drm: Add DRM_MODE_TV_MODE_MONOCHROME

Add this as a value for enum_drm_connector_tv_mode, represented
by the string "Mono", to generate video with no colour encoding
or bursts. Define it to have no pedestal (since only NTSC-M calls
for a pedestal).

Change default mode creation to acommodate the new tv_mode value
which comprises both 525-line and 625-line formats.
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240216184857.245372-2-dave.stevenson@raspberrypi.com

drivers/gpu/drm/drm_connector.c

@@ -1087,6 +1087,7 @@ static const struct drm_prop_enum_list drm_tv_mode_enum_list[] = {
 	{ DRM_MODE_TV_MODE_PAL_M, "PAL-M" },
 	{ DRM_MODE_TV_MODE_PAL_N, "PAL-N" },
 	{ DRM_MODE_TV_MODE_SECAM, "SECAM" },
+	{ DRM_MODE_TV_MODE_MONOCHROME, "Mono" },
 };
 DRM_ENUM_NAME_FN(drm_get_tv_mode_name, drm_tv_mode_enum_list)
 
@@ -1858,6 +1859,12 @@ EXPORT_SYMBOL(drm_connector_attach_dp_subconnector_property);
  *		TV Mode is CCIR System B (aka 625-lines) together with
  *		the SECAM Color Encoding.
  *
+ *	Mono:
+ *
+ *		Use timings appropriate to the DRM mode, including
+ *		equalizing pulses for a 525-line or 625-line mode,
+ *		with no pedestal or color encoding.
+ *
  *	Drivers can set up this property by calling
  *	drm_mode_create_tv_properties().
  */

drivers/gpu/drm/drm_modes.c

@@ -531,7 +531,8 @@ static int fill_analog_mode(struct drm_device *dev,
  * @interlace: whether to compute an interlaced mode
  *
  * This function creates a struct drm_display_mode instance suited for
- * an analog TV output, for one of the usual analog TV mode.
+ * an analog TV output, for one of the usual analog TV modes. Where
+ * this is DRM_MODE_TV_MODE_MONOCHROME, a 625-line mode will be created.
  *
  * Note that @hdisplay is larger than the usual constraints for the PAL
  * and NTSC timings, and we'll choose to ignore most timings constraints
@@ -569,6 +570,8 @@ struct drm_display_mode *drm_analog_tv_mode(struct drm_device *dev,
 	case DRM_MODE_TV_MODE_PAL_N:
 		fallthrough;
 	case DRM_MODE_TV_MODE_SECAM:
+		fallthrough;
+	case DRM_MODE_TV_MODE_MONOCHROME:
 		analog = DRM_MODE_ANALOG_PAL;
 		break;
 

drivers/gpu/drm/drm_probe_helper.c

@@ -1259,8 +1259,9 @@ int drm_connector_helper_tv_get_modes(struct drm_connector *connector)
 	for (i = 0; i < tv_mode_property->num_values; i++)
 		supported_tv_modes |= BIT(tv_mode_property->values[i]);
 
-	if ((supported_tv_modes & ntsc_modes) &&
-	    (supported_tv_modes & pal_modes)) {
+	if (((supported_tv_modes & ntsc_modes) &&
+	     (supported_tv_modes & pal_modes)) ||
+	    (supported_tv_modes & BIT(DRM_MODE_TV_MODE_MONOCHROME))) {
 		uint64_t default_mode;
 
 		if (drm_object_property_get_default_value(&connector->base,

include/drm/drm_connector.h

@@ -201,6 +201,13 @@ enum drm_connector_tv_mode {
 	 */
 	DRM_MODE_TV_MODE_SECAM,
 
+	/**
+	 * @DRM_MODE_TV_MODE_MONOCHROME: Use timings appropriate to
+	 * the DRM mode, including equalizing pulses for a 525-line
+	 * or 625-line mode, with no pedestal or color encoding.
+	 */
+	DRM_MODE_TV_MODE_MONOCHROME,
+
 	/**
 	 * @DRM_MODE_TV_MODE_MAX: Number of analog TV output modes.
 	 *