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

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Message-ID: <CAMuHMdWxbF6OsP0+c5hqxDTfHu+Wetcitk1yFiOPECoLtD6zyg@mail.gmail.com>
Date:   Tue, 12 Jul 2022 11:10:41 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Michel Dänzer <michel.daenzer@...lbox.org>
Cc:     Gerd Hoffmann <kraxel@...hat.com>,
        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

Hi Michel,

On Tue, Jul 12, 2022 at 11:09 AM Michel Dänzer
<michel.daenzer@...lbox.org> wrote:
> 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).

Sure, I'll update the patch accordingly.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds