drm/i915: Add bigjoiner force enable option to debugfs

For validation purposes, it might be useful to be able to
force Bigjoiner mode, even if current dotclock/resolution
do not require that.
Lets add such to option to debugfs.

v2: - Apparently intel_dp_need_bigjoiner can't be used, when
      debugfs entry is created so lets just check manually
      the DISPLAY_VER.

v3: - Switch to intel_connector from drm_connector(Jani Nikula)
    - Remove redundant modeset lock(Jani Nikula)
    - Use kstrtobool_from_user for boolean value(Jani Nikula)

v4: - Apply the changes to proper function(Jani Nikula)

v5: - Removed unnecessary check from i915_bigjoiner_enable_show
      (Ville Syrjälä)
    - Added eDP connector check to intel_connector_debugfs_add
      (Ville Syrjälä)
    - Removed debug message in order to prevent dmesg flooding
      (Ville Syrjälä)

v6: - Assume now always that m->private is intel_connector
    - Fixed other similar conflicts

v7: - Move bigjoiner force option to intel_connector(Ville Syrjälä)
    - Use DEFINE_SHOW_STORE_ATTRIBUTE instead of defining fops
      manually.(Ville Syrjälä)

v8: - Pass intel_connector to debugfs_create_file, instead of drm_connector.
      (Jani Nikula)
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240212125011.66174-1-uma.shankar@intel.com

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

@@ -1391,6 +1391,20 @@ out:	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
 	return ret;
 }
 
+static int i915_bigjoiner_enable_show(struct seq_file *m, void *data)
+{
+	struct intel_connector *connector = m->private;
+	struct drm_crtc *crtc;
+
+	crtc = connector->base.state->crtc;
+	if (connector->base.status != connector_status_connected || !crtc)
+		return -ENODEV;
+
+	seq_printf(m, "Bigjoiner enable: %d\n", connector->force_bigjoiner_enable);
+
+	return 0;
+}
+
 static ssize_t i915_dsc_output_format_write(struct file *file,
 					    const char __user *ubuf,
 					    size_t len, loff_t *offp)
@@ -1412,6 +1426,30 @@ static ssize_t i915_dsc_output_format_write(struct file *file,
 	return len;
 }
 
+static ssize_t i915_bigjoiner_enable_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 drm_crtc *crtc;
+	bool bigjoiner_en = 0;
+	int ret;
+
+	crtc = connector->base.state->crtc;
+	if (connector->base.status != connector_status_connected || !crtc)
+		return -ENODEV;
+
+	ret = kstrtobool_from_user(ubuf, len, &bigjoiner_en);
+	if (ret < 0)
+		return ret;
+
+	connector->force_bigjoiner_enable = bigjoiner_en;
+	*offp += len;
+
+	return len;
+}
+
 static int i915_dsc_output_format_open(struct inode *inode,
 				       struct file *file)
 {
@@ -1505,6 +1543,8 @@ static const struct file_operations i915_dsc_fractional_bpp_fops = {
 	.write = i915_dsc_fractional_bpp_write
 };
 
+DEFINE_SHOW_STORE_ATTRIBUTE(i915_bigjoiner_enable);
+
 /*
  * Returns the Current CRTC's bpc.
  * Example usage: cat /sys/kernel/debug/dri/0/crtc-0/i915_current_bpc
@@ -1586,6 +1626,13 @@ void intel_connector_debugfs_add(struct intel_connector *connector)
 				    connector, &i915_dsc_fractional_bpp_fops);
 	}
 
+	if (DISPLAY_VER(i915) >= 11 &&
+	    (connector_type == DRM_MODE_CONNECTOR_DisplayPort ||
+	     connector_type == DRM_MODE_CONNECTOR_eDP)) {
+		debugfs_create_file("i915_bigjoiner_force_enable", 0644, root,
+				    connector, &i915_bigjoiner_enable_fops);
+	}
+
 	if (connector_type == DRM_MODE_CONNECTOR_DSI ||
 	    connector_type == DRM_MODE_CONNECTOR_eDP ||
 	    connector_type == DRM_MODE_CONNECTOR_DisplayPort ||

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

@@ -626,6 +626,8 @@ struct intel_connector {
 
 	struct intel_dp *mst_port;
 
+	bool force_bigjoiner_enable;
+
 	struct {
 		struct drm_dp_aux *dsc_decompression_aux;
 		u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE];

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

@@ -1205,11 +1205,13 @@ bool intel_dp_need_bigjoiner(struct intel_dp *intel_dp,
 			     int hdisplay, int clock)
 {
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+	struct intel_connector *connector = intel_dp->attached_connector;
 
 	if (!intel_dp_can_bigjoiner(intel_dp))
 		return false;
 
-	return clock > i915->max_dotclk_freq || hdisplay > 5120;
+	return clock > i915->max_dotclk_freq || hdisplay > 5120 ||
+	       connector->force_bigjoiner_enable;
 }
 
 static enum drm_mode_status