R200 DRM/KMS

[Steven Newbury]

On Mon, 2015-07-06 at 12:25 -0400, Alex Deucher wrote:
> On Mon, Jul 6, 2015 at 9:39 AM, Steven Newbury <steve at snewbury.org.uk
> > wrote:
> > Hi,
> > I've been trying to get DRM/KMS working with the current graphics
> > stack (xf86-video-ati 7.5, xserver-1.17) on a R200 series card.  I
> > assumed this should be working since KMS was implemented for it a
> > while back, and it has been working with xf86-video-ati-6.x.
> > 
> > Unfortunately, it doesn't seem to work.
> > 
> > I've narrowed it down to drmSetInterfaceVersion() failing when 
> > called
> > from the ATI driver (in radeon_kms.c).  This is a bit strange 
> > since,
> > /sys/class/drm/version correctly reports 1.1.0 20060810.  Presuably
> > it's getting the correct fd for the DRM master otherwise it should
> > bail earlier?
> > 
> > 
> > Googling confirms others have had the same issue, and generally the
> > resolution has been to stick with the old driver.
> > 
> > Should this be working?  Is it known to be broken?
> 
> It should be working.  Make sure the kernel driver has kms enabled,
> firmware available, and that the kernel driver is loaded before
> starting X.  If the kernel driver is not loaded before X starts you
> can get a version mis-match error.

Yes, using Gentoos 4.1.1 kernel, driver is definitely loaded, with
modeset=1, which is working, all sysfs entries are there.  gdm manages
to fall back to starting up an X session without using DRM swrast
-only, not something you want to experience on such a weak CPU!

Manually starting X fails with the "[drm] failed to set drm interface
version." error.

It's a very old system, PCI-only(!) Coppermine-128, belonging to a
friend.  The system previously was (very slowly) running Ubuntu 10
LTS, I think.  It's not my machine so I'm not able to have continuous
access, but R200 DRM/KMS was working.  Apparently, Ubuntu no longer
support R200, so no further updates were possible. 

My friend can't afford a new machine at the moment; and since I'm a
long time Gentoo dev I took it upon myself to build him a optimized
desktop with gcc-5, where possible LTO, -Os, -march=pentium3 with the
system L1 and L2 cache size information.  It's quite possible some
part of the gfx stack is miscompiled, I tested it pretty throughly
under qemu (with qxl) before deployment, but that of course didn't
exercise the R200 driver.  FWIW, other than the failing DRI,
performance is surprisingly OK, not super fast obviously, but a *lot*
better than under Ubuntu! (start-up time is alot quicker, by an order
of magnitude!)

I'm attempting to downgrade the xserver and drivers (on the live
system) to see if that works, you can imagine that takes a little
while on a Coppermine-128!  I'll find out tomorrow.  Otherwise, I
guess I'm recompiling the stack with gcc-4.9 and no-LTO...
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