drm/panfrost: Replace fdinfo's profiling debugfs knob with sysfs

Debugfs isn't always available in production builds that try to squeeze
every single byte out of the kernel image, but we still need a way to
toggle the timestamp and cycle counter registers so that jobs can be
profiled for fdinfo's drm engine and cycle calculations.

Drop the debugfs knob and replace it with a sysfs file that accomplishes
the same functionality, and document its ABI in a separate file.
Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240306015819.822128-2-adrian.larumbe@collabora.com

Documentation/ABI/testing/sysfs-driver-panfrost-profiling

+What:		/sys/bus/platform/drivers/panfrost/.../profiling
+Date:		February 2024
+KernelVersion:	6.8.0
+Contact:	Adrian Larumbe <adrian.larumbe@collabora.com>
+Description:
+		Get/set drm fdinfo's engine and cycles profiling status.
+		Valid values are:
+		0: Don't enable fdinfo job profiling sources.
+		1: Enable fdinfo job profiling sources, this enables both the GPU's
+		   timestamp and cycle counter registers.
\ No newline at end of file

Documentation/gpu/panfrost.rst

@@ -38,3 +38,12 @@ the currently possible format options:
 
 Possible `drm-engine-` key names are: `fragment`, and  `vertex-tiler`.
 `drm-curfreq-` values convey the current operating frequency for that engine.
+
+Users must bear in mind that engine and cycle sampling are disabled by default,
+because of power saving concerns. `fdinfo` users and benchmark applications which
+query the fdinfo file must make sure to toggle the job profiling status of the
+driver by writing into the appropriate sysfs node::
+
+    echo <N> > /sys/bus/platform/drivers/panfrost/[a-f0-9]*.gpu/profiling
+
+Where `N` is either `0` or `1`, depending on the desired enablement status.

drivers/gpu/drm/panfrost/Makefile

@@ -12,6 +12,4 @@ panfrost-y := \
 	panfrost_perfcnt.o \
 	panfrost_dump.o
 
-panfrost-$(CONFIG_DEBUG_FS) += panfrost_debugfs.o
-
 obj-$(CONFIG_DRM_PANFROST) += panfrost.o

drivers/gpu/drm/panfrost/panfrost_debugfs.c

-// SPDX-License-Identifier: GPL-2.0
-/* Copyright 2023 Collabora ltd. */
-/* Copyright 2023 Amazon.com, Inc. or its affiliates. */
-
-#include <linux/debugfs.h>
-#include <linux/platform_device.h>
-#include <drm/drm_debugfs.h>
-#include <drm/drm_file.h>
-#include <drm/panfrost_drm.h>
-
-#include "panfrost_device.h"
-#include "panfrost_gpu.h"
-#include "panfrost_debugfs.h"
-
-void panfrost_debugfs_init(struct drm_minor *minor)
-{
-	struct drm_device *dev = minor->dev;
-	struct panfrost_device *pfdev = platform_get_drvdata(to_platform_device(dev->dev));
-
-	debugfs_create_atomic_t("profile", 0600, minor->debugfs_root, &pfdev->profile_mode);
-}

drivers/gpu/drm/panfrost/panfrost_debugfs.h

-/* SPDX-License-Identifier: GPL-2.0 */
-/*
- * Copyright 2023 Collabora ltd.
- * Copyright 2023 Amazon.com, Inc. or its affiliates.
- */
-
-#ifndef PANFROST_DEBUGFS_H
-#define PANFROST_DEBUGFS_H
-
-#ifdef CONFIG_DEBUG_FS
-void panfrost_debugfs_init(struct drm_minor *minor);
-#endif
-
-#endif  /* PANFROST_DEBUGFS_H */

drivers/gpu/drm/panfrost/panfrost_device.h

@@ -130,7 +130,7 @@ struct panfrost_device {
 	struct list_head scheduled_jobs;
 
 	struct panfrost_perfcnt *perfcnt;
-	atomic_t profile_mode;
+	bool profile_mode;
 
 	struct mutex sched_lock;
 

drivers/gpu/drm/panfrost/panfrost_drv.c

@@ -20,7 +20,6 @@
 #include "panfrost_job.h"
 #include "panfrost_gpu.h"
 #include "panfrost_perfcnt.h"
-#include "panfrost_debugfs.h"
 
 static bool unstable_ioctls;
 module_param_unsafe(unstable_ioctls, bool, 0600);
@@ -600,10 +599,6 @@ static const struct drm_driver panfrost_drm_driver = {
 
 	.gem_create_object	= panfrost_gem_create_object,
 	.gem_prime_import_sg_table = panfrost_gem_prime_import_sg_table,
-
-#ifdef CONFIG_DEBUG_FS
-	.debugfs_init		= panfrost_debugfs_init,
-#endif
 };
 
 static int panfrost_probe(struct platform_device *pdev)
@@ -692,6 +687,40 @@ static void panfrost_remove(struct platform_device *pdev)
 	drm_dev_put(ddev);
 }
 
+static ssize_t profiling_show(struct device *dev,
+			      struct device_attribute *attr, char *buf)
+{
+	struct panfrost_device *pfdev = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%d\n", pfdev->profile_mode);
+}
+
+static ssize_t profiling_store(struct device *dev,
+			       struct device_attribute *attr,
+			       const char *buf, size_t len)
+{
+	struct panfrost_device *pfdev = dev_get_drvdata(dev);
+	bool value;
+	int err;
+
+	err = kstrtobool(buf, &value);
+	if (err)
+		return err;
+
+	pfdev->profile_mode = value;
+
+	return len;
+}
+
+static DEVICE_ATTR_RW(profiling);
+
+static struct attribute *panfrost_attrs[] = {
+	&dev_attr_profiling.attr,
+	NULL,
+};
+
+ATTRIBUTE_GROUPS(panfrost);
+
 /*
  * The OPP core wants the supply names to be NULL terminated, but we need the
  * correct num_supplies value for regulator core. Hence, we NULL terminate here
@@ -789,6 +818,7 @@ static struct platform_driver panfrost_driver = {
 		.name	= "panfrost",
 		.pm	= pm_ptr(&panfrost_pm_ops),
 		.of_match_table = dt_match,
+		.dev_groups = panfrost_groups,
 	},
 };
 module_platform_driver(panfrost_driver);

drivers/gpu/drm/panfrost/panfrost_job.c

@@ -243,7 +243,7 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
 	subslot = panfrost_enqueue_job(pfdev, js, job);
 	/* Don't queue the job if a reset is in progress */
 	if (!atomic_read(&pfdev->reset.pending)) {
-		if (atomic_read(&pfdev->profile_mode)) {
+		if (pfdev->profile_mode) {
 			panfrost_cycle_counter_get(pfdev);
 			job->is_profiled = true;
 			job->start_time = ktime_get();