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

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Date:   Mon, 24 Apr 2017 15:33:07 +0900
From:   Michel Dänzer <michel@...nzer.net>
To:     Ilia Mirkin <imirkin@...m.mit.edu>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     amd-gfx@...ts.freedesktop.org,
        open list <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH] drm: fourcc byteorder: brings header file comments in
 line with reality.

On 23/04/17 04:24 AM, Ilia Mirkin wrote:
> 
> fbdev also creates fb's that expect cpu endianness, as disabling the
> byteswap logic caused a green fbcon terminal to show up. (So at least
> something somewhere in the fbcon -> nouveau's fbdev emulation pipeline
> is expecting cpu endianness. This happens both with nouveau's fbdev
> accel logic and without.)

In theory, there's FB_FOREIGN_ENDIAN for that. But in practice it's
probably useless because little if any userspace even checks for it, let
alone handles it correctly.


> So I think the current situation, at least wrt pre-nv50 nouveau, is
> that XRGB/ARGB8888 are "special", since they are the only things
> exposed by drm_crtc_init. I believe those definitions should be
> updated to note that they're cpu-endian-specific (or another way of
> phrasing it more diplomatically is that they're array formats rather
> than packed formats).

That would be incorrect. :) The memory layout of 8-bit-per-component
array formats doesn't depend on endianness, that of packed formats does.
(DRM_FORMAT_*8 as currently defined are thus effectively array formats)


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer