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

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Date:   Tue, 18 Apr 2017 23:28:06 -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 11:19 PM, Ilia Mirkin <imirkin@...m.mit.edu> wrote:
> 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.

(And as Michel points out, the patch doesn't actually touch anything,
just comments. I originally thought it changed format -> fourcc
mapping.)