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



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



 


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