linux-kernel - Re: [RFC PATCH 18/20] lib: image-formats: Add v4l2 formats support

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Date:   Wed, 20 Mar 2019 18:15:54 +0000
From:   Brian Starkey <Brian.Starkey@....com>
To:     Nicolas Dufresne <nicolas@...fresne.ca>
CC:     Maxime Ripard <maxime.ripard@...tlin.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        nd <nd@....com>
Subject: Re: [RFC PATCH 18/20] lib: image-formats: Add v4l2 formats support

On Tue, Mar 19, 2019 at 07:29:18PM -0400, Nicolas Dufresne wrote:
> All RGB mapping should be surrounded by ifdef, because many (not all)
> DRM formats represent the order of component when placed in a CPU
> register, unlike V4L2 which uses memory order. I've pick this one
> randomly, but this one on most system, little endian, will match
> V4L2_PIX_FMT_XBGR32. This type of complex mapping can be found in
> multiple places, notably in GStreamer:
> 
> https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/blob/master/sys/kms/gstkmsutils.c#L45
> 

I do sort-of wonder if it's worth trying to switch to common fourccs
between DRM and V4L2 (and whatever else there is).

The V4L2 formats list is quite incomplete and a little quirky in
places (V4L2_PIX_FORMAT_XBGR32 and V4L2_PIX_FORMAT_XRGB32 naming
inconsistency being one. 'X' isn't even next to 'B' in XBGR32).

At least for newly-added formats, not using a common definition
doesn't make a lot of sense to me. Longer term, I also don't really
see any downsides to unification.

-Brian