[PATCH] drm/i915/display/debugfs: Add connector debugfs for "output_bpc"

[Bhanuprakash Modem]

This new debugfs will expose the connector's max supported bpc
and the bpc currently using. It is very useful for verifying
whether we enter the correct output color depth from IGT.

Example:
cat /sys/kernel/debug/dri/0/DP-1/output_bpc
Current: 8
Maximum: 10

Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Uma Shankar <uma.shankar at intel.com>
Cc: Swati Sharma <swati2.sharma at intel.com>
Signed-off-by: Bhanuprakash Modem <bhanuprakash.modem at intel.com>
---
 .../drm/i915/display/intel_display_debugfs.c  | 44 +++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display_debugfs.c b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
index c1e74a13a0828..ea2118eac0ea8 100644
--- a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
+++ b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
@@ -2275,6 +2275,47 @@ static const struct file_operations i915_dsc_bpp_fops = {
 	.write = i915_dsc_bpp_write
 };
 
+/*
+ * Returns the maximum output bpc for the connector.
+ * Example usage: cat /sys/kernel/debug/dri/0/DP-1/output_bpc
+ */
+static int output_bpc_show(struct seq_file *m, void *data)
+{
+	struct drm_connector *connector = m->private;
+	struct drm_device *dev = connector->dev;
+	struct drm_crtc *crtc;
+	struct intel_crtc_state *crtc_state;
+	struct intel_encoder *encoder = intel_attached_encoder(to_intel_connector(connector));
+	int res;
+
+	if (!encoder)
+		return -ENODEV;
+
+	res = drm_modeset_lock_single_interruptible(&dev->mode_config.connection_mutex);
+	if (res)
+		return res;
+
+	crtc = connector->state->crtc;
+	if (connector->status != connector_status_connected || !crtc) {
+		res = -ENODEV;
+		goto unlock;
+	}
+
+	crtc_state = to_intel_crtc_state(crtc->state);
+	if (!crtc_state->hw.active)
+		goto unlock;
+
+	seq_printf(m, "Current: %u\n", crtc_state->pipe_bpp / 3);
+	seq_printf(m, "Maximum: %u\n", connector->display_info.bpc);
+	res = 0;
+
+unlock:
+	drm_modeset_unlock(&dev->mode_config.connection_mutex);
+
+	return res;
+}
+DEFINE_SHOW_ATTRIBUTE(output_bpc);
+
 /**
  * intel_connector_debugfs_add - add i915 specific connector debugfs files
  * @connector: pointer to a registered drm_connector
@@ -2330,6 +2371,9 @@ void intel_connector_debugfs_add(struct intel_connector *intel_connector)
 	    connector->connector_type == DRM_MODE_CONNECTOR_HDMIB)
 		debugfs_create_file("i915_lpsp_capability", 0444, root,
 				    connector, &i915_lpsp_capability_fops);
+
+	debugfs_create_file("output_bpc", S_IRUGO, root,
+			    connector, &output_bpc_fops);
 }
 
 /**
-- 
2.35.1