Re: [PATCH] iio:kfifo_buf Take advantage of the fixed record size used in IIO

[Lars-Peter Clausen <lars@metafoo.de>]

On 05/19/2012 01:14 PM, Jonathan Cameron wrote:
> By bypassing the standard macros for setting up the kfifo we can
> take advantage of the fixed record size implementation without
> having to have a type to pass in (from which the size of an element
> is normally established).
> 
> In IIO we have variable 'scans' as our records in which any element
> can be present or not.  They do not however vary when we are
> actually filling or reading from the buffer.  Thus we have a fixed
> record size whenever we are actually running.  As setup and tear
> down are not in the fast path we can take the overhead of reinitializing
> the kfifo every time.
> 
> This is an RFC as
> 
> a) I'm far from sure I got it right.
> b) There is probably a better way of doing it!
> 
> Signed-off-by: Jonathan Cameron <jic23@kernel.org>
> ---
> Note this is against current staging-next.
> 
> 
>  drivers/iio/kfifo_buf.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/kfifo_buf.c b/drivers/iio/kfifo_buf.c
> index 6bf9d05..74b1cb8 100644
> --- a/drivers/iio/kfifo_buf.c
> +++ b/drivers/iio/kfifo_buf.c
> @@ -22,7 +22,8 @@ static inline int __iio_allocate_kfifo(struct iio_kfifo *buf,
>  		return -EINVAL;
>  
>  	__iio_update_buffer(&buf->buffer, bytes_per_datum, length);
> -	return kfifo_alloc(&buf->kf, bytes_per_datum*length, GFP_KERNEL);
> +	return __kfifo_alloc((struct __kfifo *)&buf->kf, length,
> +			     bytes_per_datum, GFP_KERNEL);
>  }
>  
>  static int iio_request_update_kfifo(struct iio_buffer *r)
> @@ -94,7 +95,7 @@ static int iio_store_to_kfifo(struct iio_buffer *r,
>  {
>  	int ret;
>  	struct iio_kfifo *kf = iio_to_kfifo(r);
> -	ret = kfifo_in(&kf->kf, data, r->bytes_per_datum);
> +	ret = __kfifo_in((struct __kfifo *)&kf->kf, data, r->bytes_per_datum);

The last parameter has to be 1 now, since we want to store one record. And I
think we can still use kfifo_in(...), the macro magic take care of doing the
right thing.

>  	if (ret != r->bytes_per_datum)
>  		return -EBUSY;
>  	return 0;
> @@ -110,7 +111,7 @@ static int iio_read_first_n_kfifo(struct iio_buffer *r,
>  		return -EINVAL;
>  
>  	n = rounddown(n, r->bytes_per_datum);
> -	ret = kfifo_to_user(&kf->kf, buf, n, &copied);

Same here. n needs to be n / r->bytes_per_datum

> +	ret = __kfifo_to_user((struct __kfifo *)&kf->kf, buf, n, &copied);
>  
>  	return copied;
>  }