drm/vc4: Leverage the load tracker on the BCM2711

The load tracker was initially designed to report and warn about a load
too high for the HVS. To do so, it computes for each plane the impact
it's going to have on the HVS, and will warn (if it's enabled) if we go
over what the hardware can process.

While the limits being used are a bit irrelevant to the BCM2711, the
algorithm to compute the HVS load will be one component used in order to
compute the core clock rate on the BCM2711.

Let's remove the hooks to prevent the load tracker to do its
computation, but since we don't have the same limits, don't check them
against them, and prevent the debugfs file to enable it from being
created.
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20211025152903.1088803-8-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_debugfs.c

@@ -7,6 +7,7 @@
 #include <linux/circ_buf.h>
 #include <linux/ctype.h>
 #include <linux/debugfs.h>
+#include <linux/platform_device.h>
 
 #include "vc4_drv.h"
 #include "vc4_regs.h"
@@ -26,8 +27,10 @@ vc4_debugfs_init(struct drm_minor *minor)
 	struct vc4_dev *vc4 = to_vc4_dev(minor->dev);
 	struct vc4_debugfs_info_entry *entry;
 
-	debugfs_create_bool("hvs_load_tracker", S_IRUGO | S_IWUSR,
-			    minor->debugfs_root, &vc4->load_tracker_enabled);
+	if (!of_device_is_compatible(vc4->hvs->pdev->dev.of_node,
+				     "brcm,bcm2711-vc5"))
+		debugfs_create_bool("hvs_load_tracker", S_IRUGO | S_IWUSR,
+				    minor->debugfs_root, &vc4->load_tracker_enabled);
 
 	list_for_each_entry(entry, &vc4->debugfs_list, link) {
 		drm_debugfs_create_files(&entry->info, 1,

drivers/gpu/drm/vc4/vc4_drv.h

@@ -202,9 +202,6 @@ struct vc4_dev {
 
 	int power_refcount;
 
-	/* Set to true when the load tracker is supported. */
-	bool load_tracker_available;
-
 	/* Set to true when the load tracker is active. */
 	bool load_tracker_enabled;
 

drivers/gpu/drm/vc4/vc4_kms.c

@@ -551,9 +551,6 @@ static int vc4_load_tracker_atomic_check(struct drm_atomic_state *state)
 	struct drm_plane *plane;
 	int i;
 
-	if (!vc4->load_tracker_available)
-		return 0;
-
 	priv_state = drm_atomic_get_private_obj_state(state,
 						      &vc4->load_tracker);
 	if (IS_ERR(priv_state))
@@ -628,9 +625,6 @@ static void vc4_load_tracker_obj_fini(struct drm_device *dev, void *unused)
 {
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 
-	if (!vc4->load_tracker_available)
-		return;
-
 	drm_atomic_private_obj_fini(&vc4->load_tracker);
 }
 
@@ -638,9 +632,6 @@ static int vc4_load_tracker_obj_init(struct vc4_dev *vc4)
 {
 	struct vc4_load_tracker_state *load_state;
 
-	if (!vc4->load_tracker_available)
-		return 0;
-
 	load_state = kzalloc(sizeof(*load_state), GFP_KERNEL);
 	if (!load_state)
 		return -ENOMEM;
@@ -868,9 +859,12 @@ int vc4_kms_load(struct drm_device *dev)
 					      "brcm,bcm2711-vc5");
 	int ret;
 
+	/*
+	 * The limits enforced by the load tracker aren't relevant for
+	 * the BCM2711, but the load tracker computations are used for
+	 * the core clock rate calculation.
+	 */
 	if (!is_vc5) {
-		vc4->load_tracker_available = true;
-
 		/* Start with the load tracker enabled. Can be
 		 * disabled through the debugfs load_tracker file.
 		 */

drivers/gpu/drm/vc4/vc4_plane.c

@@ -529,11 +529,6 @@ static void vc4_plane_calc_load(struct drm_plane_state *state)
 	struct vc4_plane_state *vc4_state;
 	struct drm_crtc_state *crtc_state;
 	unsigned int vscale_factor;
-	struct vc4_dev *vc4;
-
-	vc4 = to_vc4_dev(state->plane->dev);
-	if (!vc4->load_tracker_available)
-		return;
 
 	vc4_state = to_vc4_plane_state(state);
 	crtc_state = drm_atomic_get_existing_crtc_state(state->state,