drm/i915/dp: Dither down to 6bpc if it makes the mode fit

Some active adaptors (VGA usually) only have two lanes at 2.7GHz.
That's a maximum pixel clock of 144MHz at 8bpc, but 192MHz at 6bpc.

Fixes Asus UX31 panel being black at startup due to no valid modes since
dc22ee6fc1.

v2: Rebased to current code, resulting in the fix applying to EDP panels as
    well.  Also changed from spatio-temporal to just spatial dithering on
    pre-ironlake, to be conssitent (and less visual flicker)

Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Tested-by: Eric Anholt <eric@anholt.net>
Tested-by: Dirk Hohndel <hohndel@infradead.org>
Signed-off-by: Keith Packard <keithp@keithp.com>
This commit is contained in:
Adam Jackson
2011-12-13 15:41:00 -08:00
committed by Keith Packard
parent f45b55575c
commit 3b5c78a35c
3 changed files with 39 additions and 8 deletions

View File

@@ -110,6 +110,7 @@
/* drm_display_mode->private_flags */
#define INTEL_MODE_PIXEL_MULTIPLIER_SHIFT (0x0)
#define INTEL_MODE_PIXEL_MULTIPLIER_MASK (0xf << INTEL_MODE_PIXEL_MULTIPLIER_SHIFT)
#define INTEL_MODE_DP_FORCE_6BPC (0x10)
static inline void
intel_mode_set_pixel_multiplier(struct drm_display_mode *mode,