linux-kernel - Re: [PATCH 1/2 v2] dmaengine: rcar-dmac: ensure CHCR DE bit is actually 0 after clear

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Date:   Fri, 17 Nov 2017 09:41:05 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        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 1/2 v2] dmaengine: rcar-dmac: ensure CHCR DE bit is
 actually 0 after clear

Hi Morimoto-san,

On Fri, Nov 17, 2017 at 1:10 AM, Kuninori Morimoto
<kuninori.morimoto.gx@...esas.com> wrote:
>> > +static void rcar_dmac_chcr_de_barrier(struct rcar_dmac_chan *chan)
>> > +{
>> > +       u32 chcr;
>> > +       int i;
>>
>> unsigned int
>>
>> > +
>> > +       /*
>> > +        * Ensure that the setting of the DE bit is actually 0 after
>> > +        * clearing it.
>> > +        */
>> > +       for (i = 0; i < 1024; i++) {
>> > +               chcr = rcar_dmac_chan_read(chan, RCAR_DMACHCR);
>> > +               if (!(chcr & RCAR_DMACHCR_DE))
>> > +                       return;
>> > +               udelay(1);
>> > +       }
>>
>> What's a typical number of loops needed before DE is really cleared?
>
> It case by case, but I don't want to use while(1) loop

I understand that, and I agree wholeheartedly with limiting the number
of cycles.

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