linux-kernel - Re: [PATCH] dmaengine: rcar-dmac: read DMATCRB instead of DMATCR for residue

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Date:   Mon, 16 Oct 2017 08:50:08 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Vinod Koul <vinod.koul@...el.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        dmaengine@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@...esas.com>
Subject: Re: [PATCH] dmaengine: rcar-dmac: read DMATCRB instead of DMATCR for residue

Hi Morimoto-san,

On Mon, Oct 16, 2017 at 7:28 AM, Kuninori Morimoto
<kuninori.morimoto.gx@...esas.com> wrote:
> From: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
>
> SYS/RT/Audio DMAC have both TCR/TCRB register.
> Its difference is transfer counter value of read (= TCR)
> or write (= TCRB). The relationship is like below.
>
>          TCR       TCRB
>  [SOURCE] -> [DMAC] -> [DESTINATION]
>
> Thus, we want to read TCRB instead of TCR for residue.
> Otherwise, Sound Capture has noise after PluseAudio support
> (= 07b7acb51d2 ("ASoC: rsnd: update pointer more accurate"))
>
> Signed-off-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@...esas.com>
> [Kuninori: added detail information in log]
> Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>

Thanks for your patch!

> --- a/drivers/dma/sh/rcar-dmac.c
> +++ b/drivers/dma/sh/rcar-dmac.c
> @@ -1310,7 +1310,7 @@ static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan,
>         }
>
>         /* Add the residue for the current chunk. */
> -       residue += rcar_dmac_chan_read(chan, RCAR_DMATCR) << desc->xfer_shift;
> +       residue += rcar_dmac_chan_read(chan, RCAR_DMATCRB) << desc->xfer_shift;

Indeed, TCR indicates the counter value used for reading, while TCRB indicates
the counter value used for writing.

However, shouldn't the register to use depend on the DMA direction?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds