linux-kernel - Re: [PATCH 3/3] drm/panfrost: Clamp lock region to Bifrost minimum

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Message-ID: <FA069E32-03E1-4193-8918-C750A4ECE5F8@arm.com>
Date:   Mon, 23 Aug 2021 23:02:05 +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>, stable@...r.kernel.org
Subject: Re: [PATCH 3/3] drm/panfrost: Clamp lock region to Bifrost minimum

On 23 August 2021 22:13:45 BST, Alyssa Rosenzweig <alyssa@...labora.com> wrote:
>> > When locking a region, we currently clamp to a PAGE_SIZE as the minimum
>> > lock region. While this is valid for Midgard, it is invalid for Bifrost,
>> 
>> While the spec does seem to state it's invalid for Bifrost - kbase
>> didn't bother with a lower clamp for a long time. I actually think this
>> is in many ways more of a spec bug: i.e. implementation details of the
>> round-up that the hardware does. But it's much safer following the spec
>> ;) And it seems like kbase eventually caught up too.
>
>Yeah, makes sense. Should I drop the Cc: stable in that case? If the
>issue is purely theoretical.

I think it might still be worth fixing. Early Bifrost should be fine, but something triggered a bug report that caused kbase to be fixed, so I'm less confident that there's nothing out there that cares. Following both kbase and the spec seems the safest approach.

Thanks,
Steve