' is done (in the initial
version of the tools - it may have sub-commands added later that could
possibly manage the non-kernel aspects of a BSP) and the
'yocto-kernel' command can be used going forward to maintain the
kernel portion of a BSP. 'yocto-kernel' allows both bare kernel
config items and higher-level 'kernel features' to be created, used
and removed, patches to be added to a BSP's machine branch, and the
kernel changes to a BSP migrated to a linux-yocto repo. These
have typically been difficult tasks for many users; the hope is that
'yocto-kernel' will make those tasks more manageable for everyone.
The sections below describe each tool in detail.
Following those sections is a detailed description of the templating
mechanism, useful for anyone who needs to create templates for
creating new BSPs using the 'yocto-bsp create' tool.
The top-level bsp-creation tool, 'yocto-bsp'
============================================
All of the functionality of the Yocto bsp-creation tool is available
via the single 'yocto-bsp' command. Access to the specific functions
provided by the tool is accomplished by specifying sub-commands to the
main 'yocto-bsp' command. The design of the command-line interface is
based on similar interfaces provided by git and perf, which is
familiar to many users and is easily extensible.
Usage help is always available for the command itself as well as for
all sub-commands. Executing the top-level command displays a list of
the available sub-commands, with descriptions:
$ yocto-bsp
usage: yocto-bsp [--version] [--help] COMMAND [ARGS]
The most commonly used 'yocto-bsp' commands are:
create Create a new Yocto BSP
list List available values for options and BSP properties
See 'yocto-bsp help COMMAND' for more information on a specific command.
'yocto-bsp create' - Create a new Yocto BSP
-------------------------------------------
NAME
yocto-bsp-create - Create a new Yocto BSP
SYNOPSIS
yocto-bsp create <bsp-name> <karch> <kmachine>
[--property <NAME:VAL> | -p <NAME:VAL>]
DESCRIPTION
This command creates a Yocto BSP based on the specified
parameters. The new BSP will be a new Yocto BSP layer contained
within the top-level directory specified as bsp-name i.e. not
'meta-bsp-name'. The value of the 'karch' parameter determines
the set of files that will be generated for the BSP, along with
the specific set of 'properties' that will be used to fill out the
BSP-specific portions of the BSP.
The BSP-specific properties that define the values that will be
used to generate a particular BSP can be specified on the
comman-line using the --property option for each property, which
is a colon-separated name:value pair.
The set of properties and enumerations of their possible values
can be displayed using the 'yocto-bsp list' command.
It isn't necessary however for the user to explicitly specify the
property values using --property options - if none are specified
in the 'yocto-bsp create' invocation, the user will be
interactively prompted for each of the required property values,
which will then be used as values for BSP generation.
The 'kmachine' parameter names the 'machine branch' that the BSP's
machine branch will be based on; the list of branches meaningful
for that purpose can also be listed using the 'yocto-bsp list'
command.
The 'yocto-bsp list' command can also be used to list the possible
values for the 'karch' parameter.
An typical example that would query the user for property values
would be:
$ yocto-bsp create meta-foo i386 yocto/standard/common-pc/foo
Because the user hasn't specified any values for the BSP
properties, yocto-bsp will query the user for each of the
unspecified property values required to create the BSP i.e. the
properties listed by 'yocto-bsp list properties'.
Here's an example using explicitly-specified properties:
$ yocto-bsp create meta-foo i386 yocto/standard/common-pc/foo
--property tunefile:tune-atom --property touchscreen:true
--property kfeature:cfg/smp [...]
'yocto-bsp list' - List available values for options and BSP properties
-----------------------------------------------------------------------
NAME
yocto-bsp-list - List available values for options and BSP properties
SYNOPSIS
yocto bsp list <karch | kmachine>
yocto bsp list <karch> properties
yocto bsp list <karch> property <xxx>
DESCRIPTION
This command enumerates the complete set of possible values for a
specified option or property needed by the BSP creation process.
The first form enumerates all the possible values that exist and
can be specified for the 'karch' or 'kmachine' parameters to the
'yocto bsp create' command. Example output for those options:
$ yocto-bsp list karch
i386
x86_64
arm
powerpc
mips
$ yocto-bsp list kmachine
yocto
yocto/standard
yocto/standard/common-pc
yocto/standard/common-pc-64
yocto/standard/preempt-rt
The second form enumerates all the possible properties that exist
and must have values specified for them in the 'yocto bsp create'
command for the given 'karch'. Example output for that command:
$ yocto-bsp list i386 properties
"machine": boolean,
"kmachine": choice,
"tunefile": choicelist,
"smp": boolean,
"xserver": choicelist
["xserver-choice": choice]
"kfeatures": choicelist
["kfeature": choice]
"touchscreen": boolean,
"keyboard": boolean
The third form enumerates all the possible values that exist and
can be specified for any of the enumerable properties of the given
'karch' in the 'yocto bsp create' command. Example output for
those properties:
$ yocto-bsp list i386 property xserver
xserver-vesa
xserver-i915
xserver-emgd
$ yocto-bsp list i386 property kfeatures
features/taskstats
cfg/sound
$ yocto-bsp list i386 property tunefile
i386
tune-atom
tune-core2
$ yocto-bsp list x86_64 property tunefile
x86_64
tune-x86_64
tune-corei7
tune-ivb
$ yocto-bsp list powerpc property tunefile
powerpc
tune-ppc603e
tune-ppce300c2
tune-ppce500
tune-ppce500mc
tune-ppce500v2
tune-ppce5500-32b
tune-ppce5500-64b
$ yocto-bsp list arm property tunefile
arm
tune-arm1136jf-s
tune-arm920t
tune-arm926ejs
tune-arm9tdmi
tune-armv7
$ yocto-bsp list mips property tunefile
mips
tune-mips32
The top-level kernel usability tool, 'yocto-kernel'
===================================================
All of the functionality of the Yocto kernel usability tool is
available via the single 'yocto-kernel' command. Access to the
specific functions provided by the tool is accomplished by specifying
sub-commands to the main 'yocto-kernel' command. The design of the
command-line interface is based on similar interfaces provided by git
and perf, which is familiar to many users and is easily extensible.
Usage help is always available for the command itself as well as for
all sub-commands. Executing the top-level command displays a list of
the available sub-commands, with descriptions:
$ yocto-kernel
usage: yocto-kernel [--version] [--help] COMMAND [ARGS]
The most commonly used 'yocto-kernel' commands are:
feature-list List available Yocto KERNEL_FEATUREs
feature-define Define a new Yocto KERNEL_FEATURE
feature-add Add Yocto KERNEL_FEATUREs to a BSP
feature-rm Remove Yocto KERNEL_FEATUREs from a BSP
config-list List the modifiable set of bare kernel config options for a BSP
config-add Add or modify bare kernel config options for a BSP
config-rm Remove bare kernel config options from a BSP
patch-add Patch the Yocto kernel for a specific BSP
migrate Move local kernel config/patches to a git repo
See 'yocto-kernel help COMMAND' for more information on a specific command.
'yocto-kernel feature list' - List available Yocto KERNEL_FEATUREs
------------------------------------------------------------------
NAME
yocto-kernel-feature-list - List available Yocto KERNEL_FEATUREs
SYNOPSIS
yocto-kernel feature list <bsp-name> --used
DESCRIPTION
This command lists all the kernel features available to a BSP.
This includes any features temporarily attached to the named BSP
via the 'feature define' command and thus the reason this command
takes bsp-name as a parameter.
If the --used param is specified, only the KERNEL_FEATURES used by
the BSP are listed.
'yocto-kernel feature define' - Define a new Yocto KERNEL_FEATURE
-----------------------------------------------------------------
NAME
yocto-kernel-feature-define - Define a new Yocto KERNEL_FEATURE
SYNOPSIS
yocto-kernel feature define <bsp-name> <feature-name> <feature-desc>
[<CONFIG_XXX=x> ...] [--dirname <dirname>] [--policy <hw|non-hw>]
DESCRIPTION
This command defines a new kernel feature, resulting in the
addition of two new files for feature xxx to the named BSP's
SRC_URI. If dirname is specified, the feature files will be named
features_dirname_xxx.cfg and features_dirname_xxx.scc. Otherwise,
the features will be named cfg_xxx.cfg and cfg_xxx.scc. The idea
behind the naming is that the names reflect the user's intent to
have the feature migrated to either the kernel-cache/cfg or
kernel-cache/features directory if/when the kernel portion of the
BSP is migrated into the linux-yocto kernel repo.
The policy stating whether the new feature is considered to be a
hardware or a non-hardware feature also needs to be specified in
order to create a new feature, and a description of the new
feature is also required; this will be added as a comment to the
.scc file.
NOTE: Although features are not BSP-specific, until the user has
gone through the steps of migrating a feature to the linux-yocto
repo, it needs to live somewhere accessible to the BSP metadata,
which logically would be the kernel SRC_URI for the BSP using it.
NOTE: It's up to the user to determine whether or not the config
options for a feature being added make sense or not - this command
does no sanity checking or verification of any kind to ensure that
the config options contained in a kernel feature really make sense
and will actually be set in in the final config. For example, if
a config option depends on other config options, it will be turned
off by kconfig if the other options aren't set correctly.
'yocto-kernel feature add' - Add Yocto KERNEL_FEATUREs to a BSP
---------------------------------------------------------------
NAME
yocto-kernel-feature-add - Add Yocto KERNEL_FEATUREs to a BSP
SYNOPSIS
yocto-kernel feature add <bsp-name> [<FEATURE> ...]
DESCRIPTION
This command adds one or more kernel features to a BSP. The set
of features available to be added by this command for a BSP can be
found via the 'yocto-kernel feature list' command. This command
essentially adds a new machine-specific KERNEL_FEATURE_append to
the linux-yocto .bbappend for the BSP.
'yocto-kernel feature rm' - Remove Yocto KERNEL_FEATUREs from a BSP
-------------------------------------------------------------------
NAME
yocto-kernel-feature-rm - Remove Yocto KERNEL_FEATUREs from a BSP
SYNOPSIS
yocto-kernel feature rm <bsp-name> [<FEATURE> ...]
DESCRIPTION
This command removes one or more kernel features from a BSP. The
set of features available to be removed by this command for a BSP
can be found via the 'yocto-kernel feature list' command, if the
--used option to that command is specified. This command
essentially removes a machine-specific KERNEL_FEATURE from the
linux-yocto .bbappend for the BSP.
'yocto-kernel config list' - List a BSP's modifiable config options
-------------------------------------------------------------------
NAME
yocto-kernel-config-list - List the modifiable set of bare kernel
config options for a BSP
SYNOPSIS
yocto-kernel config list <bsp-name>
DESCRIPTION
This command lists the 'modifiable' config items for a BSP
i.e. the items which are eligible for modification or removal by
other yocto-kernel commands.
'modifiable' config items are the config items contained a BSP's
foo.cfg base config.
'yocto-kernel config add' - Add or modify a BSP's kernel config options
-----------------------------------------------------------------------
NAME
yocto-kernel-config-add - Add or modify bare kernel config options
for a BSP
SYNOPSIS
yocto-kernel config add <bsp-name> [<CONFIG_XXX=x> ...]
DESCRIPTION
This command adds one or more CONFIG_XXX=x items to a BSP's
foo.cfg base config. If a config item is already present, the new
value will simply overwrite the old value.
NOTE: It's up to the user to determine whether or not the config
options being added make sense or not - this command does no
sanity checking or verification of any kind to ensure that a
config option really makes sense and will actually be set in in
the final config. For example, if a config option depends on
other config options, it will be turned off by kconfig if the
other options aren't set correctly.
'yocto-kernel config rm' - Remove BSP kernel config options
-----------------------------------------------------------
NAME
yocto-kernel-config-rm - Remove bare kernel config options from a
BSP
SYNOPSIS
yocto-kernel config rm <bsp-name> [<CONFIG_XXX> ...]
DESCRIPTION
This command removes (turns off) one or more CONFIG_XXX items to a
BSP's foo.cfg base config.
The set of config items available to be removed by this command
for a BSP can be found via the 'yocto-kernel config list'
command.
'yocto-kernel patch add' - Patch the Yocto kernel for a specific BSP
--------------------------------------------------------------------
NAME
yocto-kernel-patch-add - Patch the Yocto kernel for a specific BSP
SYNOPSIS
yocto-kernel patch add <bsp-name> [<PATCH> ...]
DESCRIPTION
This command adds one or more patches to a BSP's machine branch.
The patch will be added to the BSP's linux-yocto kernel SRC_URI
and will be guaranteed to be applied in the order specified.
NOTE: It's up to the user to determine whether or not the patches
being added makes sense or not - this command does no sanity
checking or verification of any kind to ensure that a patch can
actually be applied to the BSP's kernel branch; it's assumed that
the user has already done that.
'yocto-kernel migrate' - Move local kernel config/patches to a git repo
-----------------------------------------------------------------------
NAME
yocto-kernel-migrate - Move local kernel config/patches to a git repo
SYNOPSIS
yocto-kernel migrate <bsp-name> <local linux-yocto repo>
DESCRIPTION
This command converts the kernel configuration changes, patches,
and features collected in a BSP's linux-yocto SRC_URI into an
equivalent set of commits in a local linux-yocto repo. On
success, the local files will named in the SRC_URI will be
removed, and the linux-yocto .bbappend will be fixed up to point
to the new repo.
NOTE: The user is responsible for submitting the generated commits
upstream and subsequently modifying the kernel .bbappend to
use the upsteam kernel repo.
The design of the 'yocto-bsp create' templating mechanism
==========================================================
This section describes the details of the templating mechanism used by
'yocto-bsp' to generate BSPs.
Generating a new BSP is basically a templating exercise. A given BSP
is comprised of a combination of a set of common files that all BSPs
share along with a set of files specific to a given BSP type. Many of
the files in both sets need to be configured according to the needs of
the BSP; this also extends to the naming and existence of the files
themselves.
The templating scheme used in the Yocto tool is partly inspired by
ideas from web2py, but adapted to a more general input mechanism for
the specific problems posed by Yocto.
There are no special files, just marked-up BSP metadata and kernel
configuration, .scc, and patch files.
The Yocto BSP markup is meant to be extremely simple and limited to
pretty much this initial set of items; it is however designed to be
extensible enough to cover any future need.
Anything within double braces is considered to be a Yocto BSP markup
tag:
{{ foo }}
Anything within double braces and starting with {{= is considered to
implement simple variable replacement, where variables are by default
simply keys in a dictionary representing the BSP and containing values
for the whole BSP:
{{=machine}}
The above means that the whole expression will be replaced with the
value of the 'machine' entry in the BSP dictionary. The syntax is
actually shorthand for the equivalent Python code for accessing the
value of a given key, but isn't restricted to that e.g. it could
reference a local variable defined in a previous tag, for instance.
In every other case, the 'yocto-bsp' tool will pre-process the
contents looking for certain keywords at the beginning. The rest it
will treat as Python code. As of now, there's only one keyword that's
meaningful:
{{ input }}
which signals that anything contained is input-related. The
'yocto-bsp' implementation will use this information to prompt the
user for input. Under certain conditions e.g. when the user has
already supplied this information via a file for instance, anything
contained in this is considered a no-op and ignored.
Anything else is considered to be Python code and will be directly
incorporated into the BSP generation code.
{{ if keyboard == False: }}
Note also that any of the above can also be used in file and directory
names, which will also be processed in the same way; this allows us to
avoid extraneous files is consistent with the rest of the scheme.
Internally, the way things are envisioned to work is that the tool
will first read in the set of files that makes up the BSP for the
chosen architecture. It will then pre-process all the 'input' tags it
finds and use that to prepare a series of text-based prompts to
retrieve the needed information from the user. The end result of
presenting all that to the user will be a completd BSP dictionary
containing all the key/value pairs needed to fill in the BSP. Once
that information is available, it will make a second pass over the
remaining tags and fill them in with the Python code needed to
retrieve and replace the remaining tags with their corresponding
values from the BSP dictionary (or any other source possibly
introduced by other tags). The end result of this second pass will be
executed as Python code to produce the final BSP metadata.
For the first version, the 'input' tags will be used to construct a
series of text-based questions for the user. The design, however,
should make it relatively trivial to create an application that could
create real GUI that would do the same thing at some later point. For
example, such an application could use the input tags to generate a
web-based form, which would return the results gathered from the user
to a web service in the form of a json blob that could directly be
converted into the BSP Python dictionary needed. e.g. the browser
would return something like this to the web service, which would in
turn send it to the 'bsp-create' library function to create the final
BSP.
{
"machine": "foo",
"kmachine": "/yocto/standard/base",
"tunefile": "tune-atom",
"smp": true,
"xserver": {
"xserver-choice": "xserver-i915",
},
"kfeatures": [
"kfeature": "features/taskstats",
"kfeature": "cfg/sound",
]
},
touchscreen: false,
keyboard: true
}
Below are some concrete examples of specific tags and how they're used.
Here's a simple example of markup that describes information needed
from the user about touchscreen and keyboard capabilities in the
formfactor 'machconfig' file:
# Assume a USB mouse and keyboard are connected
{{ input type:"boolean" name:"touchscreen" msg:"Does your BSP have a touchscreen?" }}
HAVE_TOUCHSCREEN={{=touchscreen}}
{{ input type:"boolean" name:"keyboard" msg:"Does your BSP have a keyboard?" }}
HAVE_KEYBOARD={{=keyboard}}
For instance, the touchscreen 'input' tag above describes everything a
UI would need in order to retrieve an answer from the user as to
whether the hardware in question has a touchscreen or not.
The 'type' key comprises a small set of possible input types that
include things like 'boolean' (yes/no) choices and lists of choices
(type:"choicelist").
The 'name' key provides a means for later markup to access the value
of the variable containing the user's answer for that input. For
example, the name:"touchscreen" simply references the value in the BSP
dictionary that was filled in with the user's response to the question
which was formed and presented to the user using the "msg" tag in the
input tag.
Below the input tag is the actual content that will be rendered into
the 'machconfig' file, but with the {{=}} portion replaced with the
'touchscreen' value supplied by the user i.e.:
HAVE_TOUCHSCREEN={{=touchscreen}}
will be rendered as:
HAVE_TOUCHSCREEN=0
Assuming the user answered 'no'.
Another interesting thing to note about this example is that in Yocto
BSPs, the machconfig files are contained within a filesystem location
that includes the machine name in the path e.g.
recipes-bsp/formfactor/formfactor/foo/machconfig
To accomplish this, the directory names themselves contain markup that
gets processed and replaced by the tool:
recipes-bsp/formfactor/formfactor/{{=machine}}/machconfig
Here, the {{=machine} directory is renamed to /foo to match the
machine name of the BSP.
Here's a more involved example, markup included in the
i386/conf/{{=machine}}.conf file:
{{ input type:"boolean" name:"xserver" msg:"Do you need support for X?" }}
{{ if xserver: }}
XSERVER ?= "${XSERVER_IA32_BASE} \
${XSERVER_IA32_EXT} \
{{ input type:"choicelist" name:"xserver_choice" msg:"Please select an xserver for this machine" }}
{{ input type:"choice" val:"xserver-vesa" msg:"VESA xserver support" }}
${XSERVER_IA32_VESA} \
{{ input type:"choice" val:"xserver-emgd" msg:"EMGD xserver support (proprietary)" }}
${XSERVER_IA32_EMGD} \
{{ input type:"choice" val:"xserver-i915" desc:"i915 xserver support" }}
${XSERVER_IA32_I915} \
"
In this case, we start off with a boolean 'input' question asking if
the BSP needs to support X. The following line is straight Python
code which essentially skips the following sections (until a blank
line) if the user's answer was 'no', or if the answer was 'yes',
creates a further query to the user asking which xserver type to use.
In the latter case, the input type is a list of choices resulting in
the values specified by the 'val' tag appearing as the value for the
'xserver_choice' dictionary key.
Code further down in the .conf file can also make use of this
information to include or exclude content based on the value of the
xserver_choice variable:
{{ if xserver_choice == "xserver-emgd": }}
PREFERRED_VERSION_xserver-xorg ?= "1.9.3"
PREFERRED_VERSION_mesa-dri ?= "7.11"
PREFERRED_VERSION_emgd-driver-bin ?= "1.8"
{{ if xserver_choice == "xserver-vesa" or xserver_choice == "xserver-emgd": }}
APPEND += "video=vesafb vga=0x318"
Note again that the tags used to determine whether or not to include
content simply contain Python code used to directly implement the
needed logic. Not only is there no need for the user to learn a
special-purpose language, but gives the tool the flexibility to add
essentially any kind of processing logic needed in the future.
In the case of xserver choices, we also need to use the value of
xserver_choice to determine which xorg.conf file to add to the BSP.
Again, consistent with the rest of the markup processing, this is
seamlessly accomplished by adding markup to the filenames themselves:
recipes-graphics/xserver-xf86-config/{{=machine}}/{{ if xserver_choice == xserver_emgd: }} xorg.conf
recipes-graphics/xserver-xf86-config/{{=machine}}/{{ if xserver_choice == xserver_vesa: }} xorg.conf
recipes-graphics/xserver-xf86-config/{{=machine}}/{{ if xserver_choice == xserver_i915: }} xorg.conf
In this case, the filenames actually contain Python code that
describes the conditions needed to include those particular files.
Here's another example, again making use of general-purpose Python in
the markup to generate an open-ended list of choices for the user, in
this case in linux-yocto_3.0.bbappend, to generate a list of available
KERNEL_FEATURES for the user to choose from:
{{ input type:"checklist" name:"kfeatures" gen:"fetch-kernel-features()" msg:"Please choose the kernel features to use in this BSP on" }}
{{ for kfeature in kfeatures: }}
KERNEL_FEATURES_append_{{=machine}} += {{=kfeature}}
In this case an 'input' tag calls an internally-defined yocto-bsp
function named fetch_kernel_feature() that generates the list of
available KERNEL_FEATURES. The output of that call is a Python list
containing the features, which is assigned to the 'kfeatures'
variable. The next tag contains Python code that simply iterates over
that list, and uses the value of the current feature, 'kfeature', to
append the chosen kernel features to the list of features used by the
BSP.
Finally, because the kernel components are actually part of the BSP
metadata, the user-specified values are also available in the
processing of those files. For instance, in the below case, we can
use the xserver_choice to include or exclude specific kernel
configuration settings in the
recipes-kernel/linux/linux-yocto/{{=machine}}.scc file associated with
the BSP:
{{ if xserver_choice == "xserver-emgd": }}
include features/drm-emgd/drm-emgd.scc
---
For reference, here's an example of how the tools are expected to be
laid out. Everything is contained within a 'bsp-tools' directory
under '/scripts'. The 'common' portion, containing the files common
to every BSP are:
bsp-tools/
bsp-tools/yocto-bsp.py
bsp-tools/yocto-kernel.py
bsp-tools/bsp-cache
bsp-tools/bsp-cache/target
bsp-tools/bsp-cache/target/arch
bsp-tools/bsp-cache/target/arch/common
bsp-tools/bsp-cache/target/arch/common/README.sources
bsp-tools/bsp-cache/target/arch/common/binary
bsp-tools/bsp-cache/target/arch/common/binary/.gitignore
bsp-tools/bsp-cache/target/arch/common/recipes-kernel
bsp-tools/bsp-cache/target/arch/common/recipes-kernel/linux
bsp-tools/bsp-cache/target/arch/common/COPYING.MIT
bsp-tools/bsp-cache/target/arch/common/README
bsp-tools/bsp-cache/target/arch/common/recipes-graphics
bsp-tools/bsp-cache/target/arch/common/recipes-graphics/xorg-xserver
bsp-tools/bsp-cache/target/arch/common/recipes-graphics/xorg-xserver/{{ if xserver: }} xserver-xf86-config_0.1.bbappend
bsp-tools/bsp-cache/target/arch/common/conf
bsp-tools/bsp-cache/target/arch/common/conf/layer.conf
bsp-tools/bsp-cache/target/arch/common/recipes-core
bsp-tools/bsp-cache/target/arch/common/recipes-core/tasks
bsp-tools/bsp-cache/target/arch/common/recipes-core/tasks/task-core-tools.bbappend
bsp-tools/bsp-cache/target/arch/common/recipes-bsp
bsp-tools/bsp-cache/target/arch/common/recipes-bsp/formfactor
bsp-tools/bsp-cache/target/arch/common/recipes-bsp/formfactor/formfactor_0.0.bbappend
bsp-tools/bsp-cache/target/arch/common/recipes-bsp/formfactor/formfactor
bsp-tools/bsp-cache/target/arch/common/recipes-bsp/formfactor/formfactor/{{=machine}}
bsp-tools/bsp-cache/target/arch/common/recipes-bsp/formfactor/formfactor/{{=machine}}/machconfig
The BSP-specific files are contained in directories named for the
architecture. In this case, only the i386 files are expanded as an
example.
bsp-tools/bsp-cache/target/arch/arm
bsp-tools/bsp-cache/target/arch/powerpc
bsp-tools/bsp-cache/target/arch/i386
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto-rt_3.0.bbappend
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto_3.0.bbappend
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto/{{=machine}}.cfg
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto/{{=machine}}.scc
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto/{{=machine}}-preempt-rt.scc
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto/{{=machine}}-standard.scc
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto-rt
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto-rt/{{=machine}}.cfg
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto-rt/{{=machine}}.scc
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto-rt/{{=machine}}-preempt-rt.scc
bsp-tools/bsp-cache/target/arch/i386/recipes-kernel/linux/linux-yocto-rt/{{=machine}}-standard.scc
bsp-tools/bsp-cache/target/arch/i386/recipes-graphics
bsp-tools/bsp-cache/target/arch/i386/recipes-graphics/xserver-xf86-config
bsp-tools/bsp-cache/target/arch/i386/recipes-graphics/xserver-xf86-config/{{=machine}}
bsp-tools/bsp-cache/target/arch/i386/recipes-graphics/xserver-xf86-config/{{=machine}}/{{ if xserver-choice == xserver-emgd: }} xorg.conf
bsp-tools/bsp-cache/target/arch/i386/recipes-graphics/xserver-xf86-config/{{=machine}}/{{ if xserver-choice == xserver-vesa: }} xorg.conf
bsp-tools/bsp-cache/target/arch/i386/recipes-graphics/xserver-xf86-config/{{=machine}}/{{ if xserver-choice == xserver-i915: }} xorg.conf
bsp-tools/bsp-cache/target/arch/i386/conf
bsp-tools/bsp-cache/target/arch/i386/conf/machine
bsp-tools/bsp-cache/target/arch/i386/conf/machine/{{=machine}}.conf
bsp-tools/bsp-cache/target/arch/mips
bsp-tools/bsp-cache/target/arch/x86_64
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