On Sat, Apr 22, 2017 at 5:50 AM, Ville Syrjälä <ville.syrjala at linux.intel.com> wrote: > On Sat, Apr 22, 2017 at 01:07:57AM -0400, Ilia Mirkin wrote: >> On Fri, Apr 21, 2017 at 12:59 PM, Ville Syrjälä >> <ville.syrjala at linux.intel.com> wrote: >> > On Fri, Apr 21, 2017 at 10:49:49AM -0400, Ilia Mirkin wrote: >> >> On Fri, Apr 21, 2017 at 3:58 AM, Gerd Hoffmann <kraxel at redhat.com> 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. >> >> > >> >> > So, go update the comments for all 16+24+32 bpp RGB formats. >> >> > >> >> > Leaving the yuv formats as-is. I have no idea if and how those are used >> >> > on bigendian machines. >> >> >> >> I think this is premature. The current situation is that I can't get >> >> modetest to work *at all* on my NV34 / BE setup (I mean, it runs, just >> >> the colors displayed are wrong). I believe that currently it packs >> >> things in "cpu native endian". I've tried futzing with that without >> >> much success, although I didn't spend too much time on it. I have a >> >> NV34 plugged into my LE setup as well although I haven't tested to >> >> double-check that it all works there. However I'm quite sure it used >> >> to, as I used modetest to help develop the YUV overlay support for >> >> those GPUs. >> > >> > I just took a quick stab at fixing modetest to respect the current >> > wording in drm_fourcc.h: >> > >> > git://github.com/vsyrjala/libdrm.git modetest_endian >> >> Looks like there was some careless testing on my part :( So ... it >> looks like the current modetest without those changes does, in fact, >> work on NV34/BE. With the changes, it breaks (and the handling of the >> b* modes is a little broken in those patches -- they're not selectable >> from the cmdline.) Which means that, as Michel & co predicted, it >> appears to be taking BE input not LE input. This is very surprising to >> me, but it is what it is. As I mentioned before, the details of how >> the "BE" mode works on the GPUs is largely unknown to us beyond a few >> basics. Note that only XR24 works, AR24 ends up with all black >> displayed. This also happens on LE. > > Did you try 8bpp or 16bpp formats? I expect that if you've just blindly > enabled some magic byte swapper in the hardware it will only for > a specific pixel size. Thankfully dispnv04 exposes no such madness - just XR24 (and AR24, although that doesn't appear functional). Yes, it's likely that there's a byteswap happening somewhere. In fact the copy engines have parameters somewhere to tell how the swap should be done (basically what the element size is). I don't quite know how to set that though on this generation. I should poke at VRAM via the mmio peephole and see what's actually being stored. Although of course MMIO accesses are also auto-byteswapped. It's all just one big massive headache. -ilia
