drm/v3d: Create new IOCTL to expose performance counters information

Userspace usually needs some information about the performance counters
available. Although we could replicate this information in the kernel
and user-space, let's use the kernel as the "single source of truth" to
avoid issues in the future (e.g. list of performance counters is updated
in user-space, but not in the kernel, generating invalid requests).

Therefore, create a new IOCTL to expose the performance counters
information, that is name, category, and description.
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240512222655.2792754-5-mcanal@igalia.com

drivers/gpu/drm/v3d/v3d_drv.c

@@ -211,6 +211,7 @@ static const struct drm_ioctl_desc v3d_drm_ioctls[] = {
 	DRM_IOCTL_DEF_DRV(V3D_PERFMON_DESTROY, v3d_perfmon_destroy_ioctl, DRM_RENDER_ALLOW),
 	DRM_IOCTL_DEF_DRV(V3D_PERFMON_GET_VALUES, v3d_perfmon_get_values_ioctl, DRM_RENDER_ALLOW),
 	DRM_IOCTL_DEF_DRV(V3D_SUBMIT_CPU, v3d_submit_cpu_ioctl, DRM_RENDER_ALLOW | DRM_AUTH),
+	DRM_IOCTL_DEF_DRV(V3D_PERFMON_GET_COUNTER, v3d_perfmon_get_counter_ioctl, DRM_RENDER_ALLOW),
 };
 
 static const struct drm_driver v3d_drm_driver = {

drivers/gpu/drm/v3d/v3d_drv.h

@@ -582,6 +582,8 @@ int v3d_perfmon_destroy_ioctl(struct drm_device *dev, void *data,
 			      struct drm_file *file_priv);
 int v3d_perfmon_get_values_ioctl(struct drm_device *dev, void *data,
 				 struct drm_file *file_priv);
+int v3d_perfmon_get_counter_ioctl(struct drm_device *dev, void *data,
+				  struct drm_file *file_priv);
 
 /* v3d_sysfs.c */
 int v3d_sysfs_init(struct device *dev);

drivers/gpu/drm/v3d/v3d_perfmon.c

@@ -217,3 +217,36 @@ int v3d_perfmon_get_values_ioctl(struct drm_device *dev, void *data,
 
 	return ret;
 }
+
+int v3d_perfmon_get_counter_ioctl(struct drm_device *dev, void *data,
+				  struct drm_file *file_priv)
+{
+	struct drm_v3d_perfmon_get_counter *req = data;
+	struct v3d_dev *v3d = to_v3d_dev(dev);
+	const struct v3d_perf_counter_desc *counter;
+
+	for (int i = 0; i < ARRAY_SIZE(req->reserved); i++) {
+		if (req->reserved[i] != 0)
+			return -EINVAL;
+	}
+
+	/* Make sure that the counter ID is valid */
+	if (req->counter >= v3d->max_counters)
+		return -EINVAL;
+
+	if (v3d->ver >= 71) {
+		WARN_ON(v3d->max_counters != ARRAY_SIZE(v3d_v71_performance_counters));
+		counter = &v3d_v71_performance_counters[req->counter];
+	} else if (v3d->ver >= 42) {
+		WARN_ON(v3d->max_counters != ARRAY_SIZE(v3d_v42_performance_counters));
+		counter = &v3d_v42_performance_counters[req->counter];
+	} else {
+		return -EOPNOTSUPP;
+	}
+
+	strscpy(req->name, counter->name, sizeof(req->name));
+	strscpy(req->category, counter->category, sizeof(req->category));
+	strscpy(req->description, counter->description, sizeof(req->description));
+
+	return 0;
+}

include/uapi/drm/v3d_drm.h

@@ -42,6 +42,7 @@ extern "C" {
 #define DRM_V3D_PERFMON_DESTROY                   0x09
 #define DRM_V3D_PERFMON_GET_VALUES                0x0a
 #define DRM_V3D_SUBMIT_CPU                        0x0b
+#define DRM_V3D_PERFMON_GET_COUNTER               0x0c
 
 #define DRM_IOCTL_V3D_SUBMIT_CL           DRM_IOWR(DRM_COMMAND_BASE + DRM_V3D_SUBMIT_CL, struct drm_v3d_submit_cl)
 #define DRM_IOCTL_V3D_WAIT_BO             DRM_IOWR(DRM_COMMAND_BASE + DRM_V3D_WAIT_BO, struct drm_v3d_wait_bo)
@@ -58,6 +59,8 @@ extern "C" {
 #define DRM_IOCTL_V3D_PERFMON_GET_VALUES  DRM_IOWR(DRM_COMMAND_BASE + DRM_V3D_PERFMON_GET_VALUES, \
 						   struct drm_v3d_perfmon_get_values)
 #define DRM_IOCTL_V3D_SUBMIT_CPU          DRM_IOW(DRM_COMMAND_BASE + DRM_V3D_SUBMIT_CPU, struct drm_v3d_submit_cpu)
+#define DRM_IOCTL_V3D_PERFMON_GET_COUNTER DRM_IOWR(DRM_COMMAND_BASE + DRM_V3D_PERFMON_GET_COUNTER, \
+						   struct drm_v3d_perfmon_get_counter)
 
 #define DRM_V3D_SUBMIT_CL_FLUSH_CACHE             0x01
 #define DRM_V3D_SUBMIT_EXTENSION		  0x02
@@ -718,6 +721,40 @@ struct drm_v3d_perfmon_get_values {
 	__u64 values_ptr;
 };
 
+#define DRM_V3D_PERFCNT_MAX_NAME 64
+#define DRM_V3D_PERFCNT_MAX_CATEGORY 32
+#define DRM_V3D_PERFCNT_MAX_DESCRIPTION 256
+
+/**
+ * struct drm_v3d_perfmon_get_counter - ioctl to get the description of a
+ * performance counter
+ *
+ * As userspace needs to retrieve information about the performance counters
+ * available, this IOCTL allows users to get information about a performance
+ * counter (name, category and description).
+ */
+struct drm_v3d_perfmon_get_counter {
+	/*
+	 * Counter ID
+	 *
+	 * Must be smaller than the maximum number of performance counters, which
+	 * can be retrieve through DRM_V3D_PARAM_MAX_PERF_COUNTERS.
+	 */
+	__u8 counter;
+
+	/* Name of the counter */
+	__u8 name[DRM_V3D_PERFCNT_MAX_NAME];
+
+	/* Category of the counter */
+	__u8 category[DRM_V3D_PERFCNT_MAX_CATEGORY];
+
+	/* Description of the counter */
+	__u8 description[DRM_V3D_PERFCNT_MAX_DESCRIPTION];
+
+	/* mbz */
+	__u8 reserved[7];
+};
+
 #if defined(__cplusplus)
 }
 #endif