From 0f9d5f008e2f096b14ff1f218a870199dd5264f4 Mon Sep 17 00:00:00 2001 From: Serge Semin Date: Thu, 23 Jul 2020 03:58:48 +0300 Subject: 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 Reviewed-by: Andy Shevchenko Link: https://lore.kernel.org/r/20200723005848.31907-11-Sergey.Semin@baikalelectronics.ru Signed-off-by: Vinod Koul --- drivers/dma/dw/core.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'drivers/dma') diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c index 588b9bae827c..eb9175133034 100644 --- 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) -- cgit v1.2.3