From: Maxime Ripard <maxime.ripard@free-electrons.com>
To: Michal Suchanek <hramrach@gmail.com>
Cc: Mark Brown <broonie@kernel.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
linux-sunxi <linux-sunxi@googlegroups.com>,
Chen-Yu Tsai <wens@csie.org>,
linux-spi <linux-spi@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 5/5] RFC spi: sun4i: add DMA support
Date: Thu, 2 Jun 2016 10:18:24 +0200 [thread overview]
Message-ID: <20160602081824.GH4908@lukather> (raw)
In-Reply-To: <CAOMqctSWnbUaOveMUhz+yOJqTOK4EhDd5jUqKoHCohfndNAjWA@mail.gmail.com>
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On Tue, May 31, 2016 at 04:19:28PM +0200, Michal Suchanek wrote:
> On 31 May 2016 at 15:27, Mark Brown <broonie@kernel.org> wrote:
> > On Tue, May 31, 2016 at 12:44:54PM +0200, Michal Suchanek wrote:
> >> On 30 May 2016 at 17:50, Mark Brown <broonie@kernel.org> wrote:
> >> > On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote:
> >
> >> >> It's what the driver did to start with and it was requested to fall
> >> >> back to non-DMA in the case DMA is not available.
> >
> >> > Why? I really can't see any sensible use case for this that doesn't
> >> > have a better solution available.
> >
> >> Of course, the solution is to compile in the DMA driver.
> >
> >> It's been argued that some drivers which use only short transfers will
> >> just work.
> >
> > With nothing else in the system that needs DMA? It's making the
> > performance of the system less reliable for the benefit of a very narrow
> > use case.
>
> Some of the platform devices have dedicated DMA *controller* built
> into the device IP so the DMA engine really is optional on many sunxi
> devices. Besides SPI you definitely need the DMA engine for audio. You
> probably don't need it for storage and graphics. I don't have any idea
> if it's used for USB and Ethernet.
USB and Ethernet have their own dedicated DMA engines. So currently,
the only driver that requires it is the audio codec.
Maxime
--
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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next prev parent reply other threads:[~2016-06-02 8:18 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1464130597.git.hramrach@gmail.com>
[not found] ` <e315008b5e9dc3f1490507508fd2f6e94767dfbb.1464130597.git.hramrach@gmail.com>
2016-05-30 8:37 ` [PATCH 2/5] spi: sun4i: fix FIFO limit Maxime Ripard
[not found] ` <5fffb7eca6f4b70853d92be2403595d6d06bede7.1464130597.git.hramrach@gmail.com>
2016-05-30 8:37 ` [PATCH 3/5] spi: sunxi: expose maximum transfer size limit Maxime Ripard
2016-05-30 8:57 ` Michal Suchanek
2016-06-01 18:14 ` Maxime Ripard
[not found] ` <7292b1fa08de4f453a643beb63e9faa7826726f6.1464130597.git.hramrach@gmail.com>
2016-05-30 9:17 ` [PATCH 4/5] spi: sunxi: set maximum and minimum speed of SPI master Maxime Ripard
[not found] ` <cb90b922caa6ac07c1425d726ea19709ee5284f4.1464130597.git.hramrach@gmail.com>
2016-05-27 2:05 ` [linux-sunxi] [PATCH 1/5] spi: sunxi: fix transfer timeout Julian Calaby
2016-05-27 5:05 ` Michal Suchanek
2016-05-27 5:10 ` Julian Calaby
2016-05-30 11:23 ` Mark Brown
2016-05-31 11:52 ` Michal Suchanek
2016-06-01 18:20 ` Maxime Ripard
2016-05-30 9:44 ` Maxime Ripard
[not found] ` <ba0d6eb37cc4b0d2c46acbf9fcd7d644b3545ce8.1464130597.git.hramrach@gmail.com>
2016-05-30 11:26 ` [PATCH 5/5] RFC spi: sun4i: add DMA support Mark Brown
2016-05-30 12:11 ` Geert Uytterhoeven
2016-05-30 15:03 ` Mark Brown
2016-05-30 15:28 ` Michal Suchanek
2016-05-30 15:50 ` Mark Brown
2016-05-31 10:44 ` Michal Suchanek
2016-05-31 13:27 ` Mark Brown
2016-05-31 14:19 ` Michal Suchanek
2016-06-02 8:18 ` Maxime Ripard [this message]
2016-06-01 18:00 ` Maxime Ripard
2016-06-02 4:42 ` [linux-sunxi] " Priit Laes
2016-06-02 9:18 ` Mark Brown
2016-06-02 12:14 ` Michal Suchanek
2016-06-02 14:26 ` Mark Brown
2016-06-05 11:27 ` Michal Suchanek
2016-06-06 11:36 ` Mark Brown
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