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Message-ID: <1492768218.25675.33.camel@redhat.com>
Subject: Re: [PATCH] drm: fourcc byteorder: brings header file comments in
 line with reality.
From: Gerd Hoffmann <kraxel@redhat.com>
To: Ville =?ISO-8859-1?Q?Syrj=E4l=E4?= <ville.syrjala@linux.intel.com>
Cc: dri-devel@lists.freedesktop.org,
        Daniel Vetter <daniel.vetter@intel.com>,
        Pekka Paalanen <ppaalanen@gmail.com>,
        Ilia Mirkin <imirkin@alum.mit.edu>,
        Michel =?ISO-8859-1?Q?D=E4nzer?= <michel@daenzer.net>,
        Alex Deucher <alexdeucher@gmail.com>, amd-gfx@lists.freedesktop.org,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Sean Paul <seanpaul@chromium.org>, David Airlie <airlied@linux.ie>,
        open list <linux-kernel@vger.kernel.org>
Date: Fri, 21 Apr 2017 11:50:18 +0200
In-Reply-To: <20170421092530.GE30290@intel.com>
References: <20170421075825.6307-1-kraxel@redhat.com>
         <20170421092530.GE30290@intel.com>
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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