drm/panthor: add sysfs knob for enabling job profiling

This commit introduces a DRM device sysfs attribute that lets UM control
the job accounting status in the device. The knob variable had been brought
in as part of a previous commit, but now we're able to fix it manually.

As sysfs files are part of a driver's uAPI, describe its legitimate input
values and output format in a documentation file.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240923230912.2207320-6-adrian.larumbe@collabora.com

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

+What:		/sys/bus/platform/drivers/panthor/.../profiling
+Date:		September 2024
+KernelVersion:	6.11.0
+Contact:	Adrian Larumbe <adrian.larumbe@collabora.com>
+Description:
+		Bitmask to enable drm fdinfo's job profiling measurements.
+		Valid values are:
+		0: Don't enable fdinfo job profiling sources.
+		1: Enable GPU cycle measurements for running jobs.
+		2: Enable GPU timestamp sampling for running jobs.

Documentation/gpu/panthor.rst

+.. SPDX-License-Identifier: GPL-2.0+
+
+=========================
+ drm/Panthor CSF driver
+=========================
+
+.. _panfrost-usage-stats:
+
+Panthor DRM client usage stats implementation
+==============================================
+
+The drm/Panthor driver implements the DRM client usage stats specification as
+documented in :ref:`drm-client-usage-stats`.
+
+Example of the output showing the implemented key value pairs and entirety of
+the currently possible format options:
+
+::
+     pos:    0
+     flags:  02400002
+     mnt_id: 29
+     ino:    491
+     drm-driver:     panthor
+     drm-client-id:  10
+     drm-engine-panthor:     111110952750 ns
+     drm-cycles-panthor:     94439687187
+     drm-maxfreq-panthor:    1000000000 Hz
+     drm-curfreq-panthor:    1000000000 Hz
+     drm-total-memory:       16480 KiB
+     drm-shared-memory:      0
+     drm-active-memory:      16200 KiB
+     drm-resident-memory:    16480 KiB
+     drm-purgeable-memory:   0
+
+Possible `drm-engine-` key names are: `panthor`.
+`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/panthor/[a-f0-9]*.gpu/profiling
+
+Where `N` is a bit mask where cycle and timestamp sampling are respectively
+enabled by the first and second bits.

drivers/gpu/drm/panthor/panthor_drv.c

@@ -1536,6 +1536,44 @@ static void panthor_remove(struct platform_device *pdev)
 	panthor_device_unplug(ptdev);
 }
 
+static ssize_t profiling_show(struct device *dev,
+			      struct device_attribute *attr,
+			      char *buf)
+{
+	struct panthor_device *ptdev = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%d\n", ptdev->profile_mask);
+}
+
+static ssize_t profiling_store(struct device *dev,
+			       struct device_attribute *attr,
+			       const char *buf, size_t len)
+{
+	struct panthor_device *ptdev = dev_get_drvdata(dev);
+	u32 value;
+	int err;
+
+	err = kstrtou32(buf, 0, &value);
+	if (err)
+		return err;
+
+	if ((value & ~PANTHOR_DEVICE_PROFILING_ALL) != 0)
+		return -EINVAL;
+
+	ptdev->profile_mask = value;
+
+	return len;
+}
+
+static DEVICE_ATTR_RW(profiling);
+
+static struct attribute *panthor_attrs[] = {
+	&dev_attr_profiling.attr,
+	NULL,
+};
+
+ATTRIBUTE_GROUPS(panthor);
+
 static const struct of_device_id dt_match[] = {
 	{ .compatible = "rockchip,rk3588-mali" },
 	{ .compatible = "arm,mali-valhall-csf" },
@@ -1555,6 +1593,7 @@ static struct platform_driver panthor_driver = {
 		.name = "panthor",
 		.pm = pm_ptr(&panthor_pm_ops),
 		.of_match_table = dt_match,
+		.dev_groups = panthor_groups,
 	},
 };