drm/i915: Use spatio-temporal dithering on PCH
Spatial dither is better than nothing, but ST is even better.
(from ajax's followup message:)
I noticed this with:
http://ajax.fedorapeople.org/YellowFlower.jpg
set as my desktop background in Gnome on a 1280x800 machine (in
particular, a Sony Vaio VPCB1 with 6-bit panel and a rather bright black
level). Easiest way to test this is by poking at PIPEACONF with
intel_reg_write directly:
% sudo intel_reg_write 0x70008 0xc0000040 # no dither
% sudo intel_reg_write 0x70008 0xc0000050 # spatial
% sudo intel_reg_write 0x70008 0xc0000054 # ST
I notice it especially strongly in the relatively flat dark area in the
top left. Closer than about 18" I can see a noticeable checkerboard
pattern with plain spatial dithering. ST smooths that out; I can still
tell that it's lacking color precision, but it's not offensive.
Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 3836f56..119a41a 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3677,14 +3677,16 @@
/* set the dithering flag */
if (IS_I965G(dev)) {
if (dev_priv->lvds_dither) {
- if (HAS_PCH_SPLIT(dev))
+ if (HAS_PCH_SPLIT(dev)) {
pipeconf |= PIPE_ENABLE_DITHER;
- else
+ pipeconf |= PIPE_DITHER_TYPE_ST01;
+ } else
lvds |= LVDS_ENABLE_DITHER;
} else {
- if (HAS_PCH_SPLIT(dev))
+ if (HAS_PCH_SPLIT(dev)) {
pipeconf &= ~PIPE_ENABLE_DITHER;
- else
+ pipeconf &= ~PIPE_DITHER_TYPE_MASK;
+ } else
lvds &= ~LVDS_ENABLE_DITHER;
}
}
