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

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Date:   Mon, 16 Oct 2017 09:14:50 +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 9:12 AM, Kuninori Morimoto
<kuninori.morimoto.gx@...esas.com> wrote:
>> > 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>
> (snip)
>> However, shouldn't the register to use depend on the DMA direction?
>
> I think TCRB is OK for all direction,
> but yes, we can care its direction.
> I can post v2 patch, if you want.
> Geert do you want to care direction ?

Please do. I think in general the .get_residue() callback should return the
correct value for both reading and writing.

Thanks!

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