On 10/07/2012 02:40 PM, Daniel Vetter wrote:
On Fri, Oct 05, 2012 at 05:08:04PM -0700, Kenneth Graunke wrote:
According to internal bug reports, guardband clipping sometimes
incorrectly discards triangles unless bit 5 of 3D_CHICKEN3 ("SF Disable
fastclip optimization when culled") is set.
Experimentally, this appears to be true. With guardband clipping
enabled, Dante randomly loses triangles unless bit 5 is set.
The BSpec indicates that the default value of the register is supposed
to be 0x20 (just bit 5), but on my Lenovo X220 it appears to be 0.
Daniel attempted to implement the workaround via a kernel patch named
drm/i915: implement w/a for incorrect guarband clipping
but unfortunately, the write isn't taking effect for some reason.
Fixes clipping issues in Dante.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=53946
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=55523
Cc: Oliver McFadden <oliver.mcfad...@linux.intel.com>
Cc: nkalk...@web.de
Cc: Eric Anholt <e...@anholt.net>
Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
Does this really work as advertised?
The reg_read_ioctl is brand-new, only merged into 3.7. And it has a
whitelist of registers that userspace is allowed to read, and CHICKEN_3 is
not on it.
-Daniel
Oh. Damn. I neglected to check that it ever returned success.
The fact that it's new is fine, as the fix is newer. If the ioctl
didn't exist, it would simply turn off guardband clipping.
But you're right, since we can't read 3D_CHICKEN3, we'd just turn it off
unilaterally. That sucks.
I'm not sure what to do then.
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