drm/i915/hdcp: Create force_hdcp14 debug fs entry

Testing HDCP 1.4 becomes tough since the only way our code comes to
HDCP 1.4 pathway is if the monitor only supports HDCP 1.4 which
becomes tough to find sometimes.
Setting this debug_fs entry will force use to use the HDCP 1.4 path
so that more robust HDCP 1.4 testing can take place.

--v2
-Move the code to intel_hdcp.c [Jani]
-Remove useless debug logging [Jani]
-Remove Force_HDCP from the debug file [Jani]

--v3
-Remove leftover debug loggings [Jani]

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250213082541.3772212-1-suraj.kandpal@intel.com

Author: surajk8

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -496,6 +496,8 @@ struct intel_hdcp {
 	enum transcoder cpu_transcoder;
 	/* Only used for DP MST stream encryption */
 	enum transcoder stream_transcoder;
+	/* Used to force HDCP 1.4 bypassing HDCP 2.x */
+	bool force_hdcp14;
 };
 
 struct intel_connector {

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

@@ -2472,13 +2472,16 @@ static int _intel_hdcp_enable(struct intel_atomic_state *state,
 	 * Considering that HDCP2.2 is more secure than HDCP1.4, If the setup
 	 * is capable of HDCP2.2, it is preferred to use HDCP2.2.
 	 */
-	if (intel_hdcp2_get_capability(connector)) {
+	if (!hdcp->force_hdcp14 && intel_hdcp2_get_capability(connector)) {
 		ret = _intel_hdcp2_enable(state, connector);
 		if (!ret)
 			check_link_interval =
 				DRM_HDCP2_CHECK_PERIOD_MS;
 	}
 
+	if (hdcp->force_hdcp14)
+		drm_dbg_kms(display->drm, "Forcing HDCP 1.4\n");
+
 	/*
 	 * When HDCP2.2 fails and Content Type is not Type1, HDCP1.4 will
 	 * be attempted.
@@ -2806,6 +2809,75 @@ static int intel_hdcp_sink_capability_show(struct seq_file *m, void *data)
 }
 DEFINE_SHOW_ATTRIBUTE(intel_hdcp_sink_capability);
 
+static ssize_t intel_hdcp_force_14_write(struct file *file,
+					 const char __user *ubuf,
+					 size_t len, loff_t *offp)
+{
+	struct seq_file *m = file->private_data;
+	struct intel_connector *connector = m->private;
+	struct intel_hdcp *hdcp = &connector->hdcp;
+	bool force_hdcp14 = false;
+	int ret;
+
+	if (len == 0)
+		return 0;
+
+	ret = kstrtobool_from_user(ubuf, len, &force_hdcp14);
+	if (ret < 0)
+		return ret;
+
+	hdcp->force_hdcp14 = force_hdcp14;
+	*offp += len;
+
+	return len;
+}
+
+static int intel_hdcp_force_14_show(struct seq_file *m, void *data)
+{
+	struct intel_connector *connector = m->private;
+	struct intel_display *display = to_intel_display(connector);
+	struct intel_encoder *encoder = intel_attached_encoder(connector);
+	struct intel_hdcp *hdcp = &connector->hdcp;
+	struct drm_crtc *crtc;
+	int ret;
+
+	if (!encoder)
+		return -ENODEV;
+
+	ret = drm_modeset_lock_single_interruptible(&display->drm->mode_config.connection_mutex);
+	if (ret)
+		return ret;
+
+	crtc = connector->base.state->crtc;
+	if (connector->base.status != connector_status_connected || !crtc) {
+		ret = -ENODEV;
+		goto out;
+	}
+
+	seq_printf(m, "%s\n",
+		   str_yes_no(hdcp->force_hdcp14));
+out:
+	drm_modeset_unlock(&display->drm->mode_config.connection_mutex);
+
+	return ret;
+}
+
+static int intel_hdcp_force_14_open(struct inode *inode,
+				    struct file *file)
+{
+	return single_open(file, intel_hdcp_force_14_show,
+			   inode->i_private);
+}
+
+static const struct file_operations intel_hdcp_force_14_fops = {
+	.owner = THIS_MODULE,
+	.open = intel_hdcp_force_14_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+	.write = intel_hdcp_force_14_write
+};
+
 void intel_hdcp_connector_debugfs_add(struct intel_connector *connector)
 {
 	struct dentry *root = connector->base.debugfs_entry;
@@ -2816,5 +2888,7 @@ void intel_hdcp_connector_debugfs_add(struct intel_connector *connector)
 	    connector_type == DRM_MODE_CONNECTOR_HDMIB) {
 		debugfs_create_file("i915_hdcp_sink_capability", 0444, root,
 				    connector, &intel_hdcp_sink_capability_fops);
+		debugfs_create_file("i915_force_hdcp14", 0644, root,
+				    connector, &intel_hdcp_force_14_fops);
 	}
 }