drm/i915/flipq: Implement Wa_18034343758

Implement the driver side of Wa_18034343758, which is supposed to
prevent the DSB and DMC from accessing registers in parallel, and
thus potentially corrupting the registers due to a hardware issue
(which should be fixed in PTL-B0).

The w/a sequence goes as follows:
DMC starts the DSB
 |                 \
DMC halts itself    | DSB waits a while for DMC to have time to halt
 .                  | DSB executes normally
 .		    | DSB unhalts the DMC at the very end
 .             	   /
DMC resumes execution

v2: PTL-B0+ firmware no longer has the w/a since the hw got fixed
v3: Do the w/a on all PTL for now since we only have the A0 firmware
    binaries which issues the halt instructions unconditionally
v4: PTL DMC binaries do in fact have the A0 vs. B0 split, so skip
    the w/a on PTL-B0+

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/20250624170049.27284-7-ville.syrjala@linux.intel.com

Author: vsyrjala

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

@@ -7246,6 +7246,10 @@ static void intel_atomic_dsb_finish(struct intel_atomic_state *state,
 	}
 
 	if (new_crtc_state->use_flipq || new_crtc_state->use_dsb) {
+		/* Wa_18034343758 */
+		if (new_crtc_state->use_flipq)
+			intel_flipq_wait_dmc_halt(new_crtc_state->dsb_commit, crtc);
+
 		if (intel_crtc_needs_color_update(new_crtc_state))
 			intel_color_commit_noarm(new_crtc_state->dsb_commit,
 						 new_crtc_state);
@@ -7276,6 +7280,10 @@ static void intel_atomic_dsb_finish(struct intel_atomic_state *state,
 		if (DISPLAY_VER(display) >= 9)
 			skl_detach_scalers(new_crtc_state->dsb_commit,
 					   new_crtc_state);
+
+		/* Wa_18034343758 */
+		if (new_crtc_state->use_flipq)
+			intel_flipq_unhalt_dmc(new_crtc_state->dsb_commit, crtc);
 	}
 
 	if (intel_color_uses_chained_dsb(new_crtc_state))

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

@@ -400,3 +400,27 @@ void intel_flipq_add(struct intel_crtc *crtc,
 
 	intel_flipq_sw_dmc_wake(crtc);
 }
+
+/* Wa_18034343758 */
+static bool need_dmc_halt_wa(struct intel_display *display)
+{
+	return DISPLAY_VER(display) == 20 ||
+		(display->platform.pantherlake &&
+		 IS_DISPLAY_STEP(display, STEP_A0, STEP_B0));
+}
+
+void intel_flipq_wait_dmc_halt(struct intel_dsb *dsb, struct intel_crtc *crtc)
+{
+	struct intel_display *display = to_intel_display(crtc);
+
+	if (need_dmc_halt_wa(display))
+		intel_dsb_wait_usec(dsb, 2);
+}
+
+void intel_flipq_unhalt_dmc(struct intel_dsb *dsb, struct intel_crtc *crtc)
+{
+	struct intel_display *display = to_intel_display(crtc);
+
+	if (need_dmc_halt_wa(display))
+		intel_dsb_reg_write(dsb, PIPEDMC_CTL(crtc->pipe), 0);
+}

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

@@ -29,5 +29,7 @@ void intel_flipq_add(struct intel_crtc *crtc,
 		     enum intel_dsb_id dsb_id,
 		     struct intel_dsb *dsb);
 int intel_flipq_exec_time_us(struct intel_display *display);
+void intel_flipq_wait_dmc_halt(struct intel_dsb *dsb, struct intel_crtc *crtc);
+void intel_flipq_unhalt_dmc(struct intel_dsb *dsb, struct intel_crtc *crtc);
 
 #endif /* __INTEL_FLIPQ_H__ */