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

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Message-ID: <20220712090305.44jq3olwhwypisoc@sirius.home.kraxel.org>
Date:   Tue, 12 Jul 2022 11:03:05 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Michel Dänzer <michel.daenzer@...lbox.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Noralf Trønnes <noralf@...nnes.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Linux/m68k <linux-m68k@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] drm/fourcc: Add missing big-endian XRGB1555 and
 RGB565 formats

> > 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 ;)

thanks,
  Gerd