Re: [PATCH v2] arm/efi: Handle Xen bootargs from both xen.cfg and DT

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 13 Dec 2021, 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, so if the Xen configuration file is not
> specifying boot arguments, the device tree boot arguments will be
> used, if they are present.
> 
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> v2 changes:
>  - Changed logic, now xen cfg bootarg value has precedence over DT
> ---
>  docs/misc/efi.pandoc        |  4 ++++
>  xen/arch/arm/efi/efi-boot.h | 15 +++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/docs/misc/efi.pandoc b/docs/misc/efi.pandoc
> index abafb3452758..71fdc316b67b 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 the Xen configuration file value has a precedence over the DT 
> value.
>  
>  Example 1 of how to boot a true dom0less configuration:
>  
> diff --git a/xen/arch/arm/efi/efi-boot.h b/xen/arch/arm/efi/efi-boot.h
> index 4fb345f225c8..ae8627134e5a 100644
> --- a/xen/arch/arm/efi/efi-boot.h
> +++ b/xen/arch/arm/efi/efi-boot.h
> @@ -503,11 +503,26 @@ static void __init efi_arch_handle_cmdline(CHAR16 
> *image_name,
>  
>      if ( cfgfile_options )
>      {
> +        PrintMessage(L"Using bootargs from Xen configuration file.");
>          prop_len += snprintf(buf + prop_len,
>                                 EFI_PAGE_SIZE - prop_len, " %s", 
> cfgfile_options);
>          if ( prop_len >= EFI_PAGE_SIZE )
>              blexit(L"FDT string overflow");
>      }
> +    else
> +    {
> +        /* Get xen,xen-bootargs in /chosen if it is specified */
> +        const char *dt_bootargs_prop = fdt_getprop(fdt, chosen,
> +                                                   "xen,xen-bootargs", NULL);
> +        if ( dt_bootargs_prop )
> +        {
> +            PrintMessage(L"Using bootargs from device tree.");
> +            prop_len += snprintf(buf + prop_len, EFI_PAGE_SIZE - prop_len,
> +                                 " %s", dt_bootargs_prop);
> +            if ( prop_len >= EFI_PAGE_SIZE )
> +                blexit(L"FDT string overflow");
> +        }
> +    }
>  
>      if ( cmdline_options )
>      {
> -- 
> 2.17.1
>