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dmaengine: dw-axi-dmac: Allow client-chosen width

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For devices where transfer lengths are not known upfront, there is a
danger when the destination is wider than the source that partial words
can be lost at the end of a transfer. Ideally the controller would be
able to flush the residue, but it can't - it's not even possible to tell
that there is any.

Instead, allow the client driver to avoid the problem by setting a
smaller width.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>
This commit is contained in:
Phil Elwell
2024-09-19 18:05:00 +01:00
committed by Dom Cobley
parent 5fe7161e7c
commit f5b17dcd65
1 changed files with 12 additions and 0 deletions
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12
drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
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@@ -771,6 +771,18 @@ static int dw_axi_dma_set_hw_desc(struct axi_dma_chan *chan,
case DMA_DEV_TO_MEM:
reg_burst_msize = axi_dma_encode_msize(chan->config.src_maxburst);
reg_width = __ffs(chan->config.src_addr_width);
/*
* For devices where transfer lengths are not known upfront,
* there is a danger when the destination is wider than the
* source that partial words can be lost at the end of a transfer.
* Ideally the controller would be able to flush the residue, but
* it can't - it's not even possible to tell that there is any.
* Instead, allow the client driver to avoid the problem by setting
* a smaller width.
*/
if (chan->config.dst_addr_width &&
(chan->config.dst_addr_width < mem_width))
mem_width = chan->config.dst_addr_width;
device_addr = phys_to_dma(chan->chip->dev, chan->config.src_addr);
ctllo = reg_width << CH_CTL_L_SRC_WIDTH_POS |
mem_width << CH_CTL_L_DST_WIDTH_POS |