[Intel-gfx] [PATCH] drm/i915: implement high-bpc + pipeconf-dither support for g4x/vlv

[Daniel Vetter]

The current code is rather ... ugly. The only thing it managed to pull
off is getting 6bpc on DP working on g4x. Then someone added another
custom hack for 6bpc eDP on vlv. Fix up this entire mess by properly
implementing the PIPECONF-based dither/bpc controls on g4x/vlv.

Note that compared to pch based platforms g4x/vlv don't support 12bpc
modes. g4x is already caught, extend the check for vlv.

The other fixup is to restrict the lvds-specific dithering to early
gen4 devices - g4x should use the pipeconf dither controls. Note that
on gen2/3 the dither control is in the panel fitter even.

v2: Don't enable dithering when the pipe is in 10 bpc mode. Quoting
from Bspec "PIPEACONF - Pipe A Configuration Register, bit 4":

"Programming note: Dithering should only be enabled for 8 bpc or 6
bpc."

v3: Actually drop the old ugly dither code.

v4: Explain in a short comment why g4x/vlv shouldn't dither for 30 bpp
pipes (Jesse).

Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/intel_display.c | 35 +++++++++++++++++++++--------------
 drivers/gpu/drm/i915/intel_lvds.c    |  2 +-
 2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 8c36376..7f1ab8b 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -4605,22 +4605,29 @@ static void i9xx_set_pipeconf(struct intel_crtc *intel_crtc)
 			pipeconf &= ~PIPECONF_DOUBLE_WIDE;
 	}
 
-	/* default to 8bpc */
-	pipeconf &= ~(PIPECONF_BPC_MASK | PIPECONF_DITHER_EN);
-	if (intel_crtc->config.has_dp_encoder) {
-		if (intel_crtc->config.dither) {
-			pipeconf |= PIPECONF_6BPC |
-				    PIPECONF_DITHER_EN |
+	/* only g4x and later have fancy bpc/dither controls */
+	if (IS_G4X(dev) || IS_VALLEYVIEW(dev)) {
+		pipeconf &= ~(PIPECONF_BPC_MASK | PIPECONF_DITHER_EN);
+
+		/* Bspec claims that we can't use dithering for 30bpp pipes. */
+		if (intel_crtc->config.dither && intel_crtc->config.pipe_bpp != 30)
+			pipeconf |= PIPECONF_DITHER_EN |
 				    PIPECONF_DITHER_TYPE_SP;
-		}
-	}
 
-	if (IS_VALLEYVIEW(dev) && intel_pipe_has_type(&intel_crtc->base,
-						      INTEL_OUTPUT_EDP)) {
-		if (intel_crtc->config.dither) {
-			pipeconf |= PIPECONF_6BPC |
-					PIPECONF_ENABLE |
-					I965_PIPECONF_ACTIVE;
+		pipeconf &= ~PIPECONF_BPC_MASK;
+		switch (intel_crtc->config.pipe_bpp) {
+		case 18:
+			pipeconf |= PIPECONF_6BPC;
+			break;
+		case 24:
+			pipeconf |= PIPECONF_8BPC;
+			break;
+		case 30:
+			pipeconf |= PIPECONF_10BPC;
+			break;
+		default:
+			/* Case prevented by intel_choose_pipe_bpp_dither. */
+			BUG();
 		}
 	}
 
diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
index 58a98ff..094f3c5 100644
--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -135,7 +135,7 @@ static void intel_pre_pll_enable_lvds(struct intel_encoder *encoder)
 	/* Set the dithering flag on LVDS as needed, note that there is no
 	 * special lvds dither control bit on pch-split platforms, dithering is
 	 * only controlled through the PIPECONF reg. */
-	if (INTEL_INFO(dev)->gen == 4) {
+	if (INTEL_INFO(dev)->gen == 4 && !IS_G4X(dev)) {
 		if (intel_crtc->config.dither)
 			temp |= LVDS_ENABLE_DITHER;
 		else
-- 
1.7.11.7