On Thu, Jul 30, 2020 at 06:45:43PM +0300, Serge Semin wrote: > Indeed in case of the DMA_DEV_TO_MEM DMA transfers it's enough to take the > destination memory address and the destination master data width into > account to calculate the CTLx.DST_TR_WIDTH setting of the memory > peripheral. According to the DW DMAC IP-core Databook (page 66, Example 5) Always put a version of the Databook document. I have several and they may differ. > at the and of a DMA transfer when the DMA-channel internal FIFO is left > with data less than for a single destination burst transaction, the > destination peripheral will enter the Single Transaction Region where the > DW DMA controller can complete a block transfer to the destination using > single transactions (non-burst transaction of CTLx.DST_TR_WIDTH bytes). If > there is no enough data in the DMA-channel internal FIFO for even a single > non-burst transaction of CTLx.DST_TR_WIDTH bytes, then the channel enters > "FIFO flush mode". That mode is activated to empty the FIFO and flush the > leftovers out to the memory peripheral. The flushing procedure is simple. > The data is sent to the memory by means of a set of single transaction of > CTLx.SRC_TR_WIDTH bytes. To sum up it's redundant to use the LLPs length > to find out the CTLx.DST_TR_WIDTH parameter value, since each DMA transfer > will be completed with the CTLx.SRC_TR_WIDTH bytes transaction if it is > required. > In this commit we remove the LLP entry length from the statement which "In this commit" should be removed, see Submitting Patches ("This patch"). > calculates the memory peripheral DMA transaction width since it's > redundant due to the feature described above. By doing so we'll improve > the memory bus utilization and speed up the DMA-channel performance for > DMA_DEV_TO_MEM DMA-transfers. Okay, I have no objections. Acked-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > Signed-off-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> > --- > drivers/dma/dw/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c > index 4700f2e87a62..3da0aea9fe25 100644 > --- a/drivers/dma/dw/core.c > +++ b/drivers/dma/dw/core.c > @@ -723,7 +723,7 @@ dwc_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl, > lli_write(desc, sar, reg); > lli_write(desc, dar, mem); > lli_write(desc, ctlhi, ctlhi); > - mem_width = __ffs(data_width | mem | dlen); > + mem_width = __ffs(data_width | mem); > lli_write(desc, ctllo, ctllo | DWC_CTLL_DST_WIDTH(mem_width)); > desc->len = dlen; > > -- > 2.27.0 > -- With Best Regards, Andy Shevchenko