[PATCH 3/8] spi: davinci: limit the transfer size if DMA enabled
Kevin Hilman
khilman at baylibre.com
Fri Feb 10 11:07:46 PST 2017
Frode Isaksen <fisaksen at baylibre.com> writes:
> Limit the transfer size to 20 scatter/gather pages if
> DMA is enabled.
> The eDMA DMA engine is limited to 20 SG entries in one DMA
> transaction. If this number is exceeded, DMA receive fails.
> This error occurs with large vmalloc'ed buffers.
>
> Signed-off-by: Frode Isaksen <fisaksen at baylibre.com>
> ---
> drivers/spi/spi-davinci.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/spi/spi-davinci.c b/drivers/spi/spi-davinci.c
> index b7b2da1..f1b46f6 100644
> --- a/drivers/spi/spi-davinci.c
> +++ b/drivers/spi/spi-davinci.c
> @@ -485,6 +485,16 @@ static bool davinci_spi_can_dma(struct spi_master *master,
> return __davinci_spi_can_dma(spi);
> }
>
> +static size_t davinci_spi_max_transfer_size(struct spi_device *spi)
> +{
> + /*
> + * The eDMA DMA engine is limited to 20 SG entries in one DMA
> + * transaction. If this number is exceeded, DMA receive fails.
> + * An extra SG entry is needed when the buffer is not page aligned.
> + */
> + return (__davinci_spi_can_dma(spi)) ? 19 * PAGE_SIZE : SIZE_MAX;
The number here should be a #define.
Also, comment says 20, code says 19. This should be clarified.
Kevin
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