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From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
To: Ulrich Hecht <uli@fpond.eu>
Cc: "linux-renesas-soc@vger.kernel.org"  <linux-renesas-soc@vger.kernel.org>
Subject: RE: [PATCH RFC 0/4] mmc: host: renesas_sdhi_sys_dmac: change dma_buswidth
Date: Mon, 2 Dec 2019 08:09:52 +0000	[thread overview]
Message-ID: <TYAPR01MB45446A5988FFD329A45C9A22D8430@TYAPR01MB4544.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <1619526348.1354132.1574765125512@webmail.strato.com>

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@renesas.com> 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

      reply	other threads:[~2019-12-02  8:09 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-22  6:13 [PATCH RFC 0/4] mmc: host: renesas_sdhi_sys_dmac: change dma_buswidth Yoshihiro Shimoda
2019-11-22  6:13 ` [PATCH RFC 1/4] mmc: host: renesas_sdhi_sys_dmac: Use dma_buswidth instead of hardcoded value Yoshihiro Shimoda
2019-11-26 10:45   ` Ulrich Hecht
2019-11-22  6:13 ` [PATCH RFC 2/4] mmc: host: renesas_sdhi_sys_dmac: Do not fall back to PIO Yoshihiro Shimoda
2019-11-26 10:45   ` Ulrich Hecht
2019-11-22  6:13 ` [PATCH RFC 3/4] mmc: host: renesas_sdhi_sys_dmac: add DMACR setting Yoshihiro Shimoda
2019-11-26 10:46   ` Ulrich Hecht
2019-12-02  8:19     ` Yoshihiro Shimoda
2019-11-22  6:13 ` [PATCH RFC 4/4] mmc: host: renesas_sdhi_sys_dmac: Set dma_buswidth value to 32 byte Yoshihiro Shimoda
2019-11-26 10:46   ` Ulrich Hecht
2019-11-28 21:07   ` Wolfram Sang
2019-12-02  8:38     ` Yoshihiro Shimoda
2019-12-02  8:54       ` Wolfram Sang
2019-11-26 10:45 ` [PATCH RFC 0/4] mmc: host: renesas_sdhi_sys_dmac: change dma_buswidth Ulrich Hecht
2019-12-02  8:09   ` Yoshihiro Shimoda [this message]

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