drm/ast: astdp: Use struct drm_edid and helpers

Convert ASTDP support to struct drm_edid and its helpers. Simplifies
and modernizes the EDID handling.

The driver reads 4 bytes at once, but the overall read length is now
variable. Therefore update the EDID read loop to never return more than
the requested bytes.

The device does not seem to support EDID extensions, as the driver
actively clears any such information from the main EDID header. As
the new interface allows for reading extension blocks for EDID, make
sure that the block is always 0 (i.e., the main header). A later
update might fix that.

v2:
- fix reading if len is not a multiple of 4
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240815151953.184679-5-tzimmermann@suse.de

drivers/gpu/drm/ast/ast_dp.c

@@ -20,11 +20,15 @@ static bool ast_astdp_is_connected(struct ast_device *ast)
 	return true;
 }
 
-static int ast_astdp_read_edid(struct drm_device *dev, u8 *ediddata)
+static int ast_astdp_read_edid_block(void *data, u8 *buf, unsigned int block, size_t len)
 {
-	struct ast_device *ast = to_ast_device(dev);
+	struct ast_device *ast = data;
+	size_t rdlen = round_up(len, 4);
 	int ret = 0;
-	u8 i;
+	unsigned int i;
+
+	if (block > 0)
+		return -EIO; /* extension headers not supported */
 
 	/*
 	 * Protect access to I/O registers from concurrent modesetting
@@ -35,13 +39,23 @@ static int ast_astdp_read_edid(struct drm_device *dev, u8 *ediddata)
 	/* Start reading EDID data */
 	ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0xe5, (u8)~AST_IO_VGACRE5_EDID_READ_DONE, 0x00);
 
-	for (i = 0; i < 32; i++) {
+	for (i = 0; i < rdlen; i += 4) {
+		unsigned int offset;
 		unsigned int j;
+		u8 ediddata[4];
+		u8 vgacre4;
+
+		offset = (i + block * EDID_LENGTH) / 4;
+		if (offset >= 64) {
+			ret = -EIO;
+			goto out;
+		}
+		vgacre4 = offset;
 
 		/*
 		 * CRE4[7:0]: Read-Pointer for EDID (Unit: 4bytes); valid range: 0~64
 		 */
-		ast_set_index_reg(ast, AST_IO_VGACRI, 0xe4, i);
+		ast_set_index_reg(ast, AST_IO_VGACRI, 0xe4, vgacre4);
 
 		/*
 		 * CRD7[b0]: valid flag for EDID
@@ -65,7 +79,7 @@ static int ast_astdp_read_edid(struct drm_device *dev, u8 *ediddata)
 			vgacrd7 = ast_get_index_reg(ast, AST_IO_VGACRI, 0xd7);
 			if (vgacrd7 & AST_IO_VGACRD7_EDID_VALID_FLAG) {
 				vgacrd6 = ast_get_index_reg(ast, AST_IO_VGACRI, 0xd6);
-				if (vgacrd6 == i)
+				if (vgacrd6 == offset)
 					break;
 			}
 		}
@@ -93,7 +107,8 @@ static int ast_astdp_read_edid(struct drm_device *dev, u8 *ediddata)
 			ediddata[2] = 0;
 		}
 
-		ediddata += 4;
+		memcpy(buf, ediddata, min((len - i), 4));
+		buf += 4;
 	}
 
 out:
@@ -331,29 +346,17 @@ static const struct drm_encoder_helper_funcs ast_astdp_encoder_helper_funcs = {
 
 static int ast_astdp_connector_helper_get_modes(struct drm_connector *connector)
 {
-	void *edid;
-	int succ;
+	struct drm_device *dev = connector->dev;
+	struct ast_device *ast = to_ast_device(dev);
+	const struct drm_edid *drm_edid;
 	int count;
 
-	edid = kmalloc(EDID_LENGTH, GFP_KERNEL);
-	if (!edid)
-		goto err_drm_connector_update_edid_property;
-
-	succ = ast_astdp_read_edid(connector->dev, edid);
-	if (succ < 0)
-		goto err_kfree;
-
-	drm_connector_update_edid_property(connector, edid);
-	count = drm_add_edid_modes(connector, edid);
-	kfree(edid);
+	drm_edid = drm_edid_read_custom(connector, ast_astdp_read_edid_block, ast);
+	drm_edid_connector_update(connector, drm_edid);
+	count = drm_edid_connector_add_modes(connector);
+	drm_edid_free(drm_edid);
 
 	return count;
-
-err_kfree:
-	kfree(edid);
-err_drm_connector_update_edid_property:
-	drm_connector_update_edid_property(connector, NULL);
-	return 0;
 }
 
 static int ast_astdp_connector_helper_detect_ctx(struct drm_connector *connector,