Re: [PATCH 1/2] ads7846: Make buffers in struct ser_req and struct ads7845_ser_req DMA save

[Jonathan Cameron <jic23@cam.ac.uk>]

On 05/05/11 07:51, Alexander Stein wrote:
> req.sample needs its own cacheline otherwise accessing req.msg fetches
> it in again.
> 
> Note: This effect doesn't occur if the underlying SPI driver doesn't use
> DMA at all.
I would say the comment is a bit obvious, but then you are fixing a bug
because it was wrong - so fair call.
> 
> Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
> ---
> This obsoletes the patch
> [PATCH 1/2] ads7846: Make buffers in ads7846_read12_ser and ads7845_read12_ser DMA save
> 
>  drivers/input/touchscreen/ads7846.c |   12 ++++++++++--
>  1 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
> index c24946f..ab51a8d 100644
> --- a/drivers/input/touchscreen/ads7846.c
> +++ b/drivers/input/touchscreen/ads7846.c
> @@ -281,17 +281,25 @@ struct ser_req {
>  	u8			command;
>  	u8			ref_off;
>  	u16			scratch;
> -	__be16			sample;
>  	struct spi_message	msg;
>  	struct spi_transfer	xfer[6];
> +	/*
> +	 * DMA (thus cache coherency maintenance) requires the
> +	 * transfer buffers to live in their own cache lines.
> +	 */
> +	__be16 sample ____cacheline_aligned;
>  };
>  
>  struct ads7845_ser_req {
>  	u8			command[3];
>  	u8			pwrdown[3];
> -	u8			sample[3];
>  	struct spi_message	msg;
>  	struct spi_transfer	xfer[2];
> +	/*
> +	 * DMA (thus cache coherency maintenance) requires the
> +	 * transfer buffers to live in their own cache lines.
> +	 */
> +	u8 sample[3] ____cacheline_aligned;
>  };
>  
>  static int ads7846_read12_ser(struct device *dev, unsigned command)