linux-kernel - Re: [PATCH 0/3] dmaengine: Stear users towards dma_request_slave

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Message-ID: <CAMuHMdUYcSPoK8NOSdMzU_Jtg84aPMNKeGnacnF7=aidV4eqvw@mail.gmail.com>
Date:   Tue, 4 Feb 2020 09:01:55 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Vinod Koul <vkoul@...nel.org>,
        dmaengine <dmaengine@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH 0/3] dmaengine: Stear users towards dma_request_slave_chan()

Hi Peter,

On Tue, Feb 4, 2020 at 7:52 AM Peter Ujfalusi <peter.ujfalusi@...com> wrote:
> On 03/02/2020 22.34, Geert Uytterhoeven wrote:
> > On Mon, Feb 3, 2020 at 9:21 PM John Paul Adrian Glaubitz
> > <glaubitz@...sik.fu-berlin.de> wrote:
> >> On 2/3/20 2:32 PM, Geert Uytterhoeven wrote:
> >>> Both rspi and sh-msiof have users on legacy SH (i.e. without DT):
> >>
> >> FWIW, there is a patch set by Yoshinori Sato to add device tree support
> >> for classical SuperH hardware. It was never merged, unfortunately :(.
> >
> > True.
> >
> >>> Anyone who cares for DMA on SuperH?
> >>
> >> What is DMA used for on SuperH? Wouldn't dropping it cut support for
> >> essential hardware features?
> >
> > It may make a few things slower.
>
> I would not drop DMA support but I would suggest to add dma_slave_map
> for non DT boot so the _compat() can be dropped.

Which is similar in spirit to gpiod_lookup and clk_register_clkdev(),
right?

> Imho on lower spec SoC (and I believe SuperH is) the DMA makes big
> difference offloading data movement from the CPU.

Assumed it is actually used...

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