linux-kernel - Re: [PATCH 1/3] drm/fourcc: Add missing big-endian XRGB1555 and RGB565 formats

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Message-ID: <69a6aac7-0d48-7361-9750-8f242d374d60@mailbox.org>
Date:   Tue, 12 Jul 2022 11:09:25 +0200
From:   Michel Dänzer <michel.daenzer@...lbox.org>
To:     Gerd Hoffmann <kraxel@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Linux/m68k <linux-m68k@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Noralf Trønnes <noralf@...nnes.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 1/3] drm/fourcc: Add missing big-endian XRGB1555 and
 RGB565 formats

On 2022-07-12 11:03, Gerd Hoffmann wrote:
>>> As described above DRM_FORMAT_HOST_RGB565 means bigendian on bigendian
>>> hosts and little endian on little endian hosts.  Which is not correct
>>> when your hardware does big endian no matter what.
>>
>> But (a) drm_driver_legacy_fb_format() uses DRM_FORMAT_HOST_RGB565
>> if quirk_addfb_prefer_host_byte_order is set,
> 
> Ah, right.  Missed that in 'git grep' output.  Given that traditional
> fbdev behavior is to expect native byte order using
> DRM_FORMAT_HOST_RGB565 there makes sense indeed.
> 
> Scratch my comment about it being unused then ;)

DRM_FORMAT_RGB565 | DRM_FORMAT_BIG_ENDIAN is still what the driver should use conceptually, and should match DRM_FORMAT_HOST_RGB565 in drm_driver_legacy_fb_format on a big endian host (which is presumably always the case for the atari driver).


-- 
Earthling Michel Dänzer            |                  https://redhat.com
Libre software enthusiast          |         Mesa and Xwayland developer