Re: [git pull] drm for 5.8-rc1

From: Karol Herbst <kherbst@redhat.com>
To: James Jones <jajones@nvidia.com>
Cc: dri-devel <dri-devel@lists.freedesktop.org>,
	Thierry Reding <treding@nvidia.com>,
	Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Subject: Re: [git pull] drm for 5.8-rc1
Date: Wed, 12 Aug 2020 20:51:20 +0200	[thread overview]
Message-ID: <CACO55tto89kT-_QKGjQ50Ht8U-4Dop6sTjNsbr1qHXhgNuDHEA@mail.gmail.com> (raw)
In-Reply-To: <2c5cf2e8-afd2-446d-1f27-2c225c65d447@nvidia.com>

in case you all were wondering, it works on xorg-server git because of
this commit: https://gitlab.freedesktop.org/xorg/xserver/-/commit/9b8999411033c9473cd68e92e4690a91aecf5b95

On Wed, Aug 12, 2020 at 8:25 PM James Jones <jajones@nvidia.com> wrote:
>
> On 8/12/20 10:40 AM, Alyssa Rosenzweig wrote:
> >> ...and in merging my code with Alyssa's new panfrost format modifier
> >> support, I see panfrost does the opposite of this and treats a format
> >> modifier list of only INVALID as "don't care".  I modeled the new nouveau
> >> behavior on the Iris driver.  Now I'm not sure which is correct :-(
> >
> > ....and neither am I. Uh-oh.
> >
> > I modeled the panfrost code after v3d_resource_create_with_modifiers,
> > which treats INVALID as "don't care". I can confirm the panfrost code
> > works (in the sense that it's functional on the machines I've tested),
> > but I don't know if it is actually correct. I think it is, since
> > otherwise you end up using linear in places it's unnecessary, but I'm
> > not sure where this is spec'd.
>
> It would depend on whether an app actually calls the function this way,
> and whether that app was tested I suppose.  If I'm interpreting the Iris
> code correctly and it doesn't break anything, then I'm assuming both
> implementations are equally valid in that nothing exercises this path,
> but it would be good to have the intended behavior documented somewhere
> so we can try to work towards consistent in case someone tries it in the
> future.
>
> My nouveau change runs afoul of assumptions in the tegra driver, but
> that's easy enough to fix in lockstep if desired.
>
> Also, heads up: I'll ping you on my format modifier cleanup MR once I've
> pushed the latest version.  The panfrost modifier usage was harder to
> merge into the refactoring than most, so it'll be good to have your
> review and if you have time, some testing.  I think I landed on an
> elegant solution, but open to suggestions.
>
> Thanks,
> -James
>

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