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From: Geert Uytterhoeven <geert@linux-m68k.org>
To: linux-sh@vger.kernel.org
Subject: Re: Issues with rcar-dmac and sh-sci
Date: Sat, 15 Aug 2015 10:02:09 +0000	[thread overview]
Message-ID: <CAMuHMdV=nTCUVDJ71Jto0vbDesG2nUXHjbvbfHBwz6mksZ1U5Q@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1507162026200.821@ayla.of.borg>

On Sat, Aug 15, 2015 at 11:40 AM, Lars-Peter Clausen <lars@metafoo.de> wrote:
> On 08/15/2015 01:42 AM, Laurent Pinchart wrote:
>> On Thursday 16 July 2015 20:36:49 Geert Uytterhoeven wrote:
>>> While working on DMA for R-Car Gen2 using the sh-sci serial driver with
>>> rcar-dmac, I ran into two issues:
>>>
>>>   1. Unlike the old shdmac DMA engine driver, the new rcar-dmac DMA
>>>      engine driver does not support resubmitting a DMA descriptor.
>>>      I first tried the patch below, until I ran into the race condition,
>>>      after which I changed sh-sci to not reuse DMA descriptors.
>>
>> Is reusing descriptors something that the DMA engine API explicitly allows ?
>
> No. It explicitly forbids it. dmaengine_submit() must always be called in a
> pair with dmaenine_prep_*(). But there is some work in-progress to add

Thanks for the confirmation!
So the sh-sci driver violates the DMA engine API.

> support for re-usable descriptors, see
> http://www.spinics.net/lists/dmaengine/msg05554.html

Thanks, in the same thread:

   * DMA_CTRL_ACK
+    - If set, does not mean descriptor can be reused

http://www.spinics.net/lists/dmaengine/msg05552.html

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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

next prev parent reply	other threads:[~2015-08-15 10:02 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-16 18:36 Issues with rcar-dmac and sh-sci Geert Uytterhoeven
2015-08-14 23:42 ` Laurent Pinchart
2015-08-15  9:40 ` Lars-Peter Clausen
2015-08-15 10:02 ` Geert Uytterhoeven [this message]
2015-08-17 14:03 ` Geert Uytterhoeven
2015-08-18  6:35 ` Laurent Pinchart
2015-09-14 12:39 ` Hamza Farooq

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