drm/i915/dsb: Introduce intel_dsb_exec_time_us()

Pull the magic 20 usec DSB execution deadline into
intel_dsb_arm_exec_time_us(), and also add its counterpart
for the non-arming register write section. For the non-arming
part we'll just throw in a random 80 usec for now so the total
is 100usec. The total exec time will be needed by the upcoming
flip queue code.

Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250612145018.8735-4-ville.syrjala@linux.intel.com

Author: vsyrjala

drivers/gpu/drm/i915/display/intel_dsb.c

@@ -685,14 +685,36 @@ static u32 dsb_error_int_en(struct intel_display *display)
 	return errors;
 }
 
+/*
+ * FIXME calibrate these sensibly, ideally compute based on
+ * the number of regisetrs to be written. But that requires
+ * measuring the actual DSB execution speed on each platform
+ * (and the speed also depends on CDCLK and memory clock)...
+ */
+static int intel_dsb_noarm_exec_time_us(void)
+{
+	return 80;
+}
+
+static int intel_dsb_arm_exec_time_us(void)
+{
+	return 20;
+}
+
+int intel_dsb_exec_time_us(void)
+{
+	return intel_dsb_noarm_exec_time_us() +
+		intel_dsb_arm_exec_time_us();
+}
+
 void intel_dsb_vblank_evade(struct intel_atomic_state *state,
 			    struct intel_dsb *dsb)
 {
 	struct intel_crtc *crtc = dsb->crtc;
 	const struct intel_crtc_state *crtc_state =
 		intel_pre_commit_crtc_state(state, crtc);
-	/* FIXME calibrate sensibly */
-	int latency = intel_usecs_to_scanlines(&crtc_state->hw.adjusted_mode, 20);
+	int latency = intel_usecs_to_scanlines(&crtc_state->hw.adjusted_mode,
+					       intel_dsb_arm_exec_time_us());
 	int start, end;
 
 	/*

drivers/gpu/drm/i915/display/intel_dsb.h

@@ -35,6 +35,7 @@ struct intel_dsb *intel_dsb_prepare(struct intel_atomic_state *state,
 void intel_dsb_finish(struct intel_dsb *dsb);
 void intel_dsb_gosub_finish(struct intel_dsb *dsb);
 void intel_dsb_cleanup(struct intel_dsb *dsb);
+int intel_dsb_exec_time_us(void);
 void intel_dsb_reg_write(struct intel_dsb *dsb,
 			 i915_reg_t reg, u32 val);
 void intel_dsb_reg_write_indexed(struct intel_dsb *dsb,