drm/i915/vrr: Add compute config for DC Balance params

Compute DC Balance parameters and tunable params based on
experiments.

--v2:
- Document tunable params. (Ankit)

--v3:
- Add line spaces to compute config. (Ankit)
- Remove redundancy checks.

--v4:
- Separate out conpute config to separate function.
- As all the valuse are being computed in scanlines, and slope
is still in usec, convert and store it to scanlines.

--v5:
- Update and add comments for slope calculation. (Ankit)
- Update early return conditions for dc balance compute. (Ankit)

--v6:
- Early return condition simplified for dc balance compute config. (Ankit)
- Make use of pipe restrictions to this patch. (Ankit)

--v7:
- Separate out PIPE_A and PIPE_B restrictions to other patch.(Ankit)

Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patch.msgid.link/20251223104542.2688548-8-mitulkumar.ajitkumar.golani@intel.com

1 files changed, 45 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
index 427ef1741051..952e3c31bacc 100644
--- a/drivers/gpu/drm/i915/display/intel_vrr.c
+++ b/drivers/gpu/drm/i915/display/intel_vrr.c
@@ -6,6 +6,7 @@
 
 #include <drm/drm_print.h>
 
+#include "intel_crtc.h"
 #include "intel_de.h"
 #include "intel_display_regs.h"
 #include "intel_display_types.h"
@@ -20,6 +21,14 @@
 #define FIXED_POINT_PRECISION		100
 #define CMRR_PRECISION_TOLERANCE	10
 
+/*
+ * Tunable parameters for DC Balance correction.
+ * These are captured based on experimentations.
+ */
+#define DCB_CORRECTION_SENSITIVITY	30
+#define DCB_CORRECTION_AGGRESSIVENESS	1000 /* ms × 100; 10 ms */
+#define DCB_BLANK_TARGET		50
+
 bool intel_vrr_is_capable(struct intel_connector *connector)
 {
 	struct intel_display *display = to_intel_display(connector);
@@ -342,6 +351,40 @@ int intel_vrr_compute_vmax(struct intel_connector *connector,
 	return vmax;
 }
 
+static void
+intel_vrr_dc_balance_compute_config(struct intel_crtc_state *crtc_state)
+{
+	int guardband_usec, adjustment_usec;
+	struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
+
+	if (!HAS_VRR_DC_BALANCE(display) || !crtc_state->vrr.enable)
+		return;
+
+	crtc_state->vrr.dc_balance.vmax = crtc_state->vrr.vmax;
+	crtc_state->vrr.dc_balance.vmin = crtc_state->vrr.vmin;
+	crtc_state->vrr.dc_balance.max_increase =
+		crtc_state->vrr.vmax - crtc_state->vrr.vmin;
+	crtc_state->vrr.dc_balance.max_decrease =
+		crtc_state->vrr.vmax - crtc_state->vrr.vmin;
+	crtc_state->vrr.dc_balance.guardband =
+		DIV_ROUND_UP(crtc_state->vrr.dc_balance.vmax *
+			     DCB_CORRECTION_SENSITIVITY, 100);
+	guardband_usec =
+		intel_scanlines_to_usecs(adjusted_mode,
+					 crtc_state->vrr.dc_balance.guardband);
+	/*
+	 *  The correction_aggressiveness/100 is the number of milliseconds to
+	 *  adjust by when the balance is at twice the guardband.
+	 *  guardband_slope = correction_aggressiveness / (guardband * 100)
+	 */
+	adjustment_usec = DCB_CORRECTION_AGGRESSIVENESS * 10;
+	crtc_state->vrr.dc_balance.slope =
+		DIV_ROUND_UP(adjustment_usec, guardband_usec);
+	crtc_state->vrr.dc_balance.vblank_target =
+		DIV_ROUND_UP((crtc_state->vrr.vmax - crtc_state->vrr.vmin) *
+			     DCB_BLANK_TARGET, 100);
+}
+
 void
 intel_vrr_compute_config(struct intel_crtc_state *crtc_state,
 			 struct drm_connector_state *conn_state)
@@ -399,6 +442,8 @@ intel_vrr_compute_config(struct intel_crtc_state *crtc_state,
 			(crtc_state->hw.adjusted_mode.crtc_vtotal -
 			 crtc_state->hw.adjusted_mode.crtc_vsync_end);
 	}
+
+	intel_vrr_dc_balance_compute_config(crtc_state);
 }
 
 static int