[Intel-gfx] [PATCH] drm/i915: set DP Main Stream Attribute for color range on DDI platforms

[Jani Nikula]

Since Haswell we have no color range indication either in the pipe or
port registers for DP. Instead, there's a separate register for setting
the DP Main Stream Attributes (MSA) directly. The MSA register
definition makes no references to colorimetry, just a vague reference to
the DP spec. The connection to the color range was lost.

Apparently we've failed to set the proper MSA bit for limited, or CEA,
range ever since the first DDI platforms. We've started setting other
MSA parameters since commit dae847991a43 ("drm/i915: add
intel_ddi_set_pipe_settings").

Without the crucial bit of information, the DP sink has no way of
knowing the source is actually transmitting limited range RGB, leading
to "washed out" colors. With the colorimetry information, compliant
sinks should be able to handle the limited range properly. Native
(i.e. non-LSPCON) HDMI was not affected because we do pass the color
range via AVI infoframes.

Though not the root cause, the problem was made worse for DDI platforms
with commit 55bc60db5988 ("drm/i915: Add "Automatic" mode for the
"Broadcast RGB" property"), which selects limited range RGB
automatically based on the mode, as per the DP, HDMI and CEA specs.

After all these years, the fix boils down to flipping one bit.

[Per testing reports, this fixes DP sinks, but not the LSPCON. My
 educated guess is that the LSPCON fails to turn the CEA range MSA into
 AVI infoframes for HDMI.]

Reported-by: Michał Kopeć <mkopec12 at gmail.com>
Reported-by: N. W. <nw9165-3201 at yahoo.com>
Reported-by: Nicholas Stommel <nicholas.stommel at gmail.com>
Reported-by: Tom Yan <tom.ty89 at gmail.com>
Tested-by: Nicholas Stommel <nicholas.stommel at gmail.com>
References: https://bugs.freedesktop.org/show_bug.cgi?id=100023
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107476
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=94921
Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: <stable at vger.kernel.org> # v3.9+
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h  | 1 +
 drivers/gpu/drm/i915/intel_ddi.c | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 17575cfc22b5..0c9f03dda569 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -9246,6 +9246,7 @@ enum skl_power_gate {
 #define  TRANS_MSA_10_BPC		(2 << 5)
 #define  TRANS_MSA_12_BPC		(3 << 5)
 #define  TRANS_MSA_16_BPC		(4 << 5)
+#define  TRANS_MSA_CEA_RANGE		(1 << 3)
 
 /* LCPLL Control */
 #define LCPLL_CTL			_MMIO(0x130040)
diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 0adc043529f2..6f7be066c8f2 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -1685,6 +1685,10 @@ void intel_ddi_set_pipe_settings(const struct intel_crtc_state *crtc_state)
 	WARN_ON(transcoder_is_dsi(cpu_transcoder));
 
 	temp = TRANS_MSA_SYNC_CLK;
+
+	if (crtc_state->limited_color_range)
+		temp |= TRANS_MSA_CEA_RANGE;
+
 	switch (crtc_state->pipe_bpp) {
 	case 18:
 		temp |= TRANS_MSA_6_BPC;
-- 
2.11.0