Re: [PATCH] arm/efi: Handle Xen bootargs from both xen.cfg and DT

[Julien Grall <julien@xxxxxxx>]

Hi Luca,

On 06/12/2021 15:36, Luca Fancellu wrote:
> Currently the Xen UEFI stub can accept Xen boot arguments from
> the Xen configuration file using the "options=" keyword, but also
> directly from the device tree specifying xen,xen-bootargs
> property.
>
> When the configuration file is used, device tree boot arguments
> are ignored and overwritten even if the keyword "options=" is
> not used.
>
> This patch handle this case, if xen,xen-bootargs is found in the
> device tree, it is used for xen boot arguments regardless they
> are specified in the Xen configuration file or not.
>
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> ---
>   docs/misc/efi.pandoc        | 4 ++++
>   xen/arch/arm/efi/efi-boot.h | 7 +++++++
>   2 files changed, 11 insertions(+)
>
> diff --git a/docs/misc/efi.pandoc b/docs/misc/efi.pandoc
> index abafb3452758..b7d99de87f15 100644
> --- a/docs/misc/efi.pandoc
> +++ b/docs/misc/efi.pandoc
> @@ -249,6 +249,10 @@ UEFI stub for module loading.
>   When adding DomU modules to device tree, also add the property
>   xen,uefi-cfg-load under chosen for Xen to load the Xen config file.
>   Otherwise, Xen will skip the config file and rely on device tree alone.
> +When using the Xen configuration file in conjunction with the device tree, you
> +can specify the Xen boot arguments in the configuration file with the 
> "options="
> +keyword or in the device tree with the "xen,xen-bootargs" property, but be
> +aware that a device tree value has a precedence over the configuration file.
I am not sure I agree with the precedence chosen here. With UEFI 
environment it is a lot easier to update the configuration file over the 
Device-Tree. So this could be used to quickly test a command line before 
updating the Device-Tree.
Also, somewhat unrelated to this patch. Looking at the code, the command 
line is a concatenation of "options=" from the configuration file and 
the extra arguments provided on the command line used to execute the 
UEFI binary.
When using the command line from the Device-Tree, I think it would still 
make sense to append the later because it could allow a user to provide 
a single Device-Tree with extra options on the UEFI command line.
But I think this is a separate subject. So if we are going to go with 
the precedence you suggested, then we should at least clarify in the 
documentation that it will replace both.
Cheers,

--
Julien Grall