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Subject[PATCH v3 10/10] dmaengine: dw: Initialize max_sg_nents with nollp flag
Multi-block support provides a way to map the kernel-specific SG-table so
the DW DMA device would handle it as a whole instead of handling the
SG-list items or so called LLP block items one by one. So if true LLP
list isn't supported by the DW DMA engine, then soft-LLP mode will be
utilized to load and execute each LLP-block one by one. The soft-LLP mode
of the DMA transactions execution might not work well for some DMA
consumers like SPI due to its Tx and Rx buffers inter-dependency. Let's
expose the nollp flag indicating the soft-LLP mode by means of the
max_sg_nents capability, so the DMA consumer would be ready to somehow
workaround errors caused by such mode being utilized.

Signed-off-by: Serge Semin <>
Cc: Alexey Malahov <>
Cc: Thomas Bogendoerfer <>
Cc: Arnd Bergmann <>
Cc: Rob Herring <>


Changelog v3:
- This is a new patch created as a result of the discussion with Vinud and
Andy in the framework of DW DMA burst and LLP capabilities.
drivers/dma/dw/core.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 29c4ef08311d..b850eb7fd084 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -1054,6 +1054,15 @@ static void dwc_caps(struct dma_chan *chan, struct dma_slave_caps *caps)
struct dw_dma_chan *dwc = to_dw_dma_chan(chan);

caps->max_burst = dwc->max_burst;
+ /*
+ * It might be crucial for some devices to have the hardware
+ * accelerated multi-block transfers supported, aka LLPs in DW DMAC
+ * notation. So if LLPs are supported then max_sg_nents is set to
+ * zero which means unlimited number of SG entries can be handled in a
+ * single DMA transaction, otherwise it's just one SG entry.
+ */
+ caps->max_sg_nents = dwc->nollp;

int do_dma_probe(struct dw_dma_chip *chip)
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