[PATCH 3/8] drm/i915/vblank: Add helper to get correct vblank length

[Ankit Nautiyal <ankit.k.nautiyal@intel.com>]

Currently crtc_vblank_start is assumed to be the vblank_start for the fixed
refresh rate case. That value can be different from the variable refresh
rate case whenever always_use_vrr_tg()==false. On icl/tgl it's always
different due to the extra vblank delay, and also on adl+ it could be
different if we were to use an optimized guardband.

So places where crtc_vblank_start is used to compute vblank length needs
change so as to account for cases where vrr is enabled. Specifically
with vrr.enable the effective vblank length is actually guardband.

Add a helper to get the correct vblank length for both vrr and fixed
refresh rate cases. Use this helper where vblank_start is used to
compute the vblank length.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
---
 drivers/gpu/drm/i915/display/intel_vblank.c  | 10 ++++++++++
 drivers/gpu/drm/i915/display/intel_vblank.h  |  2 ++
 drivers/gpu/drm/i915/display/skl_watermark.c |  3 ++-
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c b/drivers/gpu/drm/i915/display/intel_vblank.c
index 0b7fcc05e64c..2fc0c1c0bb87 100644
--- a/drivers/gpu/drm/i915/display/intel_vblank.c
+++ b/drivers/gpu/drm/i915/display/intel_vblank.c
@@ -767,3 +767,13 @@ int intel_vblank_evade(struct intel_vblank_evade_ctx *evade)
 
 	return scanline;
 }
+
+int intel_crtc_vblank_length(const struct intel_crtc_state *crtc_state)
+{
+	const struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
+
+	if (crtc_state->vrr.enable)
+		return crtc_state->vrr.guardband;
+	else
+		return adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
+}
diff --git a/drivers/gpu/drm/i915/display/intel_vblank.h b/drivers/gpu/drm/i915/display/intel_vblank.h
index 21fbb08d61d5..98d04cacd65f 100644
--- a/drivers/gpu/drm/i915/display/intel_vblank.h
+++ b/drivers/gpu/drm/i915/display/intel_vblank.h
@@ -48,4 +48,6 @@ const struct intel_crtc_state *
 intel_pre_commit_crtc_state(struct intel_atomic_state *state,
 			    struct intel_crtc *crtc);
 
+int intel_crtc_vblank_length(const struct intel_crtc_state *crtc_state);
+
 #endif /* __INTEL_VBLANK_H__ */
diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
index 9df9ee137bf9..06e5e6c77d2e 100644
--- a/drivers/gpu/drm/i915/display/skl_watermark.c
+++ b/drivers/gpu/drm/i915/display/skl_watermark.c
@@ -28,6 +28,7 @@
 #include "intel_flipq.h"
 #include "intel_pcode.h"
 #include "intel_plane.h"
+#include "intel_vblank.h"
 #include "intel_wm.h"
 #include "skl_universal_plane_regs.h"
 #include "skl_watermark.h"
@@ -2241,7 +2242,7 @@ skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
 		scaler_prefill_latency(crtc_state) +
 		dsc_prefill_latency(crtc_state) +
 		wm0_lines >
-		adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
+		intel_crtc_vblank_length(crtc_state);
 }
 
 static int skl_max_wm0_lines(const struct intel_crtc_state *crtc_state)
-- 
2.45.2