include/uapi/linux/iio/buffer.h

/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
/* industrial I/O buffer definitions needed both in and out of kernel
 */

#ifndef _UAPI_IIO_BUFFER_H_
#define _UAPI_IIO_BUFFER_H_

#define IIO_BUFFER_GET_FD_IOCTL			_IOWR('i', 0x91, int)

#endif /* _UAPI_IIO_BUFFER_H_ */
iio: buffer: add ioctl() to support opening extra buffers for IIO device With this change, an ioctl() call is added to open a character device for a buffer. The ioctl() number is 'i' 0x91, which follows the IIO_GET_EVENT_FD_IOCTL ioctl. The ioctl() will return an FD for the requested buffer index. The indexes are the same from the /sys/iio/devices/iio:deviceX/bufferY (i.e. the Y variable). Since there doesn't seem to be a sane way to return the FD for buffer0 to be the same FD for the /dev/iio:deviceX, this ioctl() will return another FD for buffer0 (or the first buffer). This duplicate FD will be able to access the same buffer object (for buffer0) as accessing directly the /dev/iio:deviceX chardev. Also, there is no IIO_BUFFER_GET_BUFFER_COUNT ioctl() implemented, as the index for each buffer (and the count) can be deduced from the '/sys/bus/iio/devices/iio:deviceX/bufferY' folders (i.e the number of bufferY folders). Used following C code to test this: ------------------------------------------------------------------- #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/ioctl.h> #include <fcntl.h" #include <errno.h> #define IIO_BUFFER_GET_FD_IOCTL _IOWR('i', 0x91, int) int main(int argc, char *argv[]) { int fd; int fd1; int ret; if ((fd = open("/dev/iio:device0", O_RDWR))<0) { fprintf(stderr, "Error open() %d errno %d\n",fd, errno); return -1; } fprintf(stderr, "Using FD %d\n", fd); fd1 = atoi(argv[1]); ret = ioctl(fd, IIO_BUFFER_GET_FD_IOCTL, &fd1); if (ret < 0) { fprintf(stderr, "Error for buffer %d ioctl() %d errno %d\n", fd1, ret, errno); close(fd); return -1; } fprintf(stderr, "Got FD %d\n", fd1); close(fd1); close(fd); return 0; } ------------------------------------------------------------------- Results are: ------------------------------------------------------------------- # ./test 0 Using FD 3 Got FD 4 # ./test 1 Using FD 3 Got FD 4 # ./test 2 Using FD 3 Got FD 4 # ./test 3 Using FD 3 Got FD 4 # ls /sys/bus/iio/devices/iio\:device0 buffer buffer0 buffer1 buffer2 buffer3 dev in_voltage_sampling_frequency in_voltage_scale in_voltage_scale_available name of_node power scan_elements subsystem uevent ------------------------------------------------------------------- iio:device0 has some fake kfifo buffers attached to an IIO device. Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com> Link: https://lore.kernel.org/r/20210215104043.91251-21-alexandru.ardelean@analog.com Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> 2021-02-15 12:40:39 +02:00			`/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */`
			`/* industrial I/O buffer definitions needed both in and out of kernel`
			`*/`

			`#ifndef _UAPI_IIO_BUFFER_H_`
			`#define _UAPI_IIO_BUFFER_H_`

			`#define IIO_BUFFER_GET_FD_IOCTL _IOWR('i', 0x91, int)`

			`#endif /* _UAPI_IIO_BUFFER_H_ */`