[PATCH v4 1/2] drm/simpledrm: Allow physical width and height configuration via panel node

[Rayyan Ansari <rayyan@ansari.sh>]

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>
---
 drivers/gpu/drm/tiny/simpledrm.c | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/tiny/simpledrm.c b/drivers/gpu/drm/tiny/simpledrm.c
index 162eb44dcba8..f8b18441cfcb 100644
--- a/drivers/gpu/drm/tiny/simpledrm.c
+++ b/drivers/gpu/drm/tiny/simpledrm.c
@@ -599,16 +599,12 @@ 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;
@@ -622,6 +618,8 @@ 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;
 	void __iomem *screen_base;
@@ -676,6 +674,13 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
 		format = simplefb_get_format_of(dev, of_node);
 		if (IS_ERR(format))
 			return ERR_CAST(format);
+
+		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);
@@ -686,7 +691,16 @@ 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;
 
-- 
2.39.1