drm/i915/display/debug: Expose crtc current bpc via debugfs

This new debugfs will expose the currently using bpc by crtc.
It is very useful for verifying whether we enter the correct
output color depth from IGT.

This patch will also add the connector's max supported bpc to
"i915_display_info" debugfs.

Example:
cat /sys/kernel/debug/dri/0/crtc-0/i915_current_bpc
Current: 8

Cc: Jani Nikula <[e-mail]>
Cc: Ville Syrjälä <[e-mail]>
Cc: Uma Shankar <[e-mail]>
Signed-off-by: Bhanuprakash Modem <[e-mail]>
Reviewed-by: Arun R Murthy <[e-mail]>
Acked-by: Jani Nikula <[e-mail]>
Signed-off-by: Jani Nikula <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/i915/display/intel_display_debugfs.c

···
 	seq_puts(m, "\tHDCP version: ");
 	intel_hdcp_info(m, intel_connector);
 
+	seq_printf(m, "\tmax bpc: %u\n", connector->display_info.bpc);
+
 	intel_panel_info(m, intel_connector);
 
 	seq_printf(m, "\tmodes:\n");
···
 	.write = i915_dsc_bpp_write
 };
 
+/*
+ * Returns the Current CRTC's bpc.
+ * Example usage: cat /sys/kernel/debug/dri/0/crtc-0/i915_current_bpc
+ */
+static int i915_current_bpc_show(struct seq_file *m, void *data)
+{
+	struct intel_crtc *crtc = to_intel_crtc(m->private);
+	struct intel_crtc_state *crtc_state;
+	int ret;
+
+	ret = drm_modeset_lock_single_interruptible(&crtc->base.mutex);
+	if (ret)
+		return ret;
+
+	crtc_state = to_intel_crtc_state(crtc->base.state);
+	seq_printf(m, "Current: %u\n", crtc_state->pipe_bpp / 3);
+
+	drm_modeset_unlock(&crtc->base.mutex);
+
+	return ret;
+}
+DEFINE_SHOW_ATTRIBUTE(i915_current_bpc);
+
 /**
  * intel_connector_debugfs_add - add i915 specific connector debugfs files
  * @connector: pointer to a registered drm_connector
···
 
 	crtc_updates_add(crtc);
 	intel_fbc_crtc_debugfs_add(to_intel_crtc(crtc));
+
+	debugfs_create_file("i915_current_bpc", 0444, crtc->debugfs_entry, crtc,
+			    &i915_current_bpc_fops);
 }