linux-kernel - Re: [PATCH] dmaengine: rcar-dmac: use DMATCRB when xxx_TO

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Message-ID: <20662392.QIFALme4hY@avalon>
Date:   Tue, 17 Oct 2017 14:55:06 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Vinod Koul <vinod.koul@...el.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>, 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: use DMATCRB when xxx_TO_MEM direction

Hi Morimoto-san,

On Tuesday, 17 October 2017 03:18:49 EEST Kuninori Morimoto wrote:
> Hi
> 
> > Thank you for your explanation.
> > My 1st patch focused to "transfer completed" count (= TCRB) for all case.
> > In any case, "completed" information should be used.
> > But in MEM_TO_DEV case, I thought if is OK if data was read from MEM
> > (= the data will be send to DEV automatically, I didn't care about
> > interruption) But yes, your opinion is correct I think.
> > 
> > I think MEM_TO_MEM should use TCRB.
> > I think logic is same as your MEM_TO_DEV explanation ?

TCRB is better for MEM_TO_MEM too in my opinion. When reporting residue 
information we should indicate how much data has been transferred, and that 
includes both read from source and written to destination.

> > Anyway, in all case I can use TCRB in v3 patch,
> > and it needs abouve explanation.
> 
> If so, I think v1 is enough... ?
> "transfer completed count is important for all case" is no doubt... ?

That's correct, but I don't think the explanation was detailed and clear 
enough. If it was Geert wouldn't have asked for a v2, and you wouldn't have 
agreed to his request :-)

-- 
Regards,

Laurent Pinchart