drm/simpledrm: Allow physical width and height configuration via panel node

Parse the width-mm and height-mm devicetree properties of the panel node,
and use this to set the DRM Display Mode instead of calculating it
based on a hardcoded DPI.
Signed-off-by: Rayyan Ansari <rayyan@ansari.sh>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230126182435.70544-2-rayyan@ansari.sh

drivers/gpu/drm/tiny/simpledrm.c

@@ -606,16 +606,12 @@ static const struct drm_mode_config_funcs simpledrm_mode_config_funcs = {
  */
 
 static struct drm_display_mode simpledrm_mode(unsigned int width,
-					      unsigned int height)
+					      unsigned int height,
+					      unsigned int width_mm,
+					      unsigned int height_mm)
 {
-	/*
-	 * Assume a monitor resolution of 96 dpi to
-	 * get a somewhat reasonable screen size.
-	 */
 	const struct drm_display_mode mode = {
-		DRM_MODE_INIT(60, width, height,
-			      DRM_MODE_RES_MM(width, 96ul),
-			      DRM_MODE_RES_MM(height, 96ul))
+		DRM_MODE_INIT(60, width, height, width_mm, height_mm)
 	};
 
 	return mode;
@@ -629,6 +625,8 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
 	struct simpledrm_device *sdev;
 	struct drm_device *dev;
 	int width, height, stride;
+	int width_mm = 0, height_mm = 0;
+	struct device_node *panel_node;
 	const struct drm_format_info *format;
 	struct resource *res, *mem = NULL;
 	struct drm_plane *primary_plane;
@@ -685,6 +683,12 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
 		mem = simplefb_get_memory_of(dev, of_node);
 		if (IS_ERR(mem))
 			return ERR_CAST(mem);
+		panel_node = of_parse_phandle(of_node, "panel", 0);
+		if (panel_node) {
+			simplefb_read_u32_of(dev, panel_node, "width-mm", &width_mm);
+			simplefb_read_u32_of(dev, panel_node, "height-mm", &height_mm);
+			of_node_put(panel_node);
+		}
 	} else {
 		drm_err(dev, "no simplefb configuration found\n");
 		return ERR_PTR(-ENODEV);
@@ -695,7 +699,16 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
 			return ERR_PTR(-EINVAL);
 	}
 
-	sdev->mode = simpledrm_mode(width, height);
+	/*
+	 * Assume a monitor resolution of 96 dpi if physical dimensions
+	 * are not specified to get a somewhat reasonable screen size.
+	 */
+	if (!width_mm)
+		width_mm = DRM_MODE_RES_MM(width, 96ul);
+	if (!height_mm)
+		height_mm = DRM_MODE_RES_MM(height, 96ul);
+
+	sdev->mode = simpledrm_mode(width, height, width_mm, height_mm);
 	sdev->format = format;
 	sdev->pitch = stride;