[yocto] possible to append or patch existing machine .conf file?

[Ayoub Zaki]

Hi,

On 12.10.2017 12:32, Bernd wrote:
> Suppose I have the following bugfix patch for a 3rd party machine conf
> file I am using:
>
> diff --git a/conf/machine/colibri-vf.conf b/conf/machine/colibri-vf.conf
> index 3ddef79..ba47488 100644
> --- a/conf/machine/colibri-vf.conf
> +++ b/conf/machine/colibri-vf.conf
> @@ -35,6 +35,6 @@ MKUBIFS_ARGS = " -c 8112 -e 124KiB -m 2KiB -F"
>   UBINIZE_ARGS = " -p 128KiB -m 2048 -s 2048"
>   UBI_VOLNAME = "rootfs"
>
> -SERIAL_CONSOLE ?= "115200 ttyLP0"
> +SERIAL_CONSOLE = "115200 ttyLP0"
>
>   MACHINE_FEATURES += "usbgadget usbhost vfat alsa touchscreen"
>
> Is there a proper way to somehow temporarily add something to my layer
> to apply this patch until it makes its way upstream and into the
> branch I am using? Or should I make my own machine file, include the
> original one and then change the variable?
you can add to local.conf or distro.conf :

include conf/machine/${MACHINE}-extra.conf

then create in your meta layer or bsp layer :

conf/machine/beaglebone-extra.conf
conf/machine/rasberrypi-extra.conf
conf/machine/xyz-extra.conf

which contains overrides for your machine settings.
Note that is an include and not require, which means that if you machine 
has no *extra.conf then it's simply skkiped ( no overrides)
>
> So far I have not found any elegant way to otherwise force this
> variable to its correct value in my image recipe, the only way I have
> found to work around this bug is to .bbappend the inittab recipe where
> this variable is actually used and change the value of another
> variable (SERIAL_CONSOLES, note the S at the end) which is derived
> from SERIAL_CONSOLE right there in this bbappend file. This seems to
> help.
>
> But while doing this I have also noticed a strange anomaly in the
> output of bitbake -e:
>
> * When I change the variable in my image recipe then bitbake -e will
> show another "set" access and both variables SERIAL_CONSOLE and
> SERIAL_CONSOLES will have the correct value as intended by me but the
> produced image will have the **wrong** entry in its inittab.
>
> * When I bbappend the inittab recipe to set SERIAL_CONSOLES right
> there where it is used then my final image will have a correct inittab
> and the serial console will work bit there is **no** mention of that
> variable change in the output of bitbake -e
>
> * Only when I change the machine conf file iitself to set the variable
> then bitbake -e and the produced image both show the correct entry.
> Why does it behave that way?

-- 
Ayoub Zaki
Embedded Systems Consultant

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