[meta-intel] [PATCH 1/1] README: Documentation of hardware features

[Tom Zanussi]

On Thu, 2014-10-02 at 14:14 -0700, nitin.a.kamble at intel.com wrote:
> From: Nitin A Kamble <nitin.a.kamble at intel.com>
> 
> Starting a new documentation section to describe the layer specific hardware
> features. At this point the intel-ucode machine feature is described here.
> In the future more such features will be described in this section.
> 
> Signed-off-by: Nitin A Kamble <nitin.a.kamble at intel.com>
> ---
>  README | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 75 insertions(+)
> 
> diff --git a/README b/README
> index c829fdb..f633f36 100644
> --- a/README
> +++ b/README
> @@ -83,3 +83,78 @@ The meta-intel maintainers will do their best to review and/or pull in
>  a patch or patchset within 24 hours of the time it was posted.  For
>  larger and/or more involved patches and patchsets, the review process
>  may take longer.
> +
> +
> +Machine Features in the meta-intel layer
> +========================================
> +
> +Many machine features are available in the oecore/poky layer for BSP use.
> +The meta-intel layer makes some additional machine features available for BSPs
> +using the meta-intel layer.
> +
> +Requirements
> +------------
> +
> +The additional machine features are only available when the meta-intel layer
> +is included in the build config, and the meta-intel.inc file is included in
> +the machine configuration of the interested BSP.
> +
> +To make these features available for your machine, you will need to:
> +
> +1. have a configuration line as seen below in the bblayers.conf
> +	BBLAYERS += "<local path>/meta-intel.git"
> +2. have the following line in the machine configuration
> +	require conf/machine/include/meta-intel.inc
> +
> +Once the above requirements are met, then the machine features provided by
> +the meta-intel layer will be available for the BSP use.
> +
> +Available Machine Features
> +--------------------------
> +
> +As of now the meta-intel layer provides the following list of machine features.
> +In the future, more machine features may be available in this list.
> +
> +* intel-ucode
> +
> +These machine features can be included by listing them in the MACHINE_FEATURES
> +variable in the machine configuration file.
> +
> +Details of the Machine Features
> +-------------------------------
> +
> +* intel-ucode: This feature provides microcode updating support for Intel
> +  processors. With the intel-ucode feature, images get complete support for
> +  updating the microcode on Intel processors. This feature enables microcode
> +  updating at early boot time by placing the microcode data files in the
> +  initrd image. It also puts the user land microcode updating tool iucode_tool
> +  and the microcode data file in the target images.
> +
> +  Q. Why to enable this microcode feature?
> +  A. Intel releases microcode updates to correct processor behavior as
> +     documented in the respective processor specification updates. While
> +     the regular approach to getting this microcode update is via a BIOS
> +     upgrade, this can be an administrative hassle and not always possible
> +     in the field. The intel-ucode feature enables the microcode update
> +     capability from the Linux OS. It provides an easy path for upgrading
> +     processor microcode without need of changing BIOS. Once the feature
> +     is enabled, it is also possible to update the existing images with
> +     newer microcode update in the future.
> +
> +  Q. How to bundle only specific microcodes in the target image?
> +  A. The Intel microcode data file released by Intel contains microcode
> +     updates for multiple processors. If the BSP image will be running only
> +     on a certain kind of processors, then the number of microcodes bundled in
> +     the target image can be filtered by specifying the UCODE_FILTER_SIGNATURES
> +     variable. A sequence of iucode-tool parameters are listed in the
> +     UCODE_FILTER_SIGNATURES variable to filter the microcodes from the
> +     microcode data file. For more information on these parameters refer to
> +     the iucode-tool manual page, which can be seen over here:
> +       http://manned.org/iucode-tool
> +

I took a quick look at the iucode-tool manpage, but didn't see anything
describing the signatures themselves or where to find them.  It would be
helpful to the user of this feature to have some idea of where to look
to find them.  Could you perhaps add a bit about that?

Thanks,

Tom

> +  Q. When to not enable this microcode feature?
> +  A. The microcode datafile and the associated tools take small (few KB)
> +     space on the target image. The BSPs which are highly sensitive to the
> +     target image size, which are not experiencing any microcode related issues,
> +     may consider not enabling this feature to save the target image foot print.
> +