drm/i915/pc8: Add parent interface for PC8 forcewake tricks

We use forcewake to prevent the SoC from actually entering
PC8 while performing the PC8 disable sequence. Hide that
behind a new parent interface to eliminate the naked
forcewake/uncore usage from the display power code.

v2: Mark the interface optional and warn if
    someone calls it when not provided (Jani)
    Include the header to make sure the extern
    declaration matches the definition (Jani)
v3: Rebase due to shuffling

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20251218182052.18756-1-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/Makefile

@@ -76,6 +76,7 @@ i915-$(CONFIG_PERF_EVENTS) += \
 
 # core display adaptation
 i915-y += \
+	i915_display_pc8.o \
 	i915_hdcp_gsc.o \
 	i915_panic.o
 

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

@@ -1339,10 +1339,10 @@ static void hsw_restore_lcpll(struct intel_display *display)
 		return;
 
 	/*
-	 * Make sure we're not on PC8 state before disabling PC8, otherwise
+	 * Make sure we're not on PC8 state before disabling
-	 * we'll hang the machine. To prevent PC8 state, just enable force_wake.
+	 * PC8, otherwise we'll hang the machine.
 	 */
-	intel_uncore_forcewake_get(&dev_priv->uncore, FORCEWAKE_ALL);
+	intel_parent_pc8_block(display);
 
 	if (val & LCPLL_POWER_DOWN_ALLOW) {
 		val &= ~LCPLL_POWER_DOWN_ALLOW;
@@ -1372,7 +1372,7 @@ static void hsw_restore_lcpll(struct intel_display *display)
 				"Switching back to LCPLL failed\n");
 	}
 
-	intel_uncore_forcewake_put(&dev_priv->uncore, FORCEWAKE_ALL);
+	intel_parent_pc8_unblock(display);
 
 	intel_update_cdclk(display);
 	intel_cdclk_dump_config(display, &display->cdclk.hw, "Current CDCLK");

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

@@ -75,6 +75,23 @@ void intel_parent_panic_finish(struct intel_display *display, struct intel_panic
 	display->parent->panic->finish(panic);
 }
 
+/* pc8 */
+void intel_parent_pc8_block(struct intel_display *display)
+{
+	if (drm_WARN_ON_ONCE(display->drm, !display->parent->pc8))
+		return;
+
+	display->parent->pc8->block(display->drm);
+}
+
+void intel_parent_pc8_unblock(struct intel_display *display)
+{
+	if (drm_WARN_ON_ONCE(display->drm, !display->parent->pc8))
+		return;
+
+	display->parent->pc8->unblock(display->drm);
+}
+
 /* rps */
 bool intel_parent_rps_available(struct intel_display *display)
 {

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

@@ -32,6 +32,10 @@ struct intel_panic *intel_parent_panic_alloc(struct intel_display *display);
 int intel_parent_panic_setup(struct intel_display *display, struct intel_panic *panic, struct drm_scanout_buffer *sb);
 void intel_parent_panic_finish(struct intel_display *display, struct intel_panic *panic);
 
+/* pc8 */
+void intel_parent_pc8_block(struct intel_display *display);
+void intel_parent_pc8_unblock(struct intel_display *display);
+
 /* rps */
 bool intel_parent_rps_available(struct intel_display *display);
 void intel_parent_rps_boost_if_not_started(struct intel_display *display, struct dma_fence *fence);

drivers/gpu/drm/i915/i915_display_pc8.c

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright 2025, Intel Corporation.
+ */
+
+#include <drm/drm_print.h>
+#include <drm/intel/display_parent_interface.h>
+
+#include "i915_display_pc8.h"
+#include "i915_drv.h"
+#include "intel_uncore.h"
+
+static void i915_display_pc8_block(struct drm_device *drm)
+{
+	struct intel_uncore *uncore = &to_i915(drm)->uncore;
+
+	/* to prevent PC8 state, just enable force_wake */
+	intel_uncore_forcewake_get(uncore, FORCEWAKE_ALL);
+}
+
+static void i915_display_pc8_unblock(struct drm_device *drm)
+{
+	struct intel_uncore *uncore = &to_i915(drm)->uncore;
+
+	intel_uncore_forcewake_put(uncore, FORCEWAKE_ALL);
+}
+
+const struct intel_display_pc8_interface i915_display_pc8_interface = {
+	.block = i915_display_pc8_block,
+	.unblock = i915_display_pc8_unblock,
+};

drivers/gpu/drm/i915/i915_display_pc8.h

@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: MIT */
+/* Copyright © 2025 Intel Corporation */
+
+#ifndef __I915_DISPLAY_PC8_H__
+#define __I915_DISPLAY_PC8_H__
+
+extern const struct intel_display_pc8_interface i915_display_pc8_interface;
+
+#endif /* __I915_DISPLAY_PC8_H__ */

drivers/gpu/drm/i915/i915_driver.c

@@ -89,6 +89,7 @@
 #include "pxp/intel_pxp_pm.h"
 
 #include "i915_debugfs.h"
+#include "i915_display_pc8.h"
 #include "i915_driver.h"
 #include "i915_drm_client.h"
 #include "i915_drv.h"
@@ -765,6 +766,7 @@ static const struct intel_display_parent_interface parent = {
 	.hdcp = &i915_display_hdcp_interface,
 	.irq = &i915_display_irq_interface,
 	.panic = &i915_display_panic_interface,
+	.pc8 = &i915_display_pc8_interface,
 	.rpm = &i915_display_rpm_interface,
 	.rps = &i915_display_rps_interface,
 	.stolen = &i915_display_stolen_interface,

include/drm/intel/display_parent_interface.h

@@ -36,6 +36,11 @@ struct intel_display_panic_interface {
 	void (*finish)(struct intel_panic *panic);
 };
 
+struct intel_display_pc8_interface {
+	void (*block)(struct drm_device *drm);
+	void (*unblock)(struct drm_device *drm);
+};
+
 struct intel_display_rpm_interface {
 	struct ref_tracker *(*get)(const struct drm_device *drm);
 	struct ref_tracker *(*get_raw)(const struct drm_device *drm);
@@ -96,6 +101,9 @@ struct intel_display_parent_interface {
 	/** @panic: Panic interface */
 	const struct intel_display_panic_interface *panic;
 
+	/** @pc8: PC8 interface. Optional. */
+	const struct intel_display_pc8_interface *pc8;
+
 	/** @rpm: Runtime PM functions */
 	const struct intel_display_rpm_interface *rpm;