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
dc22ee6fc18ce0f15424e753e8473c306ece95c1.
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>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 91b5f87..d809b03 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -4670,6 +4670,7 @@
/**
* intel_choose_pipe_bpp_dither - figure out what color depth the pipe should send
* @crtc: CRTC structure
+ * @mode: requested mode
*
* A pipe may be connected to one or more outputs. Based on the depth of the
* attached framebuffer, choose a good color depth to use on the pipe.
@@ -4681,13 +4682,15 @@
* HDMI supports only 8bpc or 12bpc, so clamp to 8bpc with dither for 10bpc
* Displays may support a restricted set as well, check EDID and clamp as
* appropriate.
+ * DP may want to dither down to 6bpc to fit larger modes
*
* RETURNS:
* Dithering requirement (i.e. false if display bpc and pipe bpc match,
* true if they don't match).
*/
static bool intel_choose_pipe_bpp_dither(struct drm_crtc *crtc,
- unsigned int *pipe_bpp)
+ unsigned int *pipe_bpp,
+ struct drm_display_mode *mode)
{
struct drm_device *dev = crtc->dev;
struct drm_i915_private *dev_priv = dev->dev_private;
@@ -4758,6 +4761,11 @@
}
}
+ if (mode->private_flags & INTEL_MODE_DP_FORCE_6BPC) {
+ DRM_DEBUG_KMS("Dithering DP to 6bpc\n");
+ display_bpc = 6;
+ }
+
/*
* We could just drive the pipe at the highest bpc all the time and
* enable dithering as needed, but that costs bandwidth. So choose
@@ -5019,6 +5027,16 @@
pipeconf &= ~PIPECONF_DOUBLE_WIDE;
}
+ /* default to 8bpc */
+ pipeconf &= ~(PIPECONF_BPP_MASK | PIPECONF_DITHER_EN);
+ if (is_dp) {
+ if (mode->private_flags & INTEL_MODE_DP_FORCE_6BPC) {
+ pipeconf |= PIPECONF_BPP_6 |
+ PIPECONF_DITHER_EN |
+ PIPECONF_DITHER_TYPE_SP;
+ }
+ }
+
dpll |= DPLL_VCO_ENABLE;
DRM_DEBUG_KMS("Mode for pipe %c:\n", pipe == 0 ? 'A' : 'B');
@@ -5480,7 +5498,7 @@
/* determine panel color depth */
temp = I915_READ(PIPECONF(pipe));
temp &= ~PIPE_BPC_MASK;
- dither = intel_choose_pipe_bpp_dither(crtc, &pipe_bpp);
+ dither = intel_choose_pipe_bpp_dither(crtc, &pipe_bpp, mode);
switch (pipe_bpp) {
case 18:
temp |= PIPE_6BPC;