ACPI: video: Handle fetching EDID that is longer than 256 bytes

The ACPI specification allows for an EDID to be up to 512 bytes but
the _DDC EDID fetching code will only try up to 256 bytes.

Modify the code to instead start at 512 bytes and work it's way
down instead.

As _DDC is now called up to 4 times on a machine debugging messages
are noisier than necessary.  Decrease from info to debug.

Link: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/Apx_B_Video_Extensions/output-device-specific-methods.html#ddc-return-the-edid-for-this-device
Signed-off-by: Mario Limonciello <[email protected]>
[ rjw: Type mismatch fix, minor whitespace adjustment ]
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: superm1

drivers/acpi/acpi_video.c

@@ -612,7 +612,7 @@ acpi_video_device_lcd_get_level_current(struct acpi_video_device *device,
 
 static int
 acpi_video_device_EDID(struct acpi_video_device *device,
-		       union acpi_object **edid, ssize_t length)
+		       union acpi_object **edid, int length)
 {
 	int status;
 	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
@@ -625,13 +625,11 @@ acpi_video_device_EDID(struct acpi_video_device *device,
 
 	if (!device)
 		return -ENODEV;
-	if (length == 128)
-		arg0.integer.value = 1;
-	else if (length == 256)
-		arg0.integer.value = 2;
-	else
+	if (!length || (length % 128))
 		return -EINVAL;
 
+	arg0.integer.value = length / 128;
+
 	status = acpi_evaluate_object(device->dev->handle, "_DDC", &args, &buffer);
 	if (ACPI_FAILURE(status))
 		return -ENODEV;
@@ -641,7 +639,8 @@ acpi_video_device_EDID(struct acpi_video_device *device,
 	if (obj && obj->type == ACPI_TYPE_BUFFER)
 		*edid = obj;
 	else {
-		acpi_handle_info(device->dev->handle, "Invalid _DDC data\n");
+		acpi_handle_debug(device->dev->handle,
+				 "Invalid _DDC data for length %d\n", length);
 		status = -EFAULT;
 		kfree(obj);
 	}
@@ -1447,7 +1446,6 @@ int acpi_video_get_edid(struct acpi_device *device, int type, int device_id,
 
 	for (i = 0; i < video->attached_count; i++) {
 		video_device = video->attached_array[i].bind_info;
-		length = 256;
 
 		if (!video_device)
 			continue;
@@ -1478,18 +1476,14 @@ int acpi_video_get_edid(struct acpi_device *device, int type, int device_id,
 			continue;
 		}
 
-		status = acpi_video_device_EDID(video_device, &buffer, length);
-
-		if (ACPI_FAILURE(status) || !buffer ||
-		    buffer->type != ACPI_TYPE_BUFFER) {
-			length = 128;
+		for (length = 512; length > 0; length -= 128) {
 			status = acpi_video_device_EDID(video_device, &buffer,
 							length);
-			if (ACPI_FAILURE(status) || !buffer ||
-			    buffer->type != ACPI_TYPE_BUFFER) {
-				continue;
-			}
+			if (ACPI_SUCCESS(status))
+				break;
 		}
+		if (!length)
+			continue;
 
 		*edid = buffer->buffer.pointer;
 		return length;