ref-manual/variables.rst: cover FIT_LINUX_BIN variable

From: Adrian Freihofer <adrian.freihofer@siemens.com>

Document the FIT_LINUX_BIN variable used in the fit-image class to specify
the kernel binary name included in the FIT image.

Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>
---
 documentation/ref-manual/variables.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

Hi,

On Sun Oct 19, 2025 at 6:47 PM CEST, Adrian Freihofer via lists.yoctoproject.org wrote:
> From: Adrian Freihofer <adrian.freihofer@siemens.com>
>
> Document the FIT_LINUX_BIN variable used in the fit-image class to specify
> the kernel binary name included in the FIT image.

Thanks for the patch. I also sent a patch for this last week:
https://lore.kernel.org/yocto-docs/20251016-release-note-5-3-second-hunk-v1-14-20f21db1f93c@bootlin.com/

Quentin had interesting comments on it, and I think your patch more or less
matches mine, so the comments still apply. Can you have a look?

Antonin

Hi Antonin,

Sorry for not checking the queued patches before sending my patch.

Indeed, Quentin's comment is valid. FIT_LINUX_BIN refers to a file. I am confident that my patch is correct. Therefore, you are welcome to either take my patch or simply apply that single-word correction to your own. Both options are appreciated. Thank you.

Regards,
Adrian

Hi Adrian,

On 10/19/25 6:47 PM, Adrian Freihofer via lists.yoctoproject.org wrote:
> From: Adrian Freihofer <adrian.freihofer@siemens.com>
> 
> Document the FIT_LINUX_BIN variable used in the fit-image class to specify
> the kernel binary name included in the FIT image.
> 
> Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>
> ---
>   documentation/ref-manual/variables.rst | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
> index 591c03028ce..8a10dfc54e6 100644
> --- a/documentation/ref-manual/variables.rst
> +++ b/documentation/ref-manual/variables.rst
> @@ -3430,6 +3430,18 @@ system and gives an overview of their function and contents.
>         The default value is set to "x509" by the
>         :ref:`ref-classes-kernel-fit-image` class.
>   
> +   :term:`FIT_LINUX_BIN`
> +      This variable is used in the :ref:`ref-classes-kernel-fit-image` class to
> +      specify the name of the Linux kernel binary which gets included in the
> +      FIT image.

That is not true.

> +      The default value is set to "linux.bin".
> +

You have two choices. The empty string or anything not empty (including 
the default "linux.bin"). The value of the non empty string does not 
matter at all.

The wording here implies something that does not happen. It does not 
represent the name of the Linux kernel binary which gets included in the 
FIT image, it is merely sort of a boolean to decide whether to include 
linux.bin binary in the kernel FIT image.

linux.bin is generated by uboot_prep_kimage() in 
meta/classes-recipe/kernel-uboot.bbclass which is called in 
kernel_do_deploy:append() in 
meta/classes-recipe/kernel-fit-extra-artifacts.bbclass which is 
inherited whenever it is present in KERNEL_CLASSES variable. Its 
compression is stored in linux_comp file which is also read whenever 
FIT_LINUX_BIN is set. So changing FIT_LINUX_BIN logic would require a 
change for the compression field in the FIT as well.

Cheers,
Quentin