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

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Date:   Tue, 4 Feb 2020 08:52:37 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
CC:     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 Geert, Adrian,

On 03/02/2020 22.34, Geert Uytterhoeven wrote:
> Hi Adrian,
> 
> 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.

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

> Does any of your SuperH boards use DMA?
> Anything interesting in /proc or /sys w.r.t. DMA?
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 

- Péter

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