linux-kernel - Re: [PATCH v3] dmaengine: rcar-dmac: use TCRB instead of TCR for residue

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Date:   Mon, 6 Nov 2017 01:24:33 +0000
From:   Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
To:     Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Cc:     Vinod Koul <vinod.koul@...el.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Dan Williams <dan.j.williams@...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>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v3] dmaengine: rcar-dmac: use TCRB instead of TCR for residue


Hi Geert

> Large serial console input (copy and pasting long lines) works, as that uses
> DMA. Small serial console input (typing) doesn't work.
>
> Apparently for the serial port, TCR contains the value we need (< 0x20),
> while TCRB always contains 0x20.
> Perhaps the code should use the minimum of both registers instead?

TCR(= read) happen 1st, and TCRB (= write) happen next.
"TCRB always contains 0x20" means, DMA didn't transfer data for some reason ?

"use minimum" idea can't guarantee data transfering, same as previous topic I guess.

Best regards
---
Kuninori Morimoto