Octavian Purdila schrieb am 29.01.2015 um 12:38:
> On Thu, Jan 29, 2015 at 1:46 AM, Hartmut Knaack <knaack.h@xxxxxx> 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@xxxxxxxxx>
>>> ---
>>> 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@xxxxxxxxxxxxxxx
>>> +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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