According to the DW APB DMAC data book the minimum burst transaction length is 1 and it's true for any version of the controller since isn't parametrised in the coreAssembler so can't be changed at the IP-core synthesis stage. The maximum burst transaction can vary from channel to channel and from controller to controller depending on a IP-core parameter the system engineer activated during the IP-core synthesis. Let's initialise both min_burst and max_burst members of the DMA controller descriptor with extreme values so the DMA clients could use them to properly optimize the DMA requests. The channels and controller-specific max_burst length initialization will be introduced by the follow-up patches. Signed-off-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Cc: Alexey Malahov <Alexey.Malahov@xxxxxxxxxxxxxxxxxxxx> Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Rob Herring <robh+dt@xxxxxxxxxx> Cc: linux-mips@xxxxxxxxxxxxxxx Cc: devicetree@xxxxxxxxxxxxxxx --- Changelog v4: - This is a new patch suggested by Andy. Changelog v5: - Introduce macro with extreme min and max burst length supported by the DW DMA controller. - Initialize max_burst length capability with extreme burst length supported by the DW DMAC IP-core. --- drivers/dma/dw/core.c | 2 ++ include/linux/platform_data/dma-dw.h | 2 ++ 2 files changed, 4 insertions(+) diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c index ceded21537e2..4887aa2fc73c 100644 --- a/drivers/dma/dw/core.c +++ b/drivers/dma/dw/core.c @@ -1229,6 +1229,8 @@ int do_dma_probe(struct dw_dma_chip *chip) dw->dma.device_issue_pending = dwc_issue_pending; /* DMA capabilities */ + dw->dma.min_burst = DW_DMA_MIN_BURST; + dw->dma.max_burst = DW_DMA_MAX_BURST; dw->dma.src_addr_widths = DW_DMA_BUSWIDTHS; dw->dma.dst_addr_widths = DW_DMA_BUSWIDTHS; dw->dma.directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV) | diff --git a/include/linux/platform_data/dma-dw.h b/include/linux/platform_data/dma-dw.h index f3eaf9ec00a1..369e41e9dcc9 100644 --- a/include/linux/platform_data/dma-dw.h +++ b/include/linux/platform_data/dma-dw.h @@ -12,6 +12,8 @@ #define DW_DMA_MAX_NR_MASTERS 4 #define DW_DMA_MAX_NR_CHANNELS 8 +#define DW_DMA_MIN_BURST 1 +#define DW_DMA_MAX_BURST 256 /** * struct dw_dma_slave - Controller-specific information about a slave -- 2.26.2
