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Date: Sun, 14 Feb 2021 16:21:35 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc: <linux-kernel@...r.kernel.org>, <linux-iio@...r.kernel.org>,
<lars@...afoo.de>, <Michael.Hennerich@...log.com>,
<nuno.sa@...log.com>, <dragos.bogdan@...log.com>
Subject: Re: [RFC PATCH 1/5] iio: Add output buffer support
On Fri, 12 Feb 2021 12:20:17 +0200
Alexandru Ardelean <alexandru.ardelean@...log.com> wrote:
> From: Lars-Peter Clausen <lars@...afoo.de>
>
> Currently IIO only supports buffer mode for capture devices like ADCs. Add
> support for buffered mode for output devices like DACs.
>
> The output buffer implementation is analogous to the input buffer
> implementation. Instead of using read() to get data from the buffer write()
> is used to copy data into the buffer.
>
> poll() with POLLOUT will wakeup if there is space available for more or
> equal to the configured watermark of samples.
>
> Drivers can remove data from a buffer using iio_buffer_remove_sample(), the
> function can e.g. called from a trigger handler to write the data to
> hardware.
>
> A buffer can only be either a output buffer or an input, but not both. So,
> for a device that has an ADC and DAC path, this will mean 2 IIO buffers
> (one for each direction).
>
> The direction of the buffer is decided by the new direction field of the
> iio_buffer struct and should be set after allocating and before registering
> it.
>
> Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
> ---
> drivers/iio/industrialio-buffer.c | 110 ++++++++++++++++++++++++++++--
> include/linux/iio/buffer.h | 7 ++
> include/linux/iio/buffer_impl.h | 11 +++
> 3 files changed, 124 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index a0d1ad86022f..6f4f5f5544f3 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -162,6 +162,69 @@ static ssize_t iio_buffer_read(struct file *filp, char __user *buf,
> return ret;
> }
>
> +static size_t iio_buffer_space_available(struct iio_buffer *buf)
> +{
> + if (buf->access->space_available)
> + return buf->access->space_available(buf);
> +
> + return SIZE_MAX;
> +}
> +
> +static ssize_t iio_buffer_write(struct file *filp, const char __user *buf,
> + size_t n, loff_t *f_ps)
> +{
> + struct iio_dev_buffer_pair *ib = filp->private_data;
> + struct iio_buffer *rb = ib->buffer;
> + struct iio_dev *indio_dev = ib->indio_dev;
> + DEFINE_WAIT_FUNC(wait, woken_wake_function);
> + size_t datum_size;
> + size_t to_wait;
> + int ret;
> +
> + if (!rb || !rb->access->write)
> + return -EINVAL;
> +
> + datum_size = rb->bytes_per_datum;
> +
> + /*
> + * If datum_size is 0 there will never be anything to read from the
> + * buffer, so signal end of file now.
> + */
> + if (!datum_size)
> + return 0;
> +
> + if (filp->f_flags & O_NONBLOCK)
> + to_wait = 0;
> + else
> + to_wait = min_t(size_t, n / datum_size, rb->watermark);
> +
> + add_wait_queue(&rb->pollq, &wait);
> + do {
> + if (!indio_dev->info) {
> + ret = -ENODEV;
> + break;
> + }
> +
> + if (iio_buffer_space_available(rb) < to_wait) {
In the non blocking case, we still hit here, but query for less than 0
which seems a bit pointless. in theory at least
iio_buffer_space_available() might be expensive. Can we save on that
query?
> + if (signal_pending(current)) {
> + ret = -ERESTARTSYS;
> + break;
> + }
> +
> + wait_woken(&wait, TASK_INTERRUPTIBLE,
> + MAX_SCHEDULE_TIMEOUT);
> + continue;
> + }
> +
> + ret = rb->access->write(rb, n, buf);
> + if (ret == 0 && (filp->f_flags & O_NONBLOCK))
> + ret = -EAGAIN;
> + } while (ret == 0);
> + remove_wait_queue(&rb->pollq, &wait);
> +
> + return ret;
> +}
> +
> /**
> * iio_buffer_poll() - poll the buffer to find out if it has data
> * @filp: File structure pointer for device access
> @@ -182,8 +245,19 @@ static __poll_t iio_buffer_poll(struct file *filp,
> return 0;
>
> poll_wait(filp, &rb->pollq, wait);
> - if (iio_buffer_ready(indio_dev, rb, rb->watermark, 0))
> - return EPOLLIN | EPOLLRDNORM;
> +
> + switch (rb->direction) {
> + case IIO_BUFFER_DIRECTION_IN:
> + if (iio_buffer_ready(indio_dev, rb, rb->watermark, 0))
> + return EPOLLIN | EPOLLRDNORM;
> + break;
> + case IIO_BUFFER_DIRECTION_OUT:
> + if (iio_buffer_space_available(rb) >= rb->watermark)
> + return EPOLLOUT | EPOLLWRNORM;
> + break;
> + }
> +
> + /* need a way of knowing if there may be enough data... */
> return 0;
> }
>
> @@ -232,6 +306,16 @@ void iio_buffer_wakeup_poll(struct iio_dev *indio_dev)
> }
> }
>
> +int iio_buffer_remove_sample(struct iio_buffer *buffer, u8 *data)
> +{
> + if (!buffer || !buffer->access)
> + return -EINVAL;
> + if (!buffer->access->write)
> + return -ENOSYS;
> + return buffer->access->remove_from(buffer, data);
> +}
> +EXPORT_SYMBOL_GPL(iio_buffer_remove_sample);
> +
> void iio_buffer_init(struct iio_buffer *buffer)
> {
> INIT_LIST_HEAD(&buffer->demux_list);
> @@ -803,6 +887,8 @@ static int iio_verify_update(struct iio_dev *indio_dev,
> }
>
> if (insert_buffer) {
> + if (insert_buffer->direction == IIO_BUFFER_DIRECTION_OUT)
> + strict_scanmask = true;
> bitmap_or(compound_mask, compound_mask,
> insert_buffer->scan_mask, indio_dev->masklength);
> scan_timestamp |= insert_buffer->scan_timestamp;
> @@ -945,6 +1031,8 @@ static int iio_update_demux(struct iio_dev *indio_dev)
> int ret;
>
> list_for_each_entry(buffer, &iio_dev_opaque->buffer_list, buffer_list) {
> + if (buffer->direction == IIO_BUFFER_DIRECTION_OUT)
> + continue;
> ret = iio_buffer_update_demux(indio_dev, buffer);
> if (ret < 0)
> goto error_clear_mux_table;
> @@ -1155,6 +1243,11 @@ int iio_update_buffers(struct iio_dev *indio_dev,
> mutex_lock(&indio_dev->info_exist_lock);
> mutex_lock(&indio_dev->mlock);
>
> + if (insert_buffer->direction == IIO_BUFFER_DIRECTION_OUT) {
> + ret = -EINVAL;
> + goto out_unlock;
> + }
> +
> if (insert_buffer && iio_buffer_is_active(insert_buffer))
> insert_buffer = NULL;
>
> @@ -1400,6 +1493,7 @@ static const struct file_operations iio_buffer_chrdev_fileops = {
> .owner = THIS_MODULE,
> .llseek = noop_llseek,
> .read = iio_buffer_read,
> + .write = iio_buffer_write,
> .poll = iio_buffer_poll,
> .unlocked_ioctl = iio_buffer_ioctl,
> .compat_ioctl = compat_ptr_ioctl,
> @@ -1914,8 +2008,16 @@ static int iio_buffer_mmap(struct file *filep, struct vm_area_struct *vma)
> if (!(vma->vm_flags & VM_SHARED))
> return -EINVAL;
>
> - if (!(vma->vm_flags & VM_READ))
> - return -EINVAL;
> + switch (buffer->direction) {
> + case IIO_BUFFER_DIRECTION_IN:
> + if (!(vma->vm_flags & VM_READ))
> + return -EINVAL;
> + break;
> + case IIO_BUFFER_DIRECTION_OUT:
> + if (!(vma->vm_flags & VM_WRITE))
> + return -EINVAL;
> + break;
> + }
>
> return buffer->access->mmap(buffer, vma);
> }
> diff --git a/include/linux/iio/buffer.h b/include/linux/iio/buffer.h
> index b6928ac5c63d..e87b8773253d 100644
> --- a/include/linux/iio/buffer.h
> +++ b/include/linux/iio/buffer.h
> @@ -11,8 +11,15 @@
>
> struct iio_buffer;
>
> +enum iio_buffer_direction {
> + IIO_BUFFER_DIRECTION_IN,
> + IIO_BUFFER_DIRECTION_OUT,
> +};
> +
> int iio_push_to_buffers(struct iio_dev *indio_dev, const void *data);
>
> +int iio_buffer_remove_sample(struct iio_buffer *buffer, u8 *data);
> +
> /**
> * iio_push_to_buffers_with_timestamp() - push data and timestamp to buffers
> * @indio_dev: iio_dev structure for device.
> diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
> index 1d57dc7ccb4f..47bdbf4a4519 100644
> --- a/include/linux/iio/buffer_impl.h
> +++ b/include/linux/iio/buffer_impl.h
> @@ -7,6 +7,7 @@
> #ifdef CONFIG_IIO_BUFFER
>
> #include <uapi/linux/iio/buffer.h>
> +#include <linux/iio/buffer.h>
>
> struct iio_dev;
> struct iio_buffer;
> @@ -23,6 +24,10 @@ struct iio_buffer;
> * @read: try to get a specified number of bytes (must exist)
> * @data_available: indicates how much data is available for reading from
> * the buffer.
> + * @remove_from: remove sample from buffer. Drivers should calls this to
> + * remove a sample from a buffer.
> + * @write: try to write a number of bytes
> + * @space_available: returns the amount of bytes available in a buffer
> * @request_update: if a parameter change has been marked, update underlying
> * storage.
> * @set_bytes_per_datum:set number of bytes per datum
> @@ -61,6 +66,9 @@ struct iio_buffer_access_funcs {
> int (*store_to)(struct iio_buffer *buffer, const void *data);
> int (*read)(struct iio_buffer *buffer, size_t n, char __user *buf);
> size_t (*data_available)(struct iio_buffer *buffer);
> + int (*remove_from)(struct iio_buffer *buffer, void *data);
> + int (*write)(struct iio_buffer *buffer, size_t n, const char __user *buf);
> + size_t (*space_available)(struct iio_buffer *buffer);
>
> int (*request_update)(struct iio_buffer *buffer);
>
> @@ -103,6 +111,9 @@ struct iio_buffer {
> /** @bytes_per_datum: Size of individual datum including timestamp. */
> size_t bytes_per_datum;
>
> + /* @direction: Direction of the data stream (in/out). */
> + enum iio_buffer_direction direction;
> +
> /**
> * @access: Buffer access functions associated with the
> * implementation.
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