drm: Add common fdinfo helper

Handle a bit of the boiler-plate in a single case, and make it easier to
add some core tracked stats.  This also ensures consistent behavior
across drivers for standardised fields.

v2: Update drm-usage-stats.rst, 64b client-id, rename drm_show_fdinfo
v3: Rebase on drm-misc-next

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Acked-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230524155956.382440-3-robdclark@gmail.com

Documentation/gpu/drm-usage-stats.rst

@@ -126,7 +126,15 @@ percentage utilization of the engine, whereas drm-engine-<str> only reflects
 time active without considering what frequency the engine is operating as a
 percentage of it's maximum frequency.
 
+Implementation Details
+======================
+
+Drivers should use drm_show_fdinfo() in their `struct file_operations`, and
+implement &drm_driver.show_fdinfo if they wish to provide any stats which
+are not provided by drm_show_fdinfo().  But even driver specific stats should
+be documented above and where possible, aligned with other drivers.
+
 Driver specific implementations
-===============================
+-------------------------------
 
 :ref:`i915-usage-stats`

drivers/gpu/drm/drm_file.c

@@ -148,6 +148,7 @@ bool drm_dev_needs_global_mutex(struct drm_device *dev)
  */
 struct drm_file *drm_file_alloc(struct drm_minor *minor)
 {
+	static atomic64_t ident = ATOMIC_INIT(0);
 	struct drm_device *dev = minor->dev;
 	struct drm_file *file;
 	int ret;
@@ -156,6 +157,8 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor)
 	if (!file)
 		return ERR_PTR(-ENOMEM);
 
+	/* Get a unique identifier for fdinfo: */
+	file->client_id = atomic64_inc_return(&ident);
 	file->pid = get_pid(task_tgid(current));
 	file->minor = minor;
 
@@ -868,6 +871,38 @@ void drm_send_event(struct drm_device *dev, struct drm_pending_event *e)
 }
 EXPORT_SYMBOL(drm_send_event);
 
+/**
+ * drm_show_fdinfo - helper for drm file fops
+ * @seq_file: output stream
+ * @f: the device file instance
+ *
+ * Helper to implement fdinfo, for userspace to query usage stats, etc, of a
+ * process using the GPU.  See also &drm_driver.show_fdinfo.
+ *
+ * For text output format description please see Documentation/gpu/drm-usage-stats.rst
+ */
+void drm_show_fdinfo(struct seq_file *m, struct file *f)
+{
+	struct drm_file *file = f->private_data;
+	struct drm_device *dev = file->minor->dev;
+	struct drm_printer p = drm_seq_file_printer(m);
+
+	drm_printf(&p, "drm-driver:\t%s\n", dev->driver->name);
+	drm_printf(&p, "drm-client-id:\t%llu\n", file->client_id);
+
+	if (dev_is_pci(dev->dev)) {
+		struct pci_dev *pdev = to_pci_dev(dev->dev);
+
+		drm_printf(&p, "drm-pdev:\t%04x:%02x:%02x.%d\n",
+			   pci_domain_nr(pdev->bus), pdev->bus->number,
+			   PCI_SLOT(pdev->devfn), PCI_FUNC(pdev->devfn));
+	}
+
+	if (dev->driver->show_fdinfo)
+		dev->driver->show_fdinfo(&p, file);
+}
+EXPORT_SYMBOL(drm_show_fdinfo);
+
 /**
  * mock_drm_getfile - Create a new struct file for the drm device
  * @minor: drm minor to wrap (e.g. #drm_device.primary)

include/drm/drm_drv.h

@@ -401,6 +401,13 @@ struct drm_driver {
 			       struct drm_device *dev, uint32_t handle,
 			       uint64_t *offset);
 
+	/**
+	 * @show_fdinfo:
+	 *
+	 * Print device specific fdinfo.  See Documentation/gpu/drm-usage-stats.rst.
+	 */
+	void (*show_fdinfo)(struct drm_printer *p, struct drm_file *f);
+
 	/** @major: driver major number */
 	int major;
 	/** @minor: driver minor number */

include/drm/drm_file.h

@@ -258,6 +258,9 @@ struct drm_file {
 	/** @pid: Process that opened this file. */
 	struct pid *pid;
 
+	/** @client_id: A unique id for fdinfo */
+	u64 client_id;
+
 	/** @magic: Authentication magic, see @authenticated. */
 	drm_magic_t magic;
 
@@ -438,6 +441,7 @@ void drm_send_event(struct drm_device *dev, struct drm_pending_event *e);
 void drm_send_event_timestamp_locked(struct drm_device *dev,
 				     struct drm_pending_event *e,
 				     ktime_t timestamp);
+void drm_show_fdinfo(struct seq_file *m, struct file *f);
 
 struct file *mock_drm_getfile(struct drm_minor *minor, unsigned int flags);