drm/i915/mtl: Synchronize i915/BIOS on C6 enabling

If BIOS enables/disables C6, i915 should do the same. Also, retain
this value across driver reloads. This is needed only for MTL as
of now due to an existing bug in OA which needs C6 disabled for
it to function. BIOS behavior is also different across platforms
in terms of how C6 is enabled.
Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323225901.3743681-3-umesh.nerlige.ramappa@intel.com

drivers/gpu/drm/i915/gt/intel_rc6.c

@@ -420,6 +420,21 @@ static void vlv_rc6_enable(struct intel_rc6 *rc6)
 	    GEN7_RC_CTL_TO_MODE | VLV_RC_CTL_CTX_RST_PARALLEL;
 }
 
+bool intel_check_bios_c6_setup(struct intel_rc6 *rc6)
+{
+	if (!rc6->bios_state_captured) {
+		struct intel_uncore *uncore = rc6_to_uncore(rc6);
+		intel_wakeref_t wakeref;
+
+		with_intel_runtime_pm(uncore->rpm, wakeref)
+			rc6->bios_rc_state = intel_uncore_read(uncore, GEN6_RC_STATE);
+
+		rc6->bios_state_captured = true;
+	}
+
+	return rc6->bios_rc_state & RC_SW_TARGET_STATE_MASK;
+}
+
 static bool bxt_check_bios_rc6_setup(struct intel_rc6 *rc6)
 {
 	struct intel_uncore *uncore = rc6_to_uncore(rc6);
@@ -503,10 +518,10 @@ static bool rc6_supported(struct intel_rc6 *rc6)
 		return false;
 	}
 
-	if (IS_MTL_MEDIA_STEP(gt->i915, STEP_A0, STEP_B0) &&
-	    gt->type == GT_MEDIA) {
+	if (IS_METEORLAKE(gt->i915) &&
+	    !intel_check_bios_c6_setup(rc6)) {
 		drm_notice(&i915->drm,
-			   "Media RC6 disabled on A step\n");
+			   "C6 disabled by BIOS\n");
 		return false;
 	}
 
@@ -707,9 +722,14 @@ void intel_rc6_disable(struct intel_rc6 *rc6)
 void intel_rc6_fini(struct intel_rc6 *rc6)
 {
 	struct drm_i915_gem_object *pctx;
+	struct intel_uncore *uncore = rc6_to_uncore(rc6);
 
 	intel_rc6_disable(rc6);
 
+	/* We want the BIOS C6 state preserved across loads for MTL */
+	if (IS_METEORLAKE(rc6_to_i915(rc6)) && rc6->bios_state_captured)
+		set(uncore, GEN6_RC_STATE, rc6->bios_rc_state);
+
 	pctx = fetch_and_zero(&rc6->pctx);
 	if (pctx)
 		i915_gem_object_put(pctx);

drivers/gpu/drm/i915/gt/intel_rc6.h

@@ -27,4 +27,6 @@ u64 intel_rc6_residency_us(struct intel_rc6 *rc6, enum intel_rc6_res_type id);
 void intel_rc6_print_residency(struct seq_file *m, const char *title,
 			       enum intel_rc6_res_type id);
 
+bool intel_check_bios_c6_setup(struct intel_rc6 *rc6);
+
 #endif /* INTEL_RC6_H */

drivers/gpu/drm/i915/gt/intel_rc6_types.h

@@ -29,6 +29,7 @@ struct intel_rc6 {
 	u64 cur_residency[INTEL_RC6_RES_MAX];
 
 	u32 ctl_enable;
+	u32 bios_rc_state;
 
 	struct drm_i915_gem_object *pctx;
 
@@ -36,6 +37,7 @@ struct intel_rc6 {
 	bool enabled : 1;
 	bool manual : 1;
 	bool wakeref : 1;
+	bool bios_state_captured : 1;
 };
 
 #endif /* INTEL_RC6_TYPES_H */