linux-kernel - Re: [RFC] drm/fourcc: Add a modifier for contiguous memory

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Date:   Tue, 29 Nov 2022 18:46:03 +0800
From:   Hsia-Jun Li <Randy.Li@...aptics.com>
To:     Simon Ser <contact@...rsion.fr>
Cc:     dri-devel@...ts.freedesktop.org, ayaka@...lik.info,
        linux-kernel@...r.kernel.org, nicolas@...fresne.ca,
        hverkuil@...all.nl, tzimmermann@...e.de, tfiga@...omium.org,
        linux-media@...r.kernel.org
Subject: Re: [RFC] drm/fourcc: Add a modifier for contiguous memory



On 11/29/22 18:18, Simon Ser wrote:
> CAUTION: Email originated externally, do not click links or open attachments unless you recognize the sender and know the content is safe.
> 
> 
> Format modifiers are for the buffer layout only, not for the allocation
> parameters, placement, etc. See the doc comment at the top of
> drm_fourcc.h.
In the v4l2 mail list, we have such proposal that dropping the pixel 
formats(not the codec formats) from v4l2 header completely, as the 
growing of tile pixel formats.
But we can't get rid of those variants about non-contiguous(the same 
value FOURCC in v4l2 are all for the contiguous memory).

Before I solve this problem, I believe the support for tile formats in 
v4l2 would never be stable.

The most common way here is to hack the pixel format modifier, then 
userspace library could be aware this in allocation and get properties 
of the drm_planes.

Or another way, we could add a common plane property, indicated that 
whether the driver requests contiguous memory plane for a format?
-- 
Hsia-Jun(Randy) Li