Date:   Fri, 8 Oct 2021 09:56:29 +0300
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     "Chindris, Mihail" <Mihail.Chindris@...log.com>,
        "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 <aardelean@...iqon.com>
Subject: Re: [PATCH v6 1/6] iio: Add output buffer support

On Thu, Oct 7, 2021 at 8:09 PM Jonathan Cameron <jic23@...nel.org> wrote:
>
> On Thu, 7 Oct 2021 16:24:52 +0000
> "Chindris, Mihail" <Mihail.Chindris@...log.com> wrote:
>
> > > -----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/source/
> > > 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 :)
>
> Alex / Lars, what would you consider a fair way to represent this?

I'm fine with whatever representation you (Jonathan) consider.
I'm fine with either tag.

My main contribution here is that the "direction" parameter is part of
"struct iio_buffer", whereas Lars' implementation made it part of
"struct iio_dev".

I seem to recall that there was an "iio_buffer->direction"
implementation before the "iio_dev->direction" in the ADI kernel tree.
Maybe there was some change of mind somewhere.
But the history was pretty messy in those early days (at least that's
what the "git log" told me), as IIO was also moved out of staging and
heavy development was being done.

In any case, this patch works on top of the new multi-buffer support.
Which would mean that with this patch, a new class of ADDAC devices
(not sure how popular they are these days) can be supported.
As well as some basic transceivers.

>
> (added some working addresses for Alex...)
>
>
> >
> > Mihail
> >
> > >
> > > > ---
> > > >  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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