Hi Ulrich-san, Thank you for your comment! > From: Ulrich Hecht, Sent: Tuesday, November 26, 2019 7:45 PM > > > On November 22, 2019 at 7:13 AM Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote: > > > > > > This patch can improve performance when a sd card transfer size > > is multiples of 32 like a sd memory card. However, this may > > disimprove performance when a sd card transfer size is not > > multiples of 32 because this patch uses PIO instead of SYS-DMAC. > > I have logged the DMA transfer sizes of a Marvell SD8897 WiFi/BT chip, and there transfers that are not multiples of 32 > are infrequent (every second or so) and small (184 bytes); all large transfers are multiples of 32. > > Would it be practical to switch the DMA bus width down if odd sizes are encountered, and back up again otherwise? I don't know why, but according to drivers/dma/sh/rcar-dmac.c, we should not configure the channel while using it. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/dma/sh/rcar-dmac.c?h=v5.4#n1245 The comment has been described on the first commit. But, since other drivers don't mention such a limitation, I think we can remove the comments somehow. Best regards, Yoshihiro Shimoda > CU > Uli
