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SubjectRe: [PATCH v4 2/7] dmaengine: xilinx_dma: in axidma slave_sg and dma_cylic mode align split descriptors
On 02-08-18, 16:10, Andrea Merello wrote:

s/cylic/cyclic in patch title

> Whenever a single or cyclic transaction is prepared, the driver
> could eventually split it over several SG descriptors in order
> to deal with the HW maximum transfer length.
>
> This could end up in DMA operations starting from a misaligned
> address. This seems fatal for the HW if DRE is not enabled.

DRE?

>
> This patch eventually adjusts the transfer size in order to make sure
> all operations start from an aligned address.
>
> Cc: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
> Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
> Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
> ---
> Changes in v2:
> - don't introduce copy_mask field, rather rely on already-esistent
> copy_align field. Suggested by Radhey Shyam Pandey
> - reword title
> Changes in v3:
> - fix bug introduced in v2: wrong copy size when DRE is enabled
> - use implementation suggested by Radhey Shyam Pandey
> Changes in v4:
> - rework on the top of 1/6
> ---
> drivers/dma/xilinx/xilinx_dma.c | 22 ++++++++++++++++++----
> 1 file changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index a3aaa0e34cc7..aaa6de8a70e4 100644
> --- a/drivers/dma/xilinx/xilinx_dma.c
> +++ b/drivers/dma/xilinx/xilinx_dma.c
> @@ -954,15 +954,28 @@ static int xilinx_dma_alloc_chan_resources(struct dma_chan *dchan)
>
> /**
> * xilinx_dma_calc_copysize - Calculate the amount of data to copy
> + * @chan: Driver specific DMA channel
> * @size: Total data that needs to be copied
> * @done: Amount of data that has been already copied
> *
> * Return: Amount of data that has to be copied
> */
> -static int xilinx_dma_calc_copysize(int size, int done)
> +static int xilinx_dma_calc_copysize(struct xilinx_dma_chan *chan,
> + int size, int done)

please align with opening brace

> {
> - return min_t(size_t, size - done,
> + size_t copy = min_t(size_t, size - done,
> XILINX_DMA_MAX_TRANS_LEN);
> +
> + if ((copy + done < size) &&
> + chan->xdev->common.copy_align) {
> + /*
> + * If this is not the last descriptor, make sure
> + * the next one will be properly aligned
> + */
> + copy = rounddown(copy,
> + (1 << chan->xdev->common.copy_align));
> + }
> + return copy;
> }
>
> /**
> @@ -1804,7 +1817,7 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_slave_sg(
> * Calculate the maximum number of bytes to transfer,
> * making sure it is less than the hw limit
> */
> - copy = xilinx_dma_calc_copysize(sg_dma_len(sg),
> + copy = xilinx_dma_calc_copysize(chan, sg_dma_len(sg),
> sg_used);
> hw = &segment->hw;
>
> @@ -1909,7 +1922,8 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_dma_cyclic(
> * Calculate the maximum number of bytes to transfer,
> * making sure it is less than the hw limit
> */
> - copy = xilinx_dma_calc_copysize(period_len, sg_used);
> + copy = xilinx_dma_calc_copysize(chan,
> + period_len, sg_used);
> hw = &segment->hw;
> xilinx_axidma_buf(chan, hw, buf_addr, sg_used,
> period_len * i);
> --
> 2.17.1

--
~Vinod

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