Re: [PATCH 0/2] Fix CMDLINE_EXTEND handling for FDT "bootargs"

On Mon, Mar 01, 2021 at 08:19:32AM -0600, Rob Herring wrote:

On Thu, Feb 25, 2021 at 6:59 AM Will Deacon [off-list ref] wrote:

quoted

We recently [1] enabled support for CMDLINE_EXTEND on arm64, however
when I started looking at replacing Android's out-of-tree implementation [2]

Did anyone go read the common, reworked version of all this I
referenced that supports prepend and append. Here it is again[1].
Maybe I should have been more assertive there and said 'extend' is
ambiguous.

I tried reading that, but (a) most of the series is not in the mailing list
archives and (b) the patch that _is_ doesn't touch CMDLINE_EXTEND at all.
Right now the code in mainline does the opposite of what it's documented to
do.

quoted

with the upstream version, I noticed that the two behave significantly
differently: Android follows the Kconfig help text of appending the
bootloader arguments to the kernel command line, whereas upstream appends
the kernel command line to the bootloader arguments. That is, except for
the EFI stub, which follows the documented behaviour.

I think the documented behaviour is more useful, so this patch series
reworks the FDT code to follow that and updates the very recently merged
arm64 idreg early command-line parsing as well.

I can just as easily argue that the kernel having the last say makes
sense.

Dunno, I'd say that's what CMDLINE_FORCE is for. Plus you'd be arguing
against both the documentation and the EFI stub implementation.

Regardless, I'm pretty sure there's someone out there relying on current
behavior. What is the impact of this change to other arches?

On arm64, I doubt it, as Android is the main user of this (where it's been
supported for 9 years with the documented behaviour).

The other option, then, is reverting CMDLINE_EXTEND from arm64 until this is
figured out. I think that's preferable to having divergent behaviour.

As for other architectures, I think the ATAGs-based solution on arch/arm/
gets it right:

  static int __init parse_tag_cmdline(const struct tag *tag)
  {
  #if defined(CONFIG_CMDLINE_EXTEND)
          strlcat(default_command_line, " ", COMMAND_LINE_SIZE);
          strlcat(default_command_line, tag->u.cmdline.cmdline,
                  COMMAND_LINE_SIZE);

For now I think we have two options for arm64: either fix the fdt code,
or revert CMDLINE_EXTEND until the PREPEND/APPEND series is merged. Which
do you prefer?

Will

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