ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER &manvol; VIDIOC_DBG_G_REGISTER VIDIOC_DBG_S_REGISTER Read or write hardware registers int ioctl int fd int request struct v4l2_dbg_register *argp int ioctl int fd int request const struct v4l2_dbg_register *argp fd &fd; request VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER argp This is an experimental 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 with the CONFIG_VIDEO_ADV_DEBUG option to enable these ioctls. To write a register applications must initialize all fields of a &v4l2-dbg-register; except for size and call VIDIOC_DBG_S_REGISTER with a pointer to this structure. The match.type and match.addr or 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 match.type, match.addr or match.name and 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 size. When match.type is V4L2_CHIP_MATCH_BRIDGE, match.addr selects the nth non-sub-device chip on the TV card. The number zero always selects the host chip, ⪚ the chip connected to the PCI or USB bus. You can find out which chips are present with the &VIDIOC-DBG-G-CHIP-INFO; ioctl. When match.type is V4L2_CHIP_MATCH_I2C_DRIVER, match.name contains the I2C driver name. For instance "saa7127" will match any chip supported by the saa7127 driver, regardless of its &i2c; bus address. When multiple chips supported by the same driver are present, the effect of these ioctls is undefined. Again with the &VIDIOC-DBG-G-CHIP-INFO; ioctl you can find out which &i2c; chips are present. When match.type is V4L2_CHIP_MATCH_I2C_ADDR, match.addr selects a chip by its 7 bit &i2c; bus address. When match.type is V4L2_CHIP_MATCH_AC97, match.addr selects the nth AC97 chip on the TV card. When match.type is V4L2_CHIP_MATCH_SUBDEV, match.addr selects the nth sub-device. Due to a flaw in the Linux &i2c; bus driver these ioctls may return successfully without actually reading or writing a register. To catch the most likely failure we recommend a &VIDIOC-DBG-G-CHIP-INFO; call confirming the presence of the selected &i2c; chip. These ioctls are optional, not all drivers may support them. However when a driver supports these ioctls it must also support &VIDIOC-DBG-G-CHIP-INFO;. Conversely it may support VIDIOC_DBG_G_CHIP_INFO but not these ioctls. VIDIOC_DBG_G_REGISTER and VIDIOC_DBG_S_REGISTER were introduced in Linux 2.6.21, but their API was changed to the one described here in kernel 2.6.29. We recommended the v4l2-dbg utility over calling these ioctls directly. It is available from the LinuxTV v4l-dvb repository; see http://linuxtv.org/repo/ for access instructions. &cs-ustr; __u32 type See for a list of possible types. union (anonymous) __u32 addr Match a chip by this number, interpreted according to the type field. char name[32] Match a chip by this name, interpreted according to the type field. struct v4l2_dbg_match match How to match the chip, see . __u32 size The register size in bytes. __u64 reg A register number. __u64 val The value read from, or to be written into the register. &cs-def; V4L2_CHIP_MATCH_BRIDGE 0 Match the nth chip on the card, zero for the bridge chip. Does not match sub-devices. V4L2_CHIP_MATCH_I2C_DRIVER 1 Match an &i2c; chip by its driver name. V4L2_CHIP_MATCH_I2C_ADDR 2 Match a chip by its 7 bit &i2c; bus address. V4L2_CHIP_MATCH_AC97 3 Match the nth anciliary AC97 chip. V4L2_CHIP_MATCH_SUBDEV 4 Match the nth sub-device. &return-value; EPERM Insufficient permissions. Root privileges are required to execute these ioctls.