[PATCH v3] drm/i915/display: Use the recomended min_hblank values

[Arun R Murthy]

Use recommended values as per wa_14021694213 to compare with the
calculated value and choose minimum of them.

v2: corrected checkpatch warning and retain the restriction for
min_hblank (Jani)
v3: use calculated value to compare with recomended value and choose
minimum of them (Imre)

Bspec: 74379
Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
---
Changes in v3:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v2: https://lore.kernel.org/r/20250624-min_hblank-v2-1-9110a9342d8c@intel.com

Changes in v2:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v1: https://lore.kernel.org/r/20250624-min_hblank-v1-1-5c100e4a8b05@intel.com
---
 drivers/gpu/drm/i915/display/intel_dp.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index f48912f308df7fd26c9d089e8f1bd096bfc8df95..c55315fb74734fded40695bae40dd19f71a9786f 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -3175,7 +3175,22 @@ int intel_dp_compute_min_hblank(struct intel_crtc_state *crtc_state,
 	 */
 	min_hblank = min_hblank - 2;
 
-	min_hblank = min(10, min_hblank);
+	/*
+	 * min_hblank formula is undergoing a change, to avoid underrun use the
+	 * recomended value in spec to compare with the calculated one and use the
+	 * minimum value
+	 */
+	if (intel_dp_is_uhbr(crtc_state)) {
+		if (crtc_state->dsc.compression_enable &&
+		    crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420 &&
+		    crtc_state->pipe_bpp == 18)
+			min_hblank = min(2, min_hblank);
+		else
+			min_hblank = min(3, min_hblank);
+	} else {
+		min_hblank = min(10, min_hblank);
+	}
+
 	crtc_state->min_hblank = min_hblank;
 
 	return 0;

---
base-commit: da56936fad6f5e1d5f0cef8b50277bfb071eefe7
change-id: 20250624-min_hblank-8af8d2626ff8

Best regards,
-- 
Arun R Murthy <arun.r.murthy at intel.com>