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From:   Alexandru Ardelean <ardeleanalex@gmail.com>
Date:   Sun, 14 Feb 2021 16:37:23 +0200
Message-ID: <CA+U=Dsq=aD0J0u7QmXfFt5r9qeK2Z4y_sH+FtXNvu_hxpxnmiA@mail.gmail.com>
Subject: Re: [PATCH v5 12/17] iio: buffer: introduce support for attaching
 more IIO buffers
To:     Jonathan Cameron <jic23@kernel.org>
Cc:     Alexandru Ardelean <alexandru.ardelean@analog.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-iio <linux-iio@vger.kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        "Hennerich, Michael" <Michael.Hennerich@analog.com>,
        =?UTF-8?B?TnVubyBTw6E=?= <nuno.sa@analog.com>,
        "Bogdan, Dragos" <dragos.bogdan@analog.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Content-Type: text/plain; charset="UTF-8"
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On Sun, Feb 14, 2021 at 4:02 PM Alexandru Ardelean
<ardeleanalex@gmail.com> wrote:
>
> On Sun, Feb 14, 2021 at 3:21 PM Jonathan Cameron <jic23@kernel.org> wrote:
> >
> > On Thu, 11 Feb 2021 14:24:47 +0200
> > Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:
> >
> > > With this change, calling iio_device_attach_buffer() will actually attach
> > > more buffers.
> > > Right now this doesn't do any validation of whether a buffer is attached
> > > twice; maybe that can be added later (if needed). Attaching a buffer more
> > > than once should yield noticeably bad results.
> > >
> > > The first buffer is the legacy buffer, so a reference is kept to it.
> > >
> > > At this point, accessing the data for the extra buffers (that are added
> > > after the first one) isn't possible yet.
> > >
> > > The iio_device_attach_buffer() is also changed to return an error code,
> > > which for now is -ENOMEM if the array could not be realloc-ed for more
> > > buffers.
> >
> > This is called from a bunch of places, so we need to add error handling
> > for those which isn't currently present.
> >
> > Now arguably it is unlikely to fail, so I'm not that bothered about seeing
> > them all in place as part of this series, but I would like the handling
> > to have been posted at least.
>
> I know what you're referring to.
> I have a slightly better approach before updating this.
> I was going to send it a little later.
> I wanted to send it earlier, but I wanted to avoid overlapping myself
> with too many patches.
> Let me send something now [since it is ready].

So, coming back here.
See series [1]:
https://lore.kernel.org/linux-iio/20210214143313.67202-1-alexandru.ardelean@analog.com/T/#t

I could probably re-spin this series on top of series [1].
That would make things cleaner in terms of handling
iio_device_attach_buffer() in just 2 places I think.

>
> >
> > Otherwise, a few passing comments in here, but nothing to actually change.
> >
> >
> > Jonathan
> >
> > >
> > > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> > > ---
> > >  drivers/iio/iio_core.h            |  2 +
> > >  drivers/iio/industrialio-buffer.c | 96 +++++++++++++++++++++++++------
> > >  drivers/iio/industrialio-core.c   |  6 +-
> > >  include/linux/iio/buffer.h        |  4 +-
> > >  include/linux/iio/buffer_impl.h   |  3 +
> > >  include/linux/iio/iio-opaque.h    |  4 ++
> > >  6 files changed, 93 insertions(+), 22 deletions(-)
> > >
> > > diff --git a/drivers/iio/iio_core.h b/drivers/iio/iio_core.h
> > > index 87868fff7d37..4690c3240a5d 100644
> > > --- a/drivers/iio/iio_core.h
> > > +++ b/drivers/iio/iio_core.h
> > > @@ -77,6 +77,7 @@ void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev);
> > >
> > >  void iio_disable_all_buffers(struct iio_dev *indio_dev);
> > >  void iio_buffer_wakeup_poll(struct iio_dev *indio_dev);
> > > +void iio_buffers_put(struct iio_dev *indio_dev);
> > >
> > >  #else
> > >
> > > @@ -92,6 +93,7 @@ static inline void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev) {}
> > >
> > >  static inline void iio_disable_all_buffers(struct iio_dev *indio_dev) {}
> > >  static inline void iio_buffer_wakeup_poll(struct iio_dev *indio_dev) {}
> > > +static inline void iio_buffers_put(struct iio_dev *indio_dev) {}
> > >
> > >  #endif
> > >
> > > diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> > > index 209b3a32bdbb..1e8e4c2ff00e 100644
> > > --- a/drivers/iio/industrialio-buffer.c
> > > +++ b/drivers/iio/industrialio-buffer.c
> > > @@ -193,12 +193,14 @@ __poll_t iio_buffer_poll(struct file *filp,
> > >   */
> > >  void iio_buffer_wakeup_poll(struct iio_dev *indio_dev)
> > >  {
> > > -     struct iio_buffer *buffer = indio_dev->buffer;
> > > -
> > > -     if (!buffer)
> > > -             return;
> > > +     struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > > +     struct iio_buffer *buffer;
> > > +     unsigned int i;
> > >
> > > -     wake_up(&buffer->pollq);
> > > +     for (i = 0; i < iio_dev_opaque->attached_buffers_cnt; i++) {
> > > +             buffer = iio_dev_opaque->attached_buffers[i];
> > > +             wake_up(&buffer->pollq);
> > > +     }
> > >  }
> > >
> > >  void iio_buffer_init(struct iio_buffer *buffer)
> > > @@ -212,6 +214,18 @@ void iio_buffer_init(struct iio_buffer *buffer)
> > >  }
> > >  EXPORT_SYMBOL(iio_buffer_init);
> > >
> > > +void iio_buffers_put(struct iio_dev *indio_dev)
> > > +{
> > > +     struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > > +     struct iio_buffer *buffer;
> > > +     unsigned int i;
> > > +
> > > +     for (i = 0; i < iio_dev_opaque->attached_buffers_cnt; i++) {
> > > +             buffer = iio_dev_opaque->attached_buffers[i];
> > > +             iio_buffer_put(buffer);
> > > +     }
> > > +}
> > > +
> > >  static ssize_t iio_show_scan_index(struct device *dev,
> > >                                  struct device_attribute *attr,
> > >                                  char *buf)
> > > @@ -1453,9 +1467,11 @@ static void __iio_buffer_free_sysfs_and_mask(struct iio_buffer *buffer)
> > >
> > >  int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
> > >  {
> > > -     struct iio_buffer *buffer = indio_dev->buffer;
> > > +     struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > >       const struct iio_chan_spec *channels;
> > > -     int i;
> > > +     struct iio_buffer *buffer;
> > > +     int unwind_idx;
> > > +     int ret, i;
> > >
> > >       channels = indio_dev->channels;
> > >       if (channels) {
> > > @@ -1466,22 +1482,46 @@ int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
> > >               indio_dev->masklength = ml;
> > >       }
> > >
> > > -     if (!buffer)
> > > +     if (!iio_dev_opaque->attached_buffers_cnt)
> > >               return 0;
> > >
> > > -     return __iio_buffer_alloc_sysfs_and_mask(buffer, indio_dev, 0);
> > > +     for (i = 0; i < iio_dev_opaque->attached_buffers_cnt; i++) {
> > > +             buffer = iio_dev_opaque->attached_buffers[i];
> > > +             ret = __iio_buffer_alloc_sysfs_and_mask(buffer, indio_dev, i);
> > > +             if (ret) {
> > > +                     unwind_idx = i;
> > > +                     goto error_unwind_sysfs_and_mask;
> > > +             }
> > > +     }
> > > +
> > > +     return 0;
> > > +
> > > +error_unwind_sysfs_and_mask:
> > > +     for (; unwind_idx >= 0; unwind_idx--) {
> > > +             buffer = iio_dev_opaque->attached_buffers[unwind_idx];
> > > +             __iio_buffer_free_sysfs_and_mask(buffer);
> > > +     }
> > > +     kfree(iio_dev_opaque->attached_buffers);
> > > +     return ret;
> > >  }
> > >
> > >  void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev)
> > >  {
> >
> > Perhaps we should do a follow up adjusting names to slightly better
> > reflect they are not handling multiple buffers.
> >
> > > -     struct iio_buffer *buffer = indio_dev->buffer;
> > > +     struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > > +     struct iio_buffer *buffer;
> > > +     int i;
> > >
> > > -     if (!buffer)
> > > +     if (!iio_dev_opaque->attached_buffers_cnt)
> > >               return;
> > >
> > >       iio_buffer_unregister_legacy_sysfs_groups(indio_dev);
> > >
> > > -     __iio_buffer_free_sysfs_and_mask(buffer);
> > > +     for (i = iio_dev_opaque->attached_buffers_cnt - 1; i >= 0; i--) {
> > > +             buffer = iio_dev_opaque->attached_buffers[i];
> > > +             __iio_buffer_free_sysfs_and_mask(buffer);
> > > +     }
> > > +
> > > +     kfree(iio_dev_opaque->attached_buffers);
> >
> > Hmm. This does feel like it's in slightly the wrong place, but
> > I'm not sure where it actually should be.
> >
> > Given this is the last element in the call sequence I guess it doesn't
> > makes sense to bring in another function just to tidy up this connection.
> >
> > >  }
> > >
> > >  /**
> > > @@ -1599,13 +1639,35 @@ EXPORT_SYMBOL_GPL(iio_buffer_put);
> > >   * @indio_dev: The device the buffer should be attached to
> > >   * @buffer: The buffer to attach to the device
> > >   *
> > > + * Return 0 if successful, negative if error.
> > > + *
> > >   * This function attaches a buffer to a IIO device. The buffer stays attached to
> > > - * the device until the device is freed. The function should only be called at
> > > - * most once per device.
> > > + * the device until the device is freed. For legacy reasons, the first attached
> > > + * buffer will also be assigned to 'indio_dev->buffer'.
> > >   */
> > > -void iio_device_attach_buffer(struct iio_dev *indio_dev,
> > > -                           struct iio_buffer *buffer)
> > > +int iio_device_attach_buffer(struct iio_dev *indio_dev,
> > > +                          struct iio_buffer *buffer)
> > >  {
> > > -     indio_dev->buffer = iio_buffer_get(buffer);
> > > +     struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
> > > +     struct iio_buffer **new, **old = iio_dev_opaque->attached_buffers;
> > > +     unsigned int cnt = iio_dev_opaque->attached_buffers_cnt;
> > > +
> > > +     cnt++;
> > > +
> > > +     new = krealloc(old, sizeof(*new) * cnt, GFP_KERNEL);
> > > +     if (!new)
> > > +             return -ENOMEM;
> > > +     iio_dev_opaque->attached_buffers = new;
> > > +
> > > +     buffer = iio_buffer_get(buffer);
> > > +
> > > +     /* first buffer is legacy; attach it to the IIO device directly */
> > > +     if (!indio_dev->buffer)
> > > +             indio_dev->buffer = buffer;
> > > +
> > > +     iio_dev_opaque->attached_buffers[cnt - 1] = buffer;
> > > +     iio_dev_opaque->attached_buffers_cnt = cnt;
> > > +
> > > +     return 0;
> > >  }
> > >  EXPORT_SYMBOL_GPL(iio_device_attach_buffer);
> > > diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> > > index 1be94df3e591..26b05dddfa71 100644
> > > --- a/drivers/iio/industrialio-core.c
> > > +++ b/drivers/iio/industrialio-core.c
> > > @@ -1583,7 +1583,7 @@ static void iio_dev_release(struct device *device)
> > >       iio_device_unregister_eventset(indio_dev);
> > >       iio_device_unregister_sysfs(indio_dev);
> > >
> > > -     iio_buffer_put(indio_dev->buffer);
> > > +     iio_buffers_put(indio_dev);
> > >
> > >       ida_simple_remove(&iio_ida, indio_dev->id);
> > >       kfree(iio_dev_opaque);
> > > @@ -1884,12 +1884,12 @@ int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
> > >               indio_dev->setup_ops == NULL)
> > >               indio_dev->setup_ops = &noop_ring_setup_ops;
> > >
> > > -     if (indio_dev->buffer)
> > > +     if (iio_dev_opaque->attached_buffers_cnt)
> > >               cdev_init(&indio_dev->chrdev, &iio_buffer_fileops);
> > >       else if (iio_dev_opaque->event_interface)
> > >               cdev_init(&indio_dev->chrdev, &iio_event_fileops);
> > >
> > > -     if (indio_dev->buffer || iio_dev_opaque->event_interface) {
> > > +     if (iio_dev_opaque->attached_buffers_cnt || iio_dev_opaque->event_interface) {
> > >               indio_dev->dev.devt = MKDEV(MAJOR(iio_devt), indio_dev->id);
> > >               indio_dev->chrdev.owner = this_mod;
> > >       }
> > > diff --git a/include/linux/iio/buffer.h b/include/linux/iio/buffer.h
> > > index 8febc23f5f26..b6928ac5c63d 100644
> > > --- a/include/linux/iio/buffer.h
> > > +++ b/include/linux/iio/buffer.h
> > > @@ -41,7 +41,7 @@ static inline int iio_push_to_buffers_with_timestamp(struct iio_dev *indio_dev,
> > >  bool iio_validate_scan_mask_onehot(struct iio_dev *indio_dev,
> > >                                  const unsigned long *mask);
> > >
> > > -void iio_device_attach_buffer(struct iio_dev *indio_dev,
> > > -                           struct iio_buffer *buffer);
> > > +int iio_device_attach_buffer(struct iio_dev *indio_dev,
> > > +                          struct iio_buffer *buffer);
> > >
> > >  #endif /* _IIO_BUFFER_GENERIC_H_ */
> > > diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
> > > index 41044320e581..768b90c64412 100644
> > > --- a/include/linux/iio/buffer_impl.h
> > > +++ b/include/linux/iio/buffer_impl.h
> > > @@ -112,6 +112,9 @@ struct iio_buffer {
> > >       /* @demux_bounce: Buffer for doing gather from incoming scan. */
> > >       void *demux_bounce;
> > >
> > > +     /* @attached_entry: Entry in the devices list of buffers attached by the driver. */
> > > +     struct list_head attached_entry;
> > > +
> > >       /* @buffer_list: Entry in the devices list of current buffers. */
> > >       struct list_head buffer_list;
> > >
> > > diff --git a/include/linux/iio/iio-opaque.h b/include/linux/iio/iio-opaque.h
> > > index 3e4c3cd248fd..c909835b6247 100644
> > > --- a/include/linux/iio/iio-opaque.h
> > > +++ b/include/linux/iio/iio-opaque.h
> > > @@ -7,6 +7,8 @@
> > >   * struct iio_dev_opaque - industrial I/O device opaque information
> > >   * @indio_dev:                       public industrial I/O device information
> > >   * @event_interface:         event chrdevs associated with interrupt lines
> > > + * @attached_buffers:                array of buffers statically attached by the driver
> > > + * @attached_buffers_cnt:    number of buffers in the array of statically attached buffers
> > >   * @buffer_list:             list of all buffers currently attached
> > >   * @channel_attr_list:               keep track of automatically created channel
> > >   *                           attributes
> > > @@ -24,6 +26,8 @@
> > >  struct iio_dev_opaque {
> > >       struct iio_dev                  indio_dev;
> > >       struct iio_event_interface      *event_interface;
> > > +     struct iio_buffer               **attached_buffers;
> > > +     unsigned int                    attached_buffers_cnt;
> > >       struct list_head                buffer_list;
> > >       struct list_head                channel_attr_list;
> > >       struct attribute_group          chan_attr_group;
> >