Commit 5d389afc authored by Mario Limonciello's avatar Mario Limonciello Committed by Rafael J. Wysocki
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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: default avatarMario Limonciello <mario.limonciello@amd.com>
[ rjw: Type mismatch fix, minor whitespace adjustment ]
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 54be6c6c

drivers/acpi/acpi_video.c

+11 −17
Original line number Diff line number Diff line
@@ -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;