[PATCH v7 09/13] drm/i915/psr: Remove DSB_SKIP_WAITS_EN chicken bit

["Jouni Högander" <jouni.hogander@intel.com>]

We have different approach on how flip is considered being complete. We are
waiting for vblank on DSB and generate interrupt when it happens and this
interrupt is considered as indication of completion -> we definitely do not
want to skip vblank wait.

Also not skipping scanline wait shouldn't cause any problems if we are in
DEEP_SLEEP PIPEDSL register is returning 0 -> evasion does nothing and if
we are not in DEEP_SLEEP evasion works same way as without PSR.

v2: add comment explaining why we are not setting DSB_SKIP_WAITS_EN

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_dsb.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c b/drivers/gpu/drm/i915/display/intel_dsb.c
index 2f2812c23972..30782ab0b908 100644
--- a/drivers/gpu/drm/i915/display/intel_dsb.c
+++ b/drivers/gpu/drm/i915/display/intel_dsb.c
@@ -164,17 +164,26 @@ static int dsb_scanline_to_hw(struct intel_atomic_state *state,
 	return (scanline + vtotal - intel_crtc_scanline_offset(crtc_state)) % vtotal;
 }
 
+/*
+ * Bspec suggests that we should always set DSB_SKIP_WAITS_EN. We have approach
+ * different from what is explained in Bspec on how flip is considered being
+ * complete. We are waiting for vblank in DSB and generate interrupt when it
+ * happens and this interrupt is considered as indication of completion -> we
+ * definitely do not want to skip vblank wait. We also have concern what comes
+ * to skipping vblank evasion. I.e. arming registers are latched before we have
+ * managed writing them. Due to these reasons we are not setting
+ * DSB_SKIP_WAITS_EN.
+ */
 static u32 dsb_chicken(struct intel_atomic_state *state,
 		       struct intel_crtc *crtc)
 {
 	if (pre_commit_is_vrr_active(state, crtc))
-		return DSB_SKIP_WAITS_EN |
-			DSB_CTRL_WAIT_SAFE_WINDOW |
+		return DSB_CTRL_WAIT_SAFE_WINDOW |
 			DSB_CTRL_NO_WAIT_VBLANK |
 			DSB_INST_WAIT_SAFE_WINDOW |
 			DSB_INST_NO_WAIT_VBLANK;
 	else
-		return DSB_SKIP_WAITS_EN;
+		return 0;
 }
 
 static bool assert_dsb_has_room(struct intel_dsb *dsb)
-- 
2.43.0