linux-kernel - Re: [PATCH v2 2/5] iio: Add output buffer support

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Date:   Thu, 18 Feb 2021 13:42:40 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     <linux-kernel@...r.kernel.org>, <linux-iio@...r.kernel.org>,
        <lars@...afoo.de>, <Michael.Hennerich@...log.com>,
        <nuno.sa@...log.com>, <dragos.bogdan@...log.com>
Subject: Re: [PATCH v2 2/5] iio: Add output buffer support

On Wed, 17 Feb 2021 10:34:35 +0200
Alexandru Ardelean <alexandru.ardelean@...log.com> wrote:

> From: Lars-Peter Clausen <lars@...afoo.de>
> 
> Currently IIO only supports buffer mode for capture devices like ADCs. Add
> support for buffered mode for output devices like DACs.
> 
> The output buffer implementation is analogous to the input buffer
> implementation. Instead of using read() to get data from the buffer write()
> is used to copy data into the buffer.
> 
> poll() with POLLOUT will wakeup if there is space available for more or
> equal to the configured watermark of samples.
> 
> Drivers can remove data from a buffer using iio_buffer_remove_sample(), the
> function can e.g. called from a trigger handler to write the data to
> hardware.
> 
> A buffer can only be either a output buffer or an input, but not both. So,
> for a device that has an ADC and DAC path, this will mean 2 IIO buffers
> (one for each direction).
> 
> The direction of the buffer is decided by the new direction field of the
> iio_buffer struct and should be set after allocating and before registering
> it.
> 
> Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>

Just one question on this, otherwise looks good to me.

Jonathan

> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 5d641f8adfbd..b9970c68005d 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -162,6 +162,69 @@ static ssize_t iio_buffer_read(struct file *filp, char __user *buf,
>  	return ret;
>  }
>  
...

>  /**
>   * iio_buffer_poll() - poll the buffer to find out if it has data
>   * @filp:	File structure pointer for device access
> @@ -182,8 +245,19 @@ static __poll_t iio_buffer_poll(struct file *filp,
>  		return 0;
>  
>  	poll_wait(filp, &rb->pollq, wait);
> -	if (iio_buffer_ready(indio_dev, rb, rb->watermark, 0))
> -		return EPOLLIN | EPOLLRDNORM;
> +
> +	switch (rb->direction) {
> +	case IIO_BUFFER_DIRECTION_IN:
> +		if (iio_buffer_ready(indio_dev, rb, rb->watermark, 0))
> +			return EPOLLIN | EPOLLRDNORM;
> +		break;
> +	case IIO_BUFFER_DIRECTION_OUT:
> +		if (iio_buffer_space_available(rb) >= rb->watermark)
> +			return EPOLLOUT | EPOLLWRNORM;
> +		break;
> +	}
> +
> +	/* need a way of knowing if there may be enough data... */

Curious on what this comment is referring to?

>  	return 0;
>  }
>  
> @@ -232,6 +306,16 @@ void iio_buffer_wakeup_poll(struct iio_dev *indio_dev)
>  	}
>  }
...