[PATCH 3/5][SRU][U/OEM-5.10] drm/i915: Check for unsupported DP link rates during initial commit

[Koba Ko]

From: Imre Deak <imre.deak at intel.com>

https://bugs.launchpad.net/bugs/1908885 

Some BIOSes set an unsupported/imprecise DP link rate (for instance on
TGL A stepping). Make sure that we do an encoder recompute and a modeset
in this case.

Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Imre Deak <imre.deak at intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201003001846.1271151-4-imre.deak@intel.com
(cherry picked from commit 7d6287a8481242cb0f324a2937258f240036dd17)
Signed-off-by: Koba Ko <koba.ko at canonical.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 3132cfebb695..6f525fdd9eb1 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -3695,6 +3695,18 @@ bool intel_dp_initial_fastset_check(struct intel_encoder *encoder,
 				    struct intel_crtc_state *crtc_state)
 {
 	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
+	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
+
+	/*
+	 * If BIOS has set an unsupported or non-standard link rate for some
+	 * reason force an encoder recompute and full modeset.
+	 */
+	if (intel_dp_rate_index(intel_dp->source_rates, intel_dp->num_source_rates,
+				crtc_state->port_clock) < 0) {
+		drm_dbg_kms(&i915->drm, "Forcing full modeset due to unsupported link rate\n");
+		crtc_state->uapi.connectors_changed = true;
+		return false;
+	}
 
 	/*
 	 * FIXME hack to force full modeset when DSC is being used.
-- 
2.25.1