linux-kernel - Re: [PATCH] drm/vc4: Add support for SAND modifier.

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Date:   Fri, 16 Mar 2018 15:05:59 -0700
From:   Eric Anholt <eric@...olt.net>
To:     Daniel Stone <daniel@...ishbar.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Dave Stevenson <dave.stevenson@...pberrypi.org>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Daniel Stone <daniels@...labora.com>
Subject: Re: [PATCH] drm/vc4: Add support for SAND modifier.

Daniel Stone <daniel@...ishbar.org> writes:

> Hey Eric,
>
> On 3 March 2018 at 01:34, Eric Anholt <eric@...olt.net> wrote:
>> Ccing a couple of folks who are likely to have opinions about
>> drm_fourcc.h additions (Do we have enough docs?  Are the macros OK?),
>> and Bootlin who are likely reviewers.
>>
>> The plan is to use these modifiers in VC4 GL imports as well, and for
>> buffers coming from the v4l2 mmal camera driver.  You can find a demo
>> using this in KMS planes at
>> https://github.com/anholt/drm_mmal/commit/sand for now.
>
> I had a dig through and this seems like the most sensible thing to do
> if you have a reasonable variety of tile heights. If you only see a
> couple of combinations in the wild, then hardcoding them as separate
> modifiers might make things easier than hiving off 24 bits. If you do
> keep the split though, and especially if you're envisioning future
> flexible tile formats, maybe something like an 8 code / 48 params
> split would make more sense.
>
> Either way, those are just my opinions (you did ask), and I don't see
> anything really objectionable, so if you think that's a good split
> then this is:
> Acked-by: Daniel Stone <daniels@...labora.com>

I had been thinking of potentially specifying a meaning for the other 24
bits (separate U/V plane v stride if set, if we ever get a component
that needs to do that), so I went ahead and did this, along with a
couple of fixes due to Ville's patch.

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