Message-ID: <20210206144632.4d55a55b@archlinux>
Date:   Sat, 6 Feb 2021 14:46:32 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Alexandru Ardelean <ardeleanalex@...il.com>
Cc:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        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>,
        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 14:57:29 +0200
Alexandru Ardelean <ardeleanalex@...il.com> wrote:

> On Fri, Feb 5, 2021 at 2:40 PM Jonathan Cameron
> <Jonathan.Cameron@...wei.com> wrote:
> >
> > 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.  
> 
> So, from a perspective of API for drivers, it would probably make
> sense to have those sort of store/show hook types.
> But I am leaning towards maybe moving the HW fifo stuff into IIO core somehow.
> Which would make these [new] store/show hooks unneeded [for now at least].

Agreed. It probably makes sense to look at pulling these into the core.
When we first did this I was a little unsure how common these would be
but now it's been a while we know they do occur on multiple devices
(even if not that many of them!)

> 
> >  
> > > 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).  
> 
> I think they could be brought into core.
> But they would take some time (because of testing)
> These HW Fifo attributes were copied around between drivers and ended
> being the same.
> So, some IIO core logic would make sense. It's 5 drivers now.

Agree entirely.  This is ready for some tidying up, but not a quick job
as you say because of testing so let us leave it for now.  (better
things to be doing :)

> 
> >
> > 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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