[Bug 91697] [SKL, BIOS upgrade regression] distorted display after resume from suspend

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91697

--- Comment #21 from Akshu Agrawal <akshu.agrawal at intel.com> ---
If we just enable the ‘DBUF Power Request’ bit in DBUF_CNTL, there is no
display corruption. IMO this bit is left in reset state as we are enabling the
PW2 in BIOS. Following change would also fix the issue:

diff --git a/drivers/gpu/drm/i915/intel_display.c
b/drivers/gpu/drm/i915/intel_display.c
index af0bcfe..fd69c4c 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5698,6 +5698,12 @@ void skl_init_cdclk(struct drm_i915_private *dev_priv)
        /* DPLL0 already enabed !? */
        if (I915_READ(LCPLL1_CTL) & LCPLL_PLL_ENABLE) {
                DRM_DEBUG_DRIVER("DPLL0 already running\n");
+               /* check for DBUF status and enable if in reset state */
+               if (!(I915_READ(DBUF_CTL) & DBUF_POWER_STATE)) {
+                       I915_WRITE(DBUF_CTL, I915_READ(DBUF_CTL)
+                                       | DBUF_POWER_REQUEST);
+                       POSTING_READ(DBUF_CTL);
+               }
                return;
        }

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