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>
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@ -1922,7 +1922,10 @@
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/* Display & cursor control */
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/* dithering flag on Ironlake */
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#define PIPE_ENABLE_DITHER (1 << 4)
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#define PIPE_ENABLE_DITHER (1 << 4)
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#define PIPE_DITHER_TYPE_MASK (3 << 2)
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#define PIPE_DITHER_TYPE_SPATIAL (0 << 2)
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#define PIPE_DITHER_TYPE_ST01 (1 << 2)
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/* Pipe A */
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#define PIPEADSL 0x70000
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#define PIPEACONF 0x70008
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@ -3677,14 +3677,16 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
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/* set the dithering flag */
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if (IS_I965G(dev)) {
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if (dev_priv->lvds_dither) {
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if (HAS_PCH_SPLIT(dev))
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if (HAS_PCH_SPLIT(dev)) {
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pipeconf |= PIPE_ENABLE_DITHER;
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else
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pipeconf |= PIPE_DITHER_TYPE_ST01;
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} else
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lvds |= LVDS_ENABLE_DITHER;
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} else {
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if (HAS_PCH_SPLIT(dev))
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if (HAS_PCH_SPLIT(dev)) {
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pipeconf &= ~PIPE_ENABLE_DITHER;
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else
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pipeconf &= ~PIPE_DITHER_TYPE_MASK;
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} else
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lvds &= ~LVDS_ENABLE_DITHER;
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}
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}
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