Date:   Thu, 7 Oct 2021 17:04:05 +0000
From:   "Chindris, Mihail" <Mihail.Chindris@...log.com>
To:     Jonathan Cameron <jic23@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "lars@...afoo.de" <lars@...afoo.de>,
        "Hennerich, Michael" <Michael.Hennerich@...log.com>,
        "Sa, Nuno" <Nuno.Sa@...log.com>,
        "Bogdan, Dragos" <Dragos.Bogdan@...log.com>,
        Alexandru Ardelean <ardeleanalex@...il.com>
Subject: RE: [PATCH v6 1/6] iio: Add output buffer support

> -----Original Message-----
> From: Chindris, Mihail
> Sent: Thursday, 7 October 2021 19:25
> To: Jonathan Cameron <jic23@...nel.org>
> Cc: linux-kernel@...r.kernel.org; linux-iio@...r.kernel.org;
> lars@...afoo.de; Hennerich, Michael <Michael.Hennerich@...log.com>;
> Sa, Nuno <Nuno.Sa@...log.com>; Bogdan, Dragos
> <Dragos.Bogdan@...log.com>; alexandru.ardelean@...log.com
> Subject: RE: [PATCH v6 1/6] iio: Add output buffer support
> 
> > -----Original Message-----
> > From: Jonathan Cameron <jic23@...nel.org>
> > Sent: Thursday, 7 October 2021 19:06
> > To: Chindris, Mihail <Mihail.Chindris@...log.com>
> > Cc: linux-kernel@...r.kernel.org; linux-iio@...r.kernel.org;
> > lars@...afoo.de; Hennerich, Michael <Michael.Hennerich@...log.com>;
> > Sa, Nuno <Nuno.Sa@...log.com>; Bogdan, Dragos
> > <Dragos.Bogdan@...log.com>; alexandru.ardelean@...log.com
> > Subject: Re: [PATCH v6 1/6] iio: Add output buffer support
> >
> > On Thu, 7 Oct 2021 08:00:30 +0000
> > Mihail Chindris <mihail.chindris@...log.com> wrote:
> >
> > > 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.
> > >
> > > Drivers can remove data from a buffer using iio_pop_from_buffer(),
> > > 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>
> > > Signed-off-by: Mihail Chindris <mihail.chindris@...log.com>
> >
> > Hi Mihail,
> >
> > I'm fine with this series now, but one question for this patch on
> > whether we can clarify the author chain.
> >
> > The above might mean one of two things.
> > 1) Lars wrote the code and Alex and yourself just 'handled' the patch on its
> >    way to posting.  If that were the case it should have a From: for
> > Lars
> > 2) All 3 were involved in changes to this patch.  In that case we
> > should have
> > Co-developed-by: lines for lars and Alex as described:
> > https://urldefense.com/v3/__https://elixir.bootlin.com/linux/latest/so
> > urce/
> > Documentation/process/submitting-
> > patches.rst*L475__;Iw!!A3Ni8CS0y2Y!t1IaOEZX3w2pZXl-
> > RyAlXgPPvxFtCON74ppfGuMgV_pKZcNjsLs-dKSk_mA34IsmlOU$
> >
> > This patch has a history well predating the Co-developed-tag but I'm
> > happy to add that if you can confirm that matches with the intent.
> >
> > Good to leave on the list for a few days anyway in case anyone else
> > wants to take a quick look.
> >
> > I'm looking forwards to merging this and thinking back to when Lars
> > originally discussed this feature with me rather a lot of years back!
> >
> > Jonathan
> >
> >
> 
> Hi Jonathan,
> 
> What I have done with the patch was to take the V3 that Alex has left and
> implement the feedback. So I think this is considered as 'handled' from my
> side.
> What happened before V3 I think is better if Alex spokes for himself because
> I don't really know :)
> 
> Mihail
> 

CC: Alexandru Ardelean <ardeleanalex@...il.com>

> >
> > > ---
> > >  drivers/iio/iio_core.h            |   4 +
> > >  drivers/iio/industrialio-buffer.c | 127
> > +++++++++++++++++++++++++++++-
> > >  drivers/iio/industrialio-core.c   |   1 +
> > >  include/linux/iio/buffer.h        |   7 ++
> > >  include/linux/iio/buffer_impl.h   |  11 +++
> > >  5 files changed, 148 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/iio/iio_core.h b/drivers/iio/iio_core.h index
> > > 8f4a9b264962..61e318431de9 100644
> > > --- a/drivers/iio/iio_core.h
> > > +++ b/drivers/iio/iio_core.h
> > > @@ -68,12 +68,15 @@ __poll_t iio_buffer_poll_wrapper(struct file *filp,
> > >  				 struct poll_table_struct *wait);  ssize_t
> > > iio_buffer_read_wrapper(struct file *filp, char __user *buf,
> > >  				size_t n, loff_t *f_ps);
> > > +ssize_t iio_buffer_write_wrapper(struct file *filp, const char __user
> *buf,
> > > +				 size_t n, loff_t *f_ps);
> > >
> > >  int iio_buffers_alloc_sysfs_and_mask(struct iio_dev *indio_dev);
> > > void iio_buffers_free_sysfs_and_mask(struct iio_dev *indio_dev);
> > >
> > >  #define iio_buffer_poll_addr (&iio_buffer_poll_wrapper)  #define
> > > iio_buffer_read_outer_addr (&iio_buffer_read_wrapper)
> > > +#define iio_buffer_write_outer_addr (&iio_buffer_write_wrapper)
> > >
> > >  void iio_disable_all_buffers(struct iio_dev *indio_dev);  void
> > > iio_buffer_wakeup_poll(struct iio_dev *indio_dev); @@ -83,6 +86,7 @@
> > > void iio_device_detach_buffers(struct iio_dev *indio_dev);
> > >
> > >  #define iio_buffer_poll_addr NULL
> > >  #define iio_buffer_read_outer_addr NULL
> > > +#define iio_buffer_write_outer_addr NULL
> > >
> > >  static inline int iio_buffers_alloc_sysfs_and_mask(struct iio_dev
> > > *indio_dev)  { diff --git a/drivers/iio/industrialio-buffer.c
> > > b/drivers/iio/industrialio-buffer.c
> > > index a95cc2da56be..7286563e6234 100644
> > > --- a/drivers/iio/industrialio-buffer.c
> > > +++ b/drivers/iio/industrialio-buffer.c
> > > @@ -120,6 +120,9 @@ static ssize_t iio_buffer_read(struct file
> > > *filp, char
> > __user *buf,
> > >  	if (!rb || !rb->access->read)
> > >  		return -EINVAL;
> > >
> > > +	if (rb->direction != IIO_BUFFER_DIRECTION_IN)
> > > +		return -EPERM;
> > > +
> > >  	datum_size = rb->bytes_per_datum;
> > >
> > >  	/*
> > > @@ -161,6 +164,65 @@ 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);
> > > +	int ret;
> > > +	size_t written;
> > > +
> > > +	if (!indio_dev->info)
> > > +		return -ENODEV;
> > > +
> > > +	if (!rb || !rb->access->write)
> > > +		return -EINVAL;
> > > +
> > > +	if (rb->direction != IIO_BUFFER_DIRECTION_OUT)
> > > +		return -EPERM;
> > > +
> > > +	written = 0;
> > > +	add_wait_queue(&rb->pollq, &wait);
> > > +	do {
> > > +		if (indio_dev->info == NULL)
> > > +			return -ENODEV;
> > > +
> > > +		if (!iio_buffer_space_available(rb)) {
> > > +			if (signal_pending(current)) {
> > > +				ret = -ERESTARTSYS;
> > > +				break;
> > > +			}
> > > +
> > > +			wait_woken(&wait, TASK_INTERRUPTIBLE,
> > > +					MAX_SCHEDULE_TIMEOUT);
> > > +			continue;
> > > +		}
> > > +
> > > +		ret = rb->access->write(rb, n - written, buf + written);
> > > +		if (ret == 0 && (filp->f_flags & O_NONBLOCK))
> > > +			ret = -EAGAIN;
> > > +
> > > +		if (ret > 0) {
> > > +			written += ret;
> > > +			if (written != n && !(filp->f_flags & O_NONBLOCK))
> > > +				continue;
> > > +		}
> > > +	} while (ret == 0);
> > > +	remove_wait_queue(&rb->pollq, &wait);
> > > +
> > > +	return ret < 0 ? ret : n;
> > > +}
> > > +
> > >  /**
> > >   * iio_buffer_poll() - poll the buffer to find out if it has data
> > >   * @filp:	File structure pointer for device access
> > > @@ -181,8 +243,18 @@ 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))
> > > +			return EPOLLOUT | EPOLLWRNORM;
> > > +		break;
> > > +	}
> > > +
> > >  	return 0;
> > >  }
> > >
> > > @@ -199,6 +271,19 @@ ssize_t iio_buffer_read_wrapper(struct file
> > > *filp,
> > char __user *buf,
> > >  	return iio_buffer_read(filp, buf, n, f_ps);  }
> > >
> > > +ssize_t iio_buffer_write_wrapper(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;
> > > +
> > > +	/* check if buffer was opened through new API */
> > > +	if (test_bit(IIO_BUSY_BIT_POS, &rb->flags))
> > > +		return -EBUSY;
> > > +
> > > +	return iio_buffer_write(filp, buf, n, f_ps); }
> > > +
> > >  __poll_t iio_buffer_poll_wrapper(struct file *filp,
> > >  				 struct poll_table_struct *wait)  { @@ -231,6
> +316,15 @@ void
> > > iio_buffer_wakeup_poll(struct iio_dev
> > *indio_dev)
> > >  	}
> > >  }
> > >
> > > +int iio_pop_from_buffer(struct iio_buffer *buffer, void *data) {
> > > +	if (!buffer || !buffer->access || !buffer->access->remove_from)
> > > +		return -EINVAL;
> > > +
> > > +	return buffer->access->remove_from(buffer, data); }
> > > +EXPORT_SYMBOL_GPL(iio_pop_from_buffer);
> > > +
> > >  void iio_buffer_init(struct iio_buffer *buffer)  {
> > >  	INIT_LIST_HEAD(&buffer->demux_list);
> > > @@ -1156,6 +1250,10 @@ int iio_update_buffers(struct iio_dev
> > *indio_dev,
> > >  	if (insert_buffer == remove_buffer)
> > >  		return 0;
> > >
> > > +	if (insert_buffer &&
> > > +	    (insert_buffer->direction == IIO_BUFFER_DIRECTION_OUT))
> > > +		return -EINVAL;
> > > +
> > >  	mutex_lock(&iio_dev_opaque->info_exist_lock);
> > >  	mutex_lock(&indio_dev->mlock);
> > >
> > > @@ -1277,6 +1375,22 @@ static ssize_t
> > iio_dma_show_data_available(struct device *dev,
> > >  	return sysfs_emit(buf, "%zu\n",
> > > iio_buffer_data_available(buffer));
> > >  }
> > >
> > > +static ssize_t direction_show(struct device *dev,
> > > +			      struct device_attribute *attr,
> > > +			      char *buf)
> > > +{
> > > +	struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > > +
> > > +	switch (buffer->direction) {
> > > +	case IIO_BUFFER_DIRECTION_IN:
> > > +		return sprintf(buf, "in\n");
> > > +	case IIO_BUFFER_DIRECTION_OUT:
> > > +		return sprintf(buf, "out\n");
> > > +	default:
> > > +		return -EINVAL;
> > > +	}
> > > +}
> > > +
> > >  static DEVICE_ATTR(length, S_IRUGO | S_IWUSR,
> iio_buffer_read_length,
> > >  		   iio_buffer_write_length);
> > >  static struct device_attribute dev_attr_length_ro = __ATTR(length,
> > > @@
> > > -1289,12 +1403,20 @@ static struct device_attribute
> > dev_attr_watermark_ro = __ATTR(watermark,
> > >  	S_IRUGO, iio_buffer_show_watermark, NULL);  static
> > > DEVICE_ATTR(data_available, S_IRUGO,
> > >  		iio_dma_show_data_available, NULL);
> > > +static DEVICE_ATTR_RO(direction);
> > >
> > > +/*
> > > + * When adding new attributes here, put the at the end, at least
> > > +until
> > > + * the code that handles the length/length_ro &
> > > +watermark/watermark_ro
> > > + * assignments gets cleaned up. Otherwise these can create some
> > > +weird
> > > + * duplicate attributes errors under some setups.
> > > + */
> > >  static struct attribute *iio_buffer_attrs[] = {
> > >  	&dev_attr_length.attr,
> > >  	&dev_attr_enable.attr,
> > >  	&dev_attr_watermark.attr,
> > >  	&dev_attr_data_available.attr,
> > > +	&dev_attr_direction.attr,
> > >  };
> > >
> > >  #define to_dev_attr(_attr) container_of(_attr, struct
> > > device_attribute, attr) @@ -1397,6 +1519,7 @@ 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,
> > >  	.release = iio_buffer_chrdev_release,  }; diff --git
> > > a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> > > index 2dbb37e09b8c..537a08549a69 100644
> > > --- a/drivers/iio/industrialio-core.c
> > > +++ b/drivers/iio/industrialio-core.c
> > > @@ -1822,6 +1822,7 @@ static const struct file_operations
> > iio_buffer_fileops = {
> > >  	.owner = THIS_MODULE,
> > >  	.llseek = noop_llseek,
> > >  	.read = iio_buffer_read_outer_addr,
> > > +	.write = iio_buffer_write_outer_addr,
> > >  	.poll = iio_buffer_poll_addr,
> > >  	.unlocked_ioctl = iio_ioctl,
> > >  	.compat_ioctl = compat_ptr_ioctl,
> > > diff --git a/include/linux/iio/buffer.h b/include/linux/iio/buffer.h
> > > index b6928ac5c63d..fe2e680d9b5e 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_pop_from_buffer(struct iio_buffer *buffer, void *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 245b32918ae1..e2ca8ea23e19
> > > 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 scan from buffer. Drivers should calls
> this to
> > > + *			remove a scan 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 @@ -49,6
> > +54,9
> > > @@ 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);
> > >
> > > @@ -80,6 +88,9 @@ 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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