drm/modes: Parse overscan properties

Properly configuring the overscan properties might be needed for the
initial setup of the framebuffer for display that still have overscan.
Let's allow for more properties on the kernel command line to setup each
margin.
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/e481f1628e3768ca49226ec2115cfa4dfcbd5e4c.1560783090.git-series.maxime.ripard@bootlin.com

Documentation/fb/modedb.txt

@@ -57,6 +57,8 @@ Options can also be passed after the mode, using commas as separator.
 
 Valid options are:
 
+  - margin_top, margin_bottom, margin_left, margin_right (integer):
+    Number of pixels in the margins, typically to deal with overscan on TVs
   - reflect_x (boolean): Perform an axial symmetry on the X axis
   - reflect_y (boolean): Perform an axial symmetry on the Y axis
   - rotate (integer): Rotate the initial framebuffer by x

drivers/gpu/drm/drm_modes.c

@@ -1609,6 +1609,50 @@ static int drm_mode_parse_cmdline_options(char *str, size_t len,
 		} else if (!strncmp(option, "reflect_y", delim - option)) {
 			rotation |= DRM_MODE_REFLECT_Y;
 			sep = delim;
+		} else if (!strncmp(option, "margin_right", delim - option)) {
+			const char *value = delim + 1;
+			unsigned int margin;
+
+			margin = simple_strtol(value, &sep, 10);
+
+			/* Make sure we have parsed something */
+			if (sep == value)
+				return -EINVAL;
+
+			mode->tv_margins.right = margin;
+		} else if (!strncmp(option, "margin_left", delim - option)) {
+			const char *value = delim + 1;
+			unsigned int margin;
+
+			margin = simple_strtol(value, &sep, 10);
+
+			/* Make sure we have parsed something */
+			if (sep == value)
+				return -EINVAL;
+
+			mode->tv_margins.left = margin;
+		} else if (!strncmp(option, "margin_top", delim - option)) {
+			const char *value = delim + 1;
+			unsigned int margin;
+
+			margin = simple_strtol(value, &sep, 10);
+
+			/* Make sure we have parsed something */
+			if (sep == value)
+				return -EINVAL;
+
+			mode->tv_margins.top = margin;
+		} else if (!strncmp(option, "margin_bottom", delim - option)) {
+			const char *value = delim + 1;
+			unsigned int margin;
+
+			margin = simple_strtol(value, &sep, 10);
+
+			/* Make sure we have parsed something */
+			if (sep == value)
+				return -EINVAL;
+
+			mode->tv_margins.bottom = margin;
 		} else {
 			return -EINVAL;
 		}

include/drm/drm_connector.h

@@ -1054,6 +1054,11 @@ struct drm_cmdline_mode {
 	 * DRM_MODE_ROTATE_0 and DRM_MODE_ROTATE_180.
 	 */
 	unsigned int rotation_reflection;
+
+	/**
+	 * @tv_margins: TV margins to apply to the mode.
+	 */
+	struct drm_connector_tv_margins tv_margins;
 };
 
 /**