linux-kernel - Re: [PATCH RESEND] drm/vc4: Make sure to emit a tile coordinates between two MSAA loads.

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Message-ID: <87imwa38gr.fsf@anholt.net>
Date:   Fri, 22 Mar 2019 14:28:04 -0700
From:   Eric Anholt <eric@...olt.net>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org,
        Maxime Ripard <maxime.ripard@...tlin.com>
Subject: Re: [PATCH RESEND] drm/vc4: Make sure to emit a tile coordinates between two MSAA loads.

Paul Kocialkowski <paul.kocialkowski@...tlin.com> writes:

> Hi,
>
> Le mercredi 06 février 2019 à 15:25 -0800, Eric Anholt a écrit :
>> The HW only executes a load once the tile coordinates packet happens,
>> and only tracks one at a time, so by emitting our two MSAA loads back
>> to back we would end up with an undefined color or Z buffer.
>
> This change deals with things that I'm not very familiar with, but here
> is my take on what is happening here:
>
> - When we have to do more than a single load in the same render command
> list, we need to send out tile coordinates and a dummy store in between
> the two, because of internal architecture requirements of the GPU;
> - We're dealing with the color buffer first and then the z-stencil
> buffer;
> - As a result, we need to issue that dummy store in the block handling
> the z-stencil, if there was a previous color load in the rcl;
> - We previously only did that for non-MSAA z-stencil buffers (without
> the FULL_RES flag);
> - The same thing actually needs to be done for the MSAA case too, as
> the reason why we need that dummy store also applies to MSAA loads.
>
> If my understanding is correct, then consider this:
> Reviewed-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>

This is all correct.  Thanks!

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