linux-kernel - Re: [PATCH 2/3] drm/panfrost: Use u64 for size in lock

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Message-ID: <77CFD756-7F02-4CBA-9E58-3EDA2167620E@arm.com>
Date:   Mon, 23 Aug 2021 22:57:56 +0100
From:   Steven Price <steven.price@....com>
To:     dri-devel@...ts.freedesktop.org,
        Alyssa Rosenzweig <alyssa@...labora.com>
CC:     Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Rob Herring <robh@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org,
        Chris Morgan <macromorgan@...mail.com>
Subject: Re: [PATCH 2/3] drm/panfrost: Use u64 for size in lock_region

On 23 August 2021 22:11:09 BST, Alyssa Rosenzweig <alyssa@...labora.com> wrote:
>> > Mali virtual addresses are 48-bit. Use a u64 instead of size_t to ensure
>> > we can express the "lock everything" condition as ~0ULL without relying
>> > on platform-specific behaviour.
>> 
>> 'platform-specific behaviour' makes it sound like this is something to
>> do with a particular board. This is 32bit/64bit - it's going to be
>> broken on 32bit: large lock regions are not going to work.
>
>Oh, my. I used the term as a weasel word since the spec is loose on how
>big a size_t actually is. But if this is causing actual breakage on
>armv7 we're in trouble. I'll add a Cc stable tag on v2, unless the Fixes
>implies that?

The usual practice is to put CC: stable in the commit message or the fixes tag (no need to actually CC the stable email address). So just Fixes: should work

>Thanks for pointing this out.

It's not actually quite so bad as it could be as >4GB regions are unlikely (especially on 32bit), but the GPU does of course support such a thing.

Thanks,
Steve