linux-kernel - Re: [RFC PATCH 0/3] watchdog servicing during decompression

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Date:   Thu, 17 Oct 2019 14:34:52 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Gao Xiang <xiang@...nel.org>, kernel@...gutronix.de,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 0/3] watchdog servicing during decompression

On 17/10/2019 14.03, Russell King - ARM Linux admin wrote:
> We used to have this on ARM - it was called from the decompressor
> code via an arch_decomp_wdog() hook.
> 
> That code got removed because it is entirely unsuitable for a multi-
> platform kernel.  This looks like it takes an address for the watchdog
> from the Kconfig, and builds that into the decompressor, making the
> decompressor specific to that board or platform.
> 
> I'm not sure distros are going to like that given where we are with
> multiplatform kernels.

This is definitely not for multiplatform kernels or general distros,
it's for kernels that are built as part of a BSP for a specific board -
hence the "Say N unless you know you need this.".

I didn't know it used to exist. But I do know that something like this
is carried out-of-tree for lots of boards, so I thought I'd try to get
upstream support.

The first two patches, or something like them, would be nice on their
own, as that would minimize the conflicts when forward-porting the
board-specific patch. But such a half-implemented feature that requires
out-of-tree patches to actually do anything useful of course won't fly.

I'm not really a big fan of the third patch, even though it does work
for all the cases I've encountered so far - I'm sure there would be
boards where a much more complicated solution would be needed. Another
method I thought of was to just supply a __weak no-op
decompress_keepalive(), and then have a config option to point at an
extra object file to link into the compressed/vmlinux (similar to the
initramfs_source option that also points to some external resource).

But if the mainline kernel doesn't want anything like this
re-introduced, that's also fine, that just means a bit of job security.

Rasmus