[PATCH 5/5] drm/i915/psr: Wait for PSR transition to complete before exiting.

[Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>]

With fbdev, screen freezes after a few continuous PSR exit->enter cycles.
Printing out the PSR status register clearly showed this freeze coincided
with exiting when the hardware is in a transitory state. So wait for a max
of 100 ms (~6 frames) for PSR to become active and then exit.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
---
 drivers/gpu/drm/i915/intel_psr.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_psr.c b/drivers/gpu/drm/i915/intel_psr.c
index 2a31c7cbdb41..d6669f5f890f 100644
--- a/drivers/gpu/drm/i915/intel_psr.c
+++ b/drivers/gpu/drm/i915/intel_psr.c
@@ -738,6 +738,17 @@ static void intel_psr_exit(struct drm_i915_private *dev_priv)
 			WARN_ON(!(val & EDP_PSR2_ENABLE));
 			I915_WRITE(EDP_PSR2_CTL, val & ~EDP_PSR2_ENABLE);
 		} else {
+			/* Wait for about 6 frames in case we just enabled PSR,
+			 * this prevents the screen from freezing as the HW does
+			 * not seem to be able to back off cleanly it is already
+			 * trying to enter PSR.
+			 */
+			intel_wait_for_register(dev_priv,
+						EDP_PSR_STATUS,
+						EDP_PSR_STATUS_STATE_MASK,
+						EDP_PSR_STATUS_STATE_SRDENT,
+						100);
+
 			val = I915_READ(EDP_PSR_CTL);
 			WARN_ON(!(val & EDP_PSR_ENABLE));
 			I915_WRITE(EDP_PSR_CTL, val & ~EDP_PSR_ENABLE);
-- 
2.14.1

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