8.27. ioctl VIDIOC_G_EDID, VIDIOC_S_EDID, VIDIOC_SUBDEV_G_EDID, VIDIOC_SUBDEV_S_EDID

8.27.1. Name

VIDIOC_G_EDID - VIDIOC_S_EDID - VIDIOC_SUBDEV_G_EDID - VIDIOC_SUBDEV_S_EDID - Get or set the EDID of a video receiver/transmitter

8.27.2. Synopsis

int ioctl(int fd, VIDIOC_G_EDID, struct v4l2_edid *argp)

int ioctl(int fd, VIDIOC_S_EDID, struct v4l2_edid *argp)

int ioctl(int fd, VIDIOC_SUBDEV_G_EDID, struct v4l2_edid *argp)

int ioctl(int fd, VIDIOC_SUBDEV_S_EDID, struct v4l2_edid *argp)

8.27.3. Arguments

fd

File descriptor returned by open().

argp

8.27.4. Description

These ioctls can be used to get or set an EDID associated with an input from a receiver or an output of a transmitter device. They can be used with subdevice nodes (/dev/v4l-subdevX) or with video nodes (/dev/videoX).

When used with video nodes the pad field represents the input (for video capture devices) or output (for video output devices) index as is returned by ioctl VIDIOC_ENUMINPUT and ioctl VIDIOC_ENUMOUTPUT respectively. When used with subdevice nodes the pad field represents the input or output pad of the subdevice. If there is no EDID support for the given pad value, then the EINVAL error code will be returned.

To get the EDID data the application has to fill in the pad, start_block, blocks and edid fields, zero the reserved array and call VIDIOC_G_EDID. The current EDID from block start_block and of size blocks will be placed in the memory edid points to. The edid pointer must point to memory at least blocks * 128 bytes large (the size of one block is 128 bytes).

If there are fewer blocks than specified, then the driver will set blocks to the actual number of blocks. If there are no EDID blocks available at all, then the error code ENODATA is set.

If blocks have to be retrieved from the sink, then this call will block until they have been read.

If start_block and blocks are both set to 0 when VIDIOC_G_EDID is called, then the driver will set blocks to the total number of available EDID blocks and it will return 0 without copying any data. This is an easy way to discover how many EDID blocks there are.

Note

If there are no EDID blocks available at all, then the driver will set blocks to 0 and it returns 0.

To set the EDID blocks of a receiver the application has to fill in the pad, blocks and edid fields, set start_block to 0 and zero the reserved array. It is not possible to set part of an EDID, it is always all or nothing. Setting the EDID data is only valid for receivers as it makes no sense for a transmitter.

The driver assumes that the full EDID is passed in. If there are more EDID blocks than the hardware can handle then the EDID is not written, but instead the error code E2BIG is set and blocks is set to the maximum that the hardware supports. If start_block is any value other than 0 then the error code EINVAL is set.

To disable an EDID you set blocks to 0. Depending on the hardware this will drive the hotplug pin low and/or block the source from reading the EDID data in some way. In any case, the end result is the same: the EDID is no longer available.

v4l2_edid

struct v4l2_edid

__u32	pad	Pad for which to get/set the EDID blocks. When used with a video device node the pad represents the input or output index as returned by ioctl VIDIOC_ENUMINPUT and ioctl VIDIOC_ENUMOUTPUT respectively.
__u32	start_block	Read the EDID from starting with this block. Must be 0 when setting the EDID.
__u32	blocks	The number of blocks to get or set. Must be less or equal to 256 (the maximum number of blocks as defined by the standard). When you set the EDID and blocks is 0, then the EDID is disabled or erased.
__u32	reserved[5]	Reserved for future extensions. Applications and drivers must set the array to zero.
__u8 *	edid	Pointer to memory that contains the EDID. The minimum size is blocks * 128.

8.27.5. Return Value

On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.

ENODATA

The EDID data is not available.

E2BIG

The EDID data you provided is more than the hardware can handle.