[PATCH] drm/i915/cnl: Mask previous DDI - PLL mapping

[James Ausmus <james.ausmus@intel.com>]

Without masking out the old value, we can end up pointing the DDI to a
disabled PLL, which makes the system fall over. Mask out the previous
value before setting the PLL to DDI mapping.

This can be observed by running igt/testdisplay with both an eDP and
HDMI/DP output active.

Fixes: 555e38d273172 ("drm/i915/cnl: DDI - PLL mapping")
Testcase: igt/testdisplay
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Matt Atwood <matthew.s.atwood@intel.com>
Signed-off-by: James Ausmus <james.ausmus@intel.com>
---
 drivers/gpu/drm/i915/intel_ddi.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index eff3b51872eb..123a3253453f 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -2098,6 +2098,7 @@ static void intel_ddi_clk_select(struct intel_encoder *encoder,
 	if (IS_CANNONLAKE(dev_priv)) {
 		/* Configure DPCLKA_CFGCR0 to map the DPLL to the DDI. */
 		val = I915_READ(DPCLKA_CFGCR0);
+		val &= ~DPCLKA_CFGCR0_DDI_CLK_SEL_MASK(port);
 		val |= DPCLKA_CFGCR0_DDI_CLK_SEL(pll->id, port);
 		I915_WRITE(DPCLKA_CFGCR0, val);
 
-- 
2.15.1

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