drm/arcpgu: Opt in debugfs

This change adopts debugfs usage for outputting useful data.
As of today we print:
* Mode and real HW clock values
* Standard FB info

Code is heavily borrowed from ARM's HDLCD thus adding Liviu in Cc.

Signed-off-by: Alexey Brodkin <[e-mail]>
Reviewed-by: Liviu Dudau <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Jose Abreu <[e-mail]>

drivers/gpu/drm/arc/arcpgu_drv.c

···
 	return 0;
 }
 
+#ifdef CONFIG_DEBUG_FS
+static int arcpgu_show_pxlclock(struct seq_file *m, void *arg)
+{
+	struct drm_info_node *node = (struct drm_info_node *)m->private;
+	struct drm_device *drm = node->minor->dev;
+	struct arcpgu_drm_private *arcpgu = drm->dev_private;
+	unsigned long clkrate = clk_get_rate(arcpgu->clk);
+	unsigned long mode_clock = arcpgu->crtc.mode.crtc_clock * 1000;
+
+	seq_printf(m, "hw  : %lu\n", clkrate);
+	seq_printf(m, "mode: %lu\n", mode_clock);
+	return 0;
+}
+
+static struct drm_info_list arcpgu_debugfs_list[] = {
+	{ "clocks", arcpgu_show_pxlclock, 0 },
+	{ "fb", drm_fb_cma_debugfs_show, 0 },
+};
+
+static int arcpgu_debugfs_init(struct drm_minor *minor)
+{
+	return drm_debugfs_create_files(arcpgu_debugfs_list,
+		ARRAY_SIZE(arcpgu_debugfs_list), minor->debugfs_root, minor);
+}
+#endif
+
 static struct drm_driver arcpgu_drm_driver = {
 	.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_PRIME |
 			   DRIVER_ATOMIC,
···
 	.gem_prime_vmap = drm_gem_cma_prime_vmap,
 	.gem_prime_vunmap = drm_gem_cma_prime_vunmap,
 	.gem_prime_mmap = drm_gem_cma_prime_mmap,
+#ifdef CONFIG_DEBUG_FS
+	.debugfs_init = arcpgu_debugfs_init,
+#endif
 };
 
 static int arcpgu_probe(struct platform_device *pdev)