linux-kernel - Re: [RfC PATCH] drm: fourcc byteorder: brings header file comments in line with reality.

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Message-ID: <CAKb7UvhREjZ9tqarrzYZuta3b66xqRMtBorWxRZN5ECOPyvHbw@mail.gmail.com>
Date:   Tue, 18 Apr 2017 23:19:22 -0400
From:   Ilia Mirkin <imirkin@...m.mit.edu>
To:     Michel Dänzer <michel@...nzer.net>
Cc:     Gerd Hoffmann <kraxel@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        amd-gfx@...ts.freedesktop.org,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RfC PATCH] drm: fourcc byteorder: brings header file comments in
 line with reality.

On Tue, Apr 18, 2017 at 9:01 PM, Michel Dänzer <michel@...nzer.net> wrote:
> On 18/04/17 07:14 PM, Gerd Hoffmann wrote:
>>   Hi,
>>
>>>> Quite true that this proves nothing. However one should note that
>>>> fbcon -> fbdev works,
>>>
>>> BTW, this supports Gerd's patch, since the KMS fbdev emulation code uses
>>> e.g. DRM_FORMAT_XRGB8888 for depth/bpp 24/32, and the fbdev API uses
>>> native endian packed colour values.
>>
>> Same is true for DRM_IOCTL_MODE_ADDFB, with depth/bpp 24/32 you'll get
>> DRM_FORMAT_XRGB8888 (only DRM_IOCTL_MODE_ADDFB2 allows userspace specify
>> fourcc formats directly).
>
> Right, and since all major Xorg drivers use DRM_IOCTL_MODE_ADDFB,
> they're effectively using DRM_FORMAT_XRGB8888 as native endianness as well.

In the meanwhile, it has been pointed out to me that pre-nv50 display
code actually doesn't use DRM_FORMAT_* at all -- it uses some helpers
which end up advertising XR24 / AR24. However from what I can tell,
that's not a well-reasoned selection. Either way, I'm going to test
Gerd's patch, hopefully during the week, or weekend at the latest. My
current suspicion is that it will have no effect on nouveau either
way. We'll find out.

  -ilia