Commit 0a31a448 authored Apr 19, 2010 by Adam Jackson Committed by Eric Anholt May 07, 2010

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>

parent 9e51159c

drivers/gpu/drm/i915/i915_reg.h

+4 −1

Original line number	Diff line number	Diff line
		@@ -1923,6 +1923,9 @@

		/* dithering flag on Ironlake */
		#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

drivers/gpu/drm/i915/intel_display.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -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;
		}
		}