dmaengine: dw: Initialize max_sg_burst capability

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
initialize the max_sg_burst DMA channels capability based on the nollp
flag state. If it's true, no hardware accelerated LLP is available and
max_sg_burst should be set with 1, which means that the DMA engine
can handle only a single SG list entry at a time. If noLLP is set to
false, then hardware accelerated LLP is supported and the DMA engine
can handle infinite number of SG entries in a single DMA transaction.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200723005848.31907-11-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 588b9ba..eb91751 100644 (file)
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -1059,6 +1059,18 @@ 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_burst 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.
+        */
+       if (dwc->nollp)
+               caps->max_sg_burst = 1;
+       else
+               caps->max_sg_burst = 0;
 }
 
 int do_dma_probe(struct dw_dma_chip *chip)