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

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Date:   Fri, 21 Apr 2017 11:50:18 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     dri-devel@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...el.com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Ilia Mirkin <imirkin@...m.mit.edu>,
        Michel Dänzer <michel@...nzer.net>,
        Alex Deucher <alexdeucher@...il.com>,
        amd-gfx@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm: fourcc byteorder: brings header file comments in
 line with reality.

On Fr, 2017-04-21 at 12:25 +0300, Ville Syrjälä wrote:
> On Fri, Apr 21, 2017 at 09:58:24AM +0200, Gerd Hoffmann wrote:
> > While working on graphics support for virtual machines on ppc64 (which
> > exists in both little and big endian variants) I've figured the comments
> > for various drm fourcc formats in the header file don't match reality.
> > 
> > Comments says the RGB formats are little endian, but in practice they
> > are native endian.  Look at the drm_mode_legacy_fb_format() helper.  It
> > maps -- for example -- bpp/depth 32/24 to DRM_FORMAT_XRGB8888, no matter
> > whenever the machine is little endian or big endian.  The users of this
> > function (fbdev emulation, DRM_IOCTL_MODE_ADDFB) expect the framebuffer
> > is native endian, not little endian.  Most userspace also operates on
> > native endian only.
> 
> I'm not a fan of "native". Native to what? "CPU" or "host" is what I'd
> call it.

native == whatever the cpu is using.

I personally find "native" more intuitive, but at the end of the day I
don't mind much.  If people prefer "host" over "native" I'll change it.

> And what about the mxied endian case? Are you just going to pretend it
> doesn't exist or what?

What exactly do you mean with "mixed endian"?  The powerpc case, where
kernel + userspace can run in either big or little endian mode?  Or
something else?

cheers,
  Gerd