[Intel-gfx] [PATCH] drm/i915/icl: Add warn about unsupported CDCLK rates

[Imre Deak]

While checking workarounds related to the CDCLK PLL, I noticed that the
DMC firmware bits for WA#1183 are missing for SKL. After that I
clarified with HW people that it's not needed on SKL, since it doesn't
support eDP1.4 which would be the only thing requiring the problematic
CDCLK clock rates. So in theory we shouldn't ever choose these
frequencies, but add an assert in any case for catching such cases and
for documentation.

Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/intel_cdclk.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_cdclk.c b/drivers/gpu/drm/i915/intel_cdclk.c
index 704ddb4d3ca7..71045c38e233 100644
--- a/drivers/gpu/drm/i915/intel_cdclk.c
+++ b/drivers/gpu/drm/i915/intel_cdclk.c
@@ -2355,6 +2355,16 @@ static int skl_modeset_calc_cdclk(struct drm_atomic_state *state)
 	 */
 	cdclk = skl_calc_cdclk(min_cdclk, vco);
 
+	/*
+	 * The following CDCLK rates are unsupported on SKL. In theory this
+	 * should never happen since only the eDP1.4 2.16 and 4.32Gbps rates
+	 * require it, but eDP1.4 is not supported on SKL, see display
+	 * WA#1183.
+	 */
+	if (IS_SKYLAKE(to_i915(state->dev)) &&
+	    (cdclk == 308571 || cdclk == 617143))
+		DRM_WARN_ONCE("Unsupported CDCLK rate.\n");
+
 	intel_state->cdclk.logical.vco = vco;
 	intel_state->cdclk.logical.cdclk = cdclk;
 	intel_state->cdclk.logical.voltage_level =
-- 
2.13.2