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

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Date:   Mon, 23 Aug 2021 17:11:09 -0400
From:   Alyssa Rosenzweig <alyssa@...labora.com>
To:     Steven Price <steven.price@....com>
Cc:     Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        dri-devel@...ts.freedesktop.org, 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

> > 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?

Thanks for pointing this out.