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SubjectRe: [PATCH] drm: fourcc byteorder: brings header file comments in line with reality.
On Fri, Apr 21, 2017 at 11:50:18AM +0200, Gerd Hoffmann wrote:
> 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.

"native" to me feels more like "native to the GPU" since these things
really are tied to the GPU not the CPU. That's also why I went with the
explicit endianness originally so that the driver could properly declare
what the GPU supports.

--
Ville Syrjälä
Intel OTC

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