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drm/i915: Use spatio-temporal dithering on PCH

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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>
This commit is contained in:
Adam Jackson 2010-04-19 15:57:25 -04:00 committed by Eric Anholt
parent 9e51159c14
commit 0a31a44865
2 changed files with 10 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
drivers/gpu/drm/i915/i915_reg.h
View File

@ -1922,7 +1922,10 @@
/* Display & cursor control */
/* dithering flag on Ironlake */
#define PIPE_ENABLE_DITHER (1 << 4)
#define PIPE_ENABLE_DITHER (1 << 4)
#define PIPE_DITHER_TYPE_MASK (3 << 2)
#define PIPE_DITHER_TYPE_SPATIAL (0 << 2)
#define PIPE_DITHER_TYPE_ST01 (1 << 2)
/* Pipe A */
#define PIPEADSL 0x70000
#define PIPEACONF 0x70008

10
drivers/gpu/drm/i915/intel_display.c
View File

@ -3677,14 +3677,16 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
/* 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;
}
}