linux-kernel - Re: [PATCH v2 3/5] drm/v3d: Add support for compute shader dispatch.

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Date:   Wed, 17 Apr 2019 14:53:33 -0700
From:   Eric Anholt <eric@...olt.net>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        david.emett@...adcom.com, thomas.spurden@...adcom.com
Subject: Re: [PATCH v2 3/5] drm/v3d: Add support for compute shader dispatch.

Eric Anholt <eric@...olt.net> writes:

> The compute shader dispatch interface is pretty simple -- just pass in
> the regs that userspace has passed us, with no CLs to run.  However,
> with no CL to run it means that we need to do manual cache flushing of
> the L2 after the HW execution completes (for SSBO, atomic, and
> image_load_store writes that are the output of compute shaders).
>
> This doesn't yet expose the L2 cache's ability to have a region of the
> address space not write back to memory (which could be used for
> shared_var storage).
>
> So far, the Mesa side has been tested on V3D v4.2 simpenrose (passing
> the ES31 tests), and on the kernel side on 7278 (failing atomic
> compswap tests in a way that doesn't reproduce on simpenrose).

Fixed the compswap issue in Mesa.  Looks like cmpxchg needed the TYPE
field set to vec2 instead of 32-bit, since there are two values written
to TMUD.  The spec says the field is ignored, but that doesn't seem to
be the case.

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