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Date: Thu, 11 Feb 2021 15:14:23 +0200
From: Alexandru Ardelean <ardeleanalex@...il.com>
To: Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
linux-iio <linux-iio@...r.kernel.org>,
Lars-Peter Clausen <lars@...afoo.de>,
"Hennerich, Michael" <Michael.Hennerich@...log.com>,
Jonathan Cameron <jic23@...nel.org>,
Nuno Sá <nuno.sa@...log.com>,
"Bogdan, Dragos" <dragos.bogdan@...log.com>
Subject: Re: [PATCH 3/3] tools: iio: add example for high-speed buffer support
On Thu, Feb 11, 2021 at 2:38 PM Alexandru Ardelean
<alexandru.ardelean@...log.com> wrote:
>
> Following a recent update to the IIO buffer infrastructure, this change
> adds a basic example on how to access an IIO buffer via the new mmap()
> interface.
>
> The ioctl() for the high-speed mode needs to be enabled right from the
> start, before setting any parameters via sysfs (length, enable, etc), to
> make sure that the mmap mode is used and not the fileio mode.
>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
> ---
> tools/iio/iio_generic_buffer.c | 184 +++++++++++++++++++++++++++++++--
> 1 file changed, 178 insertions(+), 6 deletions(-)
>
> diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
> index fdd08514d556..af1a944edcdb 100644
> --- a/tools/iio/iio_generic_buffer.c
> +++ b/tools/iio/iio_generic_buffer.c
> @@ -31,6 +31,7 @@
> #include <stdbool.h>
> #include <signal.h>
> #include <sys/ioctl.h>
> +#include <sys/mman.h>
> #include <linux/iio/buffer.h>
> #include "iio_utils.h"
>
> @@ -239,6 +240,133 @@ static int enable_disable_all_channels(char *dev_dir_name, int buffer_idx, int e
> return 0;
> }
>
> +struct mmap_block {
> + struct iio_buffer_block block;
> + void *addr;
> +};
> +
> +static struct mmap_block *enable_high_speed(int buf_fd, unsigned int block_size,
> + int nblocks)
> +{
> + struct iio_buffer_block_alloc_req req = { 0 };
> + struct mmap_block *mmaps = NULL;
> + int mmaps_cnt = 0;
> + int i, ret;
> +
> + /**
> + * Validate we can do high-speed by issuing BLOCK_FREE ioctl.
> + * If using just BLOCK_ALLOC it's distinguish between ENOSYS
> + * and other error types.
> + */
> + ret = ioctl(buf_fd, IIO_BUFFER_BLOCK_FREE_IOCTL, 0);
> + if (ret < 0) {
> + errno = ENOSYS;
> + return NULL;
> + }
> +
> + /* for now, this */
> + req.id = 0;
> + req.type = 0;
> + req.size = block_size;
> + req.count = nblocks;
> +
> + ret = ioctl(buf_fd, IIO_BUFFER_BLOCK_ALLOC_IOCTL, &req);
> + if (ret < 0)
> + return NULL;
> +
> + if (req.count == 0) {
> + errno = ENOMEM;
> + return NULL;
> + }
> +
> + if (req.count < nblocks) {
> + fprintf(stderr, "Requested %d blocks, got %d\n",
> + nblocks, req.count);
> + errno = ENOMEM;
> + return NULL;
> + }
> +
> + mmaps = calloc(req.count, sizeof(*mmaps));
> + if (!mmaps) {
> + errno = ENOMEM;
> + return NULL;
> + }
> +
> + for (i = 0; i < req.count; i++) {
> + mmaps[i].block.id = i;
> + ret = ioctl(buf_fd, IIO_BUFFER_BLOCK_QUERY_IOCTL, &mmaps[i].block);
> + if (ret < 0)
> + goto error;
> +
> + ret = ioctl(buf_fd, IIO_BUFFER_BLOCK_ENQUEUE_IOCTL, &mmaps[i].block);
> + if (ret < 0)
> + goto error;
> +
> + mmaps[i].addr = mmap(0, mmaps[i].block.size,
> + PROT_READ | PROT_WRITE, MAP_SHARED,
> + buf_fd, mmaps[i].block.data.offset);
> +
> + if (mmaps[i].addr == MAP_FAILED)
> + goto error;
> +
> + mmaps_cnt++;
> + }
> +
> + return mmaps;
> +
> +error:
> + for (i = 0; i < mmaps_cnt; i++)
> + munmap(mmaps[i].addr, mmaps[i].block.size);
> + free(mmaps);
> + return NULL;
> +}
> +
> +static int read_high_speed(int buf_fd, char *data, unsigned int block_size,
> + struct mmap_block *mmaps, unsigned int mmaps_cnt)
> +{
> + struct iio_buffer_block block;
> + int ret;
> +
> + /**
> + * This is where some buffer-pool management can do wonders,
> + * but for the sake of this sample-code, we're just going to
> + * copy the data and re-enqueue it back
> + */
> + memset(&block, 0, sizeof(block));
> + ret = ioctl(buf_fd, IIO_BUFFER_BLOCK_DEQUEUE_IOCTL, &block);
> + if (ret < 0)
> + return ret;
> +
> + /* check for weird conditions */
> + if (block.bytes_used > block_size) {
> + fprintf(stderr,
> + "Got a bigger block (%u) than expected (%u)\n",
> + block.bytes_used, block_size);
> + return -EFBIG;
> + }
> +
> + if (block.bytes_used < block_size) {
> + /**
> + * This can be normal, with some real-world data
> + * terminating abruptly. But log it.
> + */
> + fprintf(stderr,
> + "Got a smaller block (%u) than expected (%u)\n",
> + block.bytes_used, block_size);
> + }
> +
> + /* memcpy() the data, we lose some more performance here :p */
> + memcpy(data, mmaps[block.id].addr, block.bytes_used);
> +
> + /* and re-queue this back */
> + ret = ioctl(buf_fd, IIO_BUFFER_BLOCK_ENQUEUE_IOCTL, &mmaps[block.id].block);
> + if (ret < 0)
> + return ret;
> +
> + return block.bytes_used;
> +}
> +
forgot to remove this extra line;
will make a note, for the next re-spin;
after some feedback
> +
> static void print_usage(void)
> {
> fprintf(stderr, "Usage: generic_buffer [options]...\n"
> @@ -249,6 +377,7 @@ static void print_usage(void)
> " -c <n> Do n conversions, or loop forever if n < 0\n"
> " -e Disable wait for event (new data)\n"
> " -g Use trigger-less mode\n"
> + " -h Use high-speed buffer access\n"
> " -l <n> Set buffer length to n samples\n"
> " --device-name -n <name>\n"
> " --device-num -N <num>\n"
> @@ -356,9 +485,15 @@ int main(int argc, char **argv)
>
> struct iio_channel_info *channels = NULL;
>
> + static bool use_high_speed = false;
> + unsigned int block_size;
> + int nblocks = 16; /* default */
> + int mmaps_cnt = 0;
> + struct mmap_block *mmaps = NULL;
> +
> register_cleanup();
>
> - while ((c = getopt_long(argc, argv, "aAb:c:egl:n:N:t:T:w:?", longopts,
> + while ((c = getopt_long(argc, argv, "aAb:c:eghl:n:N:t:T:w:?", longopts,
> NULL)) != -1) {
> switch (c) {
> case 'a':
> @@ -396,6 +531,9 @@ int main(int argc, char **argv)
> case 'g':
> notrigger = 1;
> break;
> + case 'h':
> + use_high_speed = true;
> + break;
> case 'l':
> errno = 0;
> buf_len = strtoul(optarg, &dummy, 10);
> @@ -661,6 +799,29 @@ int main(int argc, char **argv)
> goto error;
> }
>
> + scan_size = size_from_channelarray(channels, num_channels);
> + block_size = scan_size * buf_len;
> + /**
> + * Need to enable high-speed before configuring length/enable.
> + * Otherwise, the DMA buffer will work in fileio mode,
> + * and mmap won't work.
> + */
> + if (use_high_speed) {
> + /**
> + * The block_size for one block is the same as 'data', but it
> + * doesn't need to be the same size. It is easier for the sake
> + * of this example.
> + */
> + mmaps = enable_high_speed(buf_fd, block_size, nblocks);
> + if (!mmaps) {
> + fprintf(stderr, "Could not enable high-speed mode\n");
> + ret = -errno;
> + goto error;
> + }
> + mmaps_cnt = nblocks;
> + printf("Using high-speed mode\n");
> + }
> +
> /* Setup ring buffer parameters */
> ret = write_sysfs_int("length", buf_dir_name, buf_len);
> if (ret < 0)
> @@ -675,8 +836,7 @@ int main(int argc, char **argv)
> goto error;
> }
>
> - scan_size = size_from_channelarray(channels, num_channels);
> - data = malloc(scan_size * buf_len);
> + data = malloc(block_size);
> if (!data) {
> ret = -ENOMEM;
> goto error;
> @@ -719,7 +879,13 @@ int main(int argc, char **argv)
> toread = 64;
> }
>
> - read_size = read(buf_fd, data, toread * scan_size);
> + if (use_high_speed) {
> + read_size = read_high_speed(buf_fd, data, block_size,
> + mmaps, mmaps_cnt);
> + } else {
> + read_size = read(buf_fd, data, toread * scan_size);
> + }
> +
> if (read_size < 0) {
> if (errno == EAGAIN) {
> fprintf(stderr, "nothing available\n");
> @@ -738,8 +904,14 @@ int main(int argc, char **argv)
>
> if (fd >= 0 && close(fd) == -1)
> perror("Failed to close character device");
> - if (buf_fd >= 0 && close(buf_fd) == -1)
> - perror("Failed to close buffer");
> + for (i = 0; i < mmaps_cnt; i++)
> + munmap(mmaps[i].addr, mmaps[i].block.size);
> + free(mmaps);
> + if (buf_fd >= 0) {
> + ioctl(buf_fd, IIO_BUFFER_BLOCK_FREE_IOCTL, 0);
> + if (close(buf_fd) == -1)
> + perror("Failed to close buffer");
> + }
> free(buffer_access);
> free(data);
> free(buf_dir_name);
> --
> 2.17.1
>
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