Message-ID: <20210205123915.000012dc@Huawei.com>
Date:   Fri, 5 Feb 2021 12:39:15 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Alexandru Ardelean <ardeleanalex@...il.com>
CC:     Alexandru Ardelean <alexandru.ardelean@...log.com>,
        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>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v3 08/11] iio: buffer: wrap all buffer attributes into
 iio_dev_attr

On Fri, 5 Feb 2021 11:17:04 +0200
Alexandru Ardelean <ardeleanalex@...il.com> wrote:

> On Thu, Feb 4, 2021 at 8:26 PM Jonathan Cameron
> <Jonathan.Cameron@...wei.com> wrote:
> >
> > On Mon, 1 Feb 2021 16:51:02 +0200
> > Alexandru Ardelean <alexandru.ardelean@...log.com> wrote:
> >  
> > > This change wraps all buffer attributes into iio_dev_attr objects, and
> > > assigns a reference to the IIO buffer they belong to.
> > >
> > > With the addition of multiple IIO buffers per one IIO device, we need a way
> > > to know which IIO buffer is being enabled/disabled/controlled.
> > >
> > > We know that all buffer attributes are device_attributes. So we can wrap
> > > them with a iio_dev_attr types. In the iio_dev_attr type, we can also hold
> > > a reference to an IIO buffer.
> > > So, we end up being able to allocate wrapped attributes for all buffer
> > > attributes (even the one from other drivers).
> > >
> > > The neat part with this mechanism, is that we don't need to add any extra
> > > cleanup, because these attributes are being added to a dynamic list that
> > > will get cleaned up via iio_free_chan_devattr_list().  
> >
> >  
> > >
> > > With this change, the 'buffer->scan_el_dev_attr_list' list is being renamed
> > > to 'buffer->buffer_attr_list', effectively merging (or finalizing the
> > > merge) of the buffer/ & scan_elements/ attributes internally.
> > >
> > > Accessing these new buffer attributes can now be done via
> > > 'to_iio_dev_attr(attr)->buffer' inside the show/store handlers.  
> >
> > That is going to look a bit odd in any drivers that use it given they
> > will appear to not be embedded.
> >
> > There seem to be very few such attributes from a quick grep, so maybe
> > we may want to unwind this and change all the types.   Might still need
> > to set .buffer for some of them though (only applying to new drivers as
> > clearly current ones don't care!)
> >
> > Looking at what they actually are, some perhaps shouldn't have been in the buffer
> > directory in the first place (with hindsight!).
> >
> > Anyhow, aside from that oddity this looks good to me.  
> 
> I'm a little vague here.
> If there is a suggestion for a change, I may have missed it.

It was vague because I wasn't sure if it it made sense :)
> 
> I'm a bit vague on the part of "we may want to unwind this and change
> all the types"
> Is it referring to something like this patch?
>       https://lore.kernel.org/linux-iio/20210122162529.84978-10-alexandru.ardelean@analog.com/

Exactly, that was what I was wondering about.

> We could do a show/store version that takes an iio_buf_attr or
> iio_dev_attr parameter.
> But maybe at a later point?
> I don't feel it adds much benefit over the current usage of
> buffer->attrs, because we need to kmalloc these iio_dev_attr anyways
> to store the reference to the iio_buffer.
> 
> I would have liked to get rid of these user/external buffer->attrs.
> That would have made things easier.
> 
> But, it looks like there are several drivers using them.
> I usually find them by grepping for iio_triggered_buffer_setup_ext
> It's only 5 drivers that provide these attributes.
> It used to be a bit easier to find them by grepping
> iio_buffer_set_attrs(), but I removed that.

We could look at whether some can be brought into the core.  They tend
to be around hwfifo parameters. Those could be specific to individual
buffers rather than device wide so at least some of them are correctly
placed in the buffer directory (I think - I've argued with myself about
this a few times in the past).

The only oddity we'll get from current approach is callbacks appearing
to access a container structure that they aren't associated with in the
driver.  Its the sort of interface that no one would ever realize was
possible.

Jonathan

> 
> 
> >
> > Jonathan
> >  
> > >
> > > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
> > > ---
> > >  drivers/iio/industrialio-buffer.c | 66 +++++++++++++++++++++----------
> > >  include/linux/iio/buffer_impl.h   |  4 +-
> > >  2 files changed, 48 insertions(+), 22 deletions(-)
> > >
> > > diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> > > index a525e88b302f..49996bed5f4c 100644
> > > --- a/drivers/iio/industrialio-buffer.c
> > > +++ b/drivers/iio/industrialio-buffer.c
> > > @@ -448,7 +448,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
> > >                                    IIO_SEPARATE,
> > >                                    &indio_dev->dev,
> > >                                    buffer,
> > > -                                  &buffer->scan_el_dev_attr_list);
> > > +                                  &buffer->buffer_attr_list);
> > >       if (ret)
> > >               return ret;
> > >       attrcount++;
> > > @@ -460,7 +460,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
> > >                                    0,
> > >                                    &indio_dev->dev,
> > >                                    buffer,
> > > -                                  &buffer->scan_el_dev_attr_list);
> > > +                                  &buffer->buffer_attr_list);
> > >       if (ret)
> > >               return ret;
> > >       attrcount++;
> > > @@ -473,7 +473,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
> > >                                            0,
> > >                                            &indio_dev->dev,
> > >                                            buffer,
> > > -                                          &buffer->scan_el_dev_attr_list);
> > > +                                          &buffer->buffer_attr_list);
> > >       else
> > >               ret = __iio_add_chan_devattr("en",
> > >                                            chan,
> > > @@ -483,7 +483,7 @@ static int iio_buffer_add_channel_sysfs(struct iio_dev *indio_dev,
> > >                                            0,
> > >                                            &indio_dev->dev,
> > >                                            buffer,
> > > -                                          &buffer->scan_el_dev_attr_list);
> > > +                                          &buffer->buffer_attr_list);
> > >       if (ret)
> > >               return ret;
> > >       attrcount++;
> > > @@ -495,8 +495,7 @@ static ssize_t iio_buffer_read_length(struct device *dev,
> > >                                     struct device_attribute *attr,
> > >                                     char *buf)
> > >  {
> > > -     struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -     struct iio_buffer *buffer = indio_dev->buffer;
> > > +     struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >
> > >       return sprintf(buf, "%d\n", buffer->length);
> > >  }
> > > @@ -506,7 +505,7 @@ static ssize_t iio_buffer_write_length(struct device *dev,
> > >                                      const char *buf, size_t len)
> > >  {
> > >       struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -     struct iio_buffer *buffer = indio_dev->buffer;
> > > +     struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >       unsigned int val;
> > >       int ret;
> > >
> > > @@ -538,8 +537,7 @@ static ssize_t iio_buffer_show_enable(struct device *dev,
> > >                                     struct device_attribute *attr,
> > >                                     char *buf)
> > >  {
> > > -     struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -     struct iio_buffer *buffer = indio_dev->buffer;
> > > +     struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >
> > >       return sprintf(buf, "%d\n", iio_buffer_is_active(buffer));
> > >  }
> > > @@ -1154,7 +1152,7 @@ static ssize_t iio_buffer_store_enable(struct device *dev,
> > >       int ret;
> > >       bool requested_state;
> > >       struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -     struct iio_buffer *buffer = indio_dev->buffer;
> > > +     struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >       bool inlist;
> > >
> > >       ret = strtobool(buf, &requested_state);
> > > @@ -1185,8 +1183,7 @@ static ssize_t iio_buffer_show_watermark(struct device *dev,
> > >                                        struct device_attribute *attr,
> > >                                        char *buf)
> > >  {
> > > -     struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -     struct iio_buffer *buffer = indio_dev->buffer;
> > > +     struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >
> > >       return sprintf(buf, "%u\n", buffer->watermark);
> > >  }
> > > @@ -1197,7 +1194,7 @@ static ssize_t iio_buffer_store_watermark(struct device *dev,
> > >                                         size_t len)
> > >  {
> > >       struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -     struct iio_buffer *buffer = indio_dev->buffer;
> > > +     struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >       unsigned int val;
> > >       int ret;
> > >
> > > @@ -1230,8 +1227,7 @@ static ssize_t iio_dma_show_data_available(struct device *dev,
> > >                                               struct device_attribute *attr,
> > >                                               char *buf)
> > >  {
> > > -     struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > -     struct iio_buffer *buffer = indio_dev->buffer;
> > > +     struct iio_buffer *buffer = to_iio_dev_attr(attr)->buffer;
> > >
> > >       return sprintf(buf, "%zu\n", iio_buffer_data_available(buffer));
> > >  }
> > > @@ -1256,6 +1252,26 @@ static struct attribute *iio_buffer_attrs[] = {
> > >       &dev_attr_data_available.attr,
> > >  };
> > >
> > > +#define to_dev_attr(_attr) container_of(_attr, struct device_attribute, attr)
> > > +
> > > +static struct attribute *iio_buffer_wrap_attr(struct iio_buffer *buffer,
> > > +                                           struct attribute *attr)
> > > +{
> > > +     struct device_attribute *dattr = to_dev_attr(attr);
> > > +     struct iio_dev_attr *iio_attr;
> > > +
> > > +     iio_attr = kzalloc(sizeof(*iio_attr), GFP_KERNEL);
> > > +     if (!iio_attr)
> > > +             return NULL;
> > > +
> > > +     iio_attr->buffer = buffer;
> > > +     memcpy(&iio_attr->dev_attr, dattr, sizeof(iio_attr->dev_attr));
> > > +
> > > +     list_add(&iio_attr->l, &buffer->buffer_attr_list);
> > > +
> > > +     return &iio_attr->dev_attr.attr;
> > > +}
> > > +
> > >  static int iio_buffer_register_legacy_sysfs_groups(struct iio_dev *indio_dev,
> > >                                                  struct attribute **buffer_attrs,
> > >                                                  int buffer_attrcount,
> > > @@ -1331,7 +1347,7 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
> > >       }
> > >
> > >       scan_el_attrcount = 0;
> > > -     INIT_LIST_HEAD(&buffer->scan_el_dev_attr_list);
> > > +     INIT_LIST_HEAD(&buffer->buffer_attr_list);
> > >       channels = indio_dev->channels;
> > >       if (channels) {
> > >               /* new magic */
> > > @@ -1378,9 +1394,19 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
> > >
> > >       buffer_attrcount += ARRAY_SIZE(iio_buffer_attrs);
> > >
> > > -     attrn = buffer_attrcount;
> > > +     for (i = 0; i < buffer_attrcount; i++) {
> > > +             struct attribute *wrapped;
> > > +
> > > +             wrapped = iio_buffer_wrap_attr(buffer, attr[i]);
> > > +             if (!wrapped) {
> > > +                     ret = -ENOMEM;
> > > +                     goto error_free_scan_mask;
> > > +             }
> > > +             attr[i] = wrapped;
> > > +     }
> > >
> > > -     list_for_each_entry(p, &buffer->scan_el_dev_attr_list, l)
> > > +     attrn = 0;
> > > +     list_for_each_entry(p, &buffer->buffer_attr_list, l)
> > >               attr[attrn++] = &p->dev_attr.attr;
> > >
> > >       buffer->buffer_group.name = kasprintf(GFP_KERNEL, "buffer%d", index);
> > > @@ -1412,7 +1438,7 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
> > >  error_free_scan_mask:
> > >       bitmap_free(buffer->scan_mask);
> > >  error_cleanup_dynamic:
> > > -     iio_free_chan_devattr_list(&buffer->scan_el_dev_attr_list);
> > > +     iio_free_chan_devattr_list(&buffer->buffer_attr_list);
> > >
> > >       return ret;
> > >  }
> > > @@ -1443,7 +1469,7 @@ static void __iio_buffer_free_sysfs_and_mask(struct iio_buffer *buffer)
> > >       bitmap_free(buffer->scan_mask);
> > >       kfree(buffer->buffer_group.name);
> > >       kfree(buffer->buffer_group.attrs);
> > > -     iio_free_chan_devattr_list(&buffer->scan_el_dev_attr_list);
> > > +     iio_free_chan_devattr_list(&buffer->buffer_attr_list);
> > >  }
> > >
> > >  void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev)
> > > diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
> > > index 3e555e58475b..41044320e581 100644
> > > --- a/include/linux/iio/buffer_impl.h
> > > +++ b/include/linux/iio/buffer_impl.h
> > > @@ -97,8 +97,8 @@ struct iio_buffer {
> > >       /* @scan_timestamp: Does the scan mode include a timestamp. */
> > >       bool scan_timestamp;
> > >
> > > -     /* @scan_el_dev_attr_list: List of scan element related attributes. */
> > > -     struct list_head scan_el_dev_attr_list;
> > > +     /* @buffer_attr_list: List of buffer attributes. */
> > > +     struct list_head buffer_attr_list;
> > >
> > >       /*
> > >        * @buffer_group: Attributes of the new buffer group.  
> >  

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