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.
v2: Add the Bugzilla link
Fixes: 555e38d273172 ("drm/i915/cnl: DDI - PLL mapping")
Testcase: igt/testdisplay
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103997
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Cc: Matt Atwood <matthew.s.atwood@xxxxxxxxx>
Signed-off-by: James Ausmus <james.ausmus@xxxxxxxxx>
---
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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