7.6. ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER¶
VIDIOC_DBG_G_REGISTER - VIDIOC_DBG_S_REGISTER - Read or write hardware registers
int ioctl(int fd, VIDIOC_DBG_G_REGISTER, struct v4l2_dbg_register *argp)
int ioctl(int fd, VIDIOC_DBG_S_REGISTER, const struct v4l2_dbg_register *argp)
- File descriptor returned by
- Pointer to struct
This is an Experimental API Elements interface and may change in the future.
For driver debugging purposes these ioctls allow test applications to access hardware registers directly. Regular applications must not use them.
Since writing or even reading registers can jeopardize the system
security, its stability and damage the hardware, both ioctls require
superuser privileges. Additionally the Linux kernel must be compiled
CONFIG_VIDEO_ADV_DEBUG option to enable these ioctls.
To write a register applications must initialize all fields of a struct
v4l2_dbg_register except for
VIDIOC_DBG_S_REGISTER with a pointer to this structure. The
match.name fields select a chip
on the TV card, the
reg field specifies a register number and the
val field the value to be written into the register.
To read a register applications must initialize the
reg fields, and call
VIDIOC_DBG_G_REGISTER with a pointer to this structure. On success
the driver stores the register value in the
val field and the size
(in bytes) of the value in
selects the nth non-sub-device chip on the TV card. The number zero
always selects the host chip, e. g. the chip connected to the PCI or USB
bus. You can find out which chips are present with the
ioctl VIDIOC_DBG_G_CHIP_INFO ioctl.
selects the nth sub-device.
These ioctls are optional, not all drivers may support them. However
when a driver supports these ioctls it must also support
ioctl VIDIOC_DBG_G_CHIP_INFO. Conversely
it may support
VIDIOC_DBG_G_CHIP_INFO but not these ioctls.
VIDIOC_DBG_S_REGISTER were introduced
in Linux 2.6.21, but their API was changed to the one described here in
We recommended the v4l2-dbg utility over calling these ioctls directly. It is available from the LinuxTV v4l-dvb repository; see https://linuxtv.org/repo/ for access instructions.
||See Chip Match Types for a list of possible types.|
||Match a chip by this number, interpreted according to the
||Match a chip by this name, interpreted according to the
||How to match the chip, see
||The register size in bytes.|
||A register number.|
||The value read from, or to be written into the register.|
||0||Match the nth chip on the card, zero for the bridge chip. Does not match sub-devices.|
||4||Match the nth sub-device.|
7.6.5. 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.
- Insufficient permissions. Root privileges are required to execute these ioctls.