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?
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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