Re: [PATCH v2 04/11] iio: add support for hardware fifo

[Hartmut Knaack <knaack.h@gmx.de>]

Octavian Purdila schrieb am 29.01.2015 um 12:38:
> On Thu, Jan 29, 2015 at 1:46 AM, Hartmut Knaack <knaack.h@gmx.de> wrote:
>>
>> Octavian Purdila schrieb am 21.12.2014 um 01:42:
>>> Some devices have hardware buffers that can store a number of samples
>>> for later consumption. Hardware usually provides interrupts to notify
>>> the processor when the fifo is full or when it has reached a certain
>>> threshold. This helps with reducing the number of interrupts to the
>>> host processor and thus it helps decreasing the power consumption.
>>>
>>> This patch adds support for hardware fifo to IIO by allowing the
>>> drivers to register operations for flushing the hadware fifo and
>>> setting the watermark level.
>>>
>>> A driver implementing hardware fifo support must also provide a
>>> watermark trigger which must contain "watermark" in its name.
>>>
>>
>> A few comments inline, also addressed to the other IIO maintainers.
>>
> 
> Thanks for the review Hartmut. What do you think about the watermark
> trigger approach?

Looks good to me, so far. But keep in mind, that I am still pretty new
to the IIO area, so people like Jonathan have a better understanding
where the core development started out and where it should be heading.
I will have a look at your other patches during the next days, as time
permits.

> 
> Also, after the discussion with Jonathan I am thinking of exposing a
> dedicated watermark level for the hardware FIFO. That way userspace
> can set a large value for the software buffer watermark and it also
> give control to userspace over the hardware watermark. I think that
> control is very important to achieve a good power/latency balance.
> 
>>> Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
>>> ---
>>>  Documentation/ABI/testing/sysfs-bus-iio | 22 +++++++++++++++++
>>>  drivers/iio/industrialio-buffer.c       | 44 ++++++++++++++++++++++++++++-----
>>>  include/linux/iio/iio.h                 | 17 +++++++++++++
>>>  3 files changed, 77 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
>>> index 7260f1f..6bb67ac 100644
>>> --- a/Documentation/ABI/testing/sysfs-bus-iio
>>> +++ b/Documentation/ABI/testing/sysfs-bus-iio
>>> @@ -1152,3 +1152,25 @@ Description:
>>>               Poll will block until the watermark is reached.
>>>               Blocking read will wait until the minimum between the requested
>>>               read amount or the low water mark is available.
>>> +             If the device has a hardware fifo this value is going to be used
>>> +             for the hardware fifo watermark as well.
>>> +
>>> +What:                /sys/bus/iio/devices/iio:deviceX/buffer/hwfifo-length
>>> +KernelVersion:       3.20
>>> +Contact:     linux-iio@vger.kernel.org
>>> +Description:
>>> +             A single positive integer specifying the maximum number of
>>> +             samples that the hardware fifo has. If the device does not
>>> +             support hardware fifo this is zero.
>>> +             When a device supports hardware fifo it will expose a trigger
>>> +             with the name that contains "watermark"
>>> +             (e.g. i2c-BMC150A:00-watermark-dev0).
>>> +             To use the hardware fifo the user must set an appropriate value
>>> +             in the buffer/length and buffer/low_watermark entries and select
>>> +             the watermark trigger. At that poin the hardware fifo will be
>>> +             enabled and the samples will be collected in a hardware buffer.
>>> +             When the number of samples in the hardware fifo reaches the
>>> +             watermark level the watermark trigger is issued and data is
>>> +             flushed to the devices buffer.
>>> +             A hardware buffer flush will also be triggered when reading from
>>> +             the device buffer and there is not enough data available.
>>> \ No newline at end of file
>>> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
>>> index 7f74c7f..3da6d07 100644
>>> --- a/drivers/iio/industrialio-buffer.c
>>> +++ b/drivers/iio/industrialio-buffer.c
>>> @@ -37,9 +37,17 @@ static bool iio_buffer_is_active(struct iio_buffer *buf)
>>>       return !list_empty(&buf->buffer_list);
>>>  }
>>>
>>> -static size_t iio_buffer_data_available(struct iio_buffer *buf)
>>> +static bool iio_buffer_data_available(struct iio_dev *indio_dev,
>>> +                                   struct iio_buffer *buf, size_t required)
>>>  {
>>> -     return buf->access->data_available(buf);
>>> +     size_t avail = buf->access->data_available(buf);
>>> +
>>> +     if (avail < required && indio_dev->hwfifo) {
>>> +             indio_dev->hwfifo->flush(indio_dev);
>>> +             avail = buf->access->data_available(buf);
>>> +     }
>>> +
>>> +     return avail >= required;
>>>  }
>>>
>>>  /**
>>> @@ -66,13 +74,13 @@ ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf,
>>>
>>>       do {
>>>               if (filp->f_flags & O_NONBLOCK) {
>>> -                     if (!iio_buffer_data_available(rb)) {
>>> +                     if (!iio_buffer_data_available(indio_dev, rb, 1)) {
>>>                               ret = -EAGAIN;
>>>                               break;
>>>                       }
>>>               } else {
>>>                       ret = wait_event_interruptible(rb->pollq,
>>> -                            iio_buffer_data_available(rb) >= to_read ||
>>> +                         iio_buffer_data_available(indio_dev, rb, to_read) ||
>>>                                                      indio_dev->info == NULL);
>>>                       if (ret)
>>>                               return ret;
>>> @@ -112,7 +120,7 @@ unsigned int iio_buffer_poll(struct file *filp,
>>>               return -ENODEV;
>>>
>>>       poll_wait(filp, &rb->pollq, wait);
>>> -     if (iio_buffer_data_available(rb) >= rb->low_watermark)
>>> +     if (iio_buffer_data_available(indio_dev, rb, rb->low_watermark))
>>>               return POLLIN | POLLRDNORM;
>>>       return 0;
>>>  }
>>> @@ -440,8 +448,14 @@ static ssize_t iio_buffer_write_length(struct device *dev,
>>>       if (buffer->length)
>>>               val = buffer->length;
>>>
>>> -     if (val < buffer->low_watermark)
>>> +     if (val < buffer->low_watermark) {
>>> +             if (indio_dev->hwfifo) {
>>> +                     ret = indio_dev->hwfifo->set_watermark(indio_dev, val);
>>> +                     if (ret)
>>> +                             return ret;
>>> +             }
>>>               buffer->low_watermark = val;
>>> +     }
>>>
>>>       return len;
>>>  }
>>> @@ -811,6 +825,12 @@ static ssize_t iio_buffer_store_watermark(struct device *dev,
>>>               goto out;
>>>       }
>>>
>>> +     if (indio_dev->hwfifo) {
>>> +             ret = indio_dev->hwfifo->set_watermark(indio_dev, val);
>>> +             if (ret)
>>> +                     goto out;
>>> +     }
>>> +
>>>       buffer->low_watermark = val;
>>>       ret = 0;
>>>  out:
>>> @@ -818,6 +838,16 @@ out:
>>>       return ret ? ret : len;
>>>  }
>>>
>>> +ssize_t iio_buffer_hwfifo_read_length(struct device *dev,
>>> +                                   struct device_attribute *attr,
>>> +                                   char *buf)
>>> +{
>>> +     struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>>> +     const struct iio_hwfifo *hwfifo = indio_dev->hwfifo;
>>> +
>>> +     return sprintf(buf, "%u\n", hwfifo ? hwfifo->length : 0);
>>> +}
>>> +
>>>  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,
>>> @@ -826,11 +856,13 @@ static DEVICE_ATTR(enable, S_IRUGO | S_IWUSR,
>>>                  iio_buffer_show_enable, iio_buffer_store_enable);
>>>  static DEVICE_ATTR(low_watermark, S_IRUGO | S_IWUSR,
>>>                  iio_buffer_show_watermark, iio_buffer_store_watermark);
>>> +static DEVICE_ATTR(hwfifo_length, S_IRUGO, iio_buffer_hwfifo_read_length, NULL);
>>>
>>>  static struct attribute *iio_buffer_attrs[] = {
>>>       &dev_attr_length.attr,
>>>       &dev_attr_enable.attr,
>>>       &dev_attr_low_watermark.attr,
>>> +     &dev_attr_hwfifo_length.attr,
>>>  };
>>>
>>>  int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
>>> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
>>> index 878d861..f64a05f 100644
>>> --- a/include/linux/iio/iio.h
>>> +++ b/include/linux/iio/iio.h
>>> @@ -417,6 +417,22 @@ struct iio_buffer_setup_ops {
>>>  };
>>>
>>>  /**
>>> + * struct iio_buffer_hwfifo_ops - hardware fifo operations
>>> + *
>>> + * @length:          [DRIVER] the hardware fifo length
>>> + * @set_watermark:   [DRIVER] setups the watermark level
>> Maybe use "sets" instead of "setups".
>>
> 
> Ok, sensible suggestion, I'll do that in the next version.
> 
>> Also, and this is more a general question, as it was quite annoying when getting into
>> the topic: I would prefer to place some information about the expected return values of
>> these functions into these descriptions. What do you guys think about that?
>>
>>> + * @flush:           [DRIVER] copies data from the hardware buffer to the
>>> + *                   device buffer
>>> + * @watermark_trig:  [DRIVER] an allocated and registered trigger containing
>>> + *                   "watermark" in its name
>>> + */
>>> +struct iio_hwfifo {
>>> +     int length;
>>> +     int (*set_watermark)(struct iio_dev *, unsigned int);
>>> +     int (*flush)(struct iio_dev *);
>>> +};
>>> +
>>> +/**
>>>   * struct iio_dev - industrial I/O device
>>>   * @id:                      [INTERN] used to identify device internally
>>>   * @modes:           [DRIVER] operating modes supported by device
>>> @@ -491,6 +507,7 @@ struct iio_dev {
>>>       int                             groupcounter;
>>>
>>>       unsigned long                   flags;
>>> +     const struct iio_hwfifo         *hwfifo;
>> This new entry should be added to the description of the iio_dev struct, as well.
> 
> Sure.
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