From: broonie@kernel.org (Mark Brown)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 1/2] spi: sun4i: add DMA support
Date: Thu, 17 Mar 2016 11:58:39 +0000 [thread overview]
Message-ID: <20160317115839.GG2566@sirena.org.uk> (raw)
In-Reply-To: <CAOMqctSoA5WxtBCUK0PoHTV9OBi_fw4mdqOw+Dc_1DB_jghqng@mail.gmail.com>
On Thu, Mar 17, 2016 at 12:54:08PM +0100, Michal Suchanek wrote:
> That's what the driver does. The discussion revolves around the fact
> that the driver does not attempt to work (even for very short
> transfers) when the DMA channels are not configured and just bails
> out. AFAICT the channels are always available when the system is
> properly configured and the dmaengine driver loaded.
The driver should tell the core about this constraint so the core can
split the transfers for it.
> Very few device drivers would work with 63byte transfers only and the
> code for manually driving the CS line in case the DMA engine fails to
> configure will necessarily go untested most of the time since most
> systems will have DMA configured properly.
A lot of devices will be perfectly happy with 63 byte transfers,
register accesses for example tend to be much smaller than that. The
manual /CS might be an issue but for most SoCs that is easily addressed
by driving the pin as a GPIO if there's an issue.
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next prev parent reply other threads:[~2016-03-17 11:58 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-26 5:56 [PATCH RESEND 0/2] spi: sun4i: add DMA support Priit Laes
2016-02-26 5:56 ` [PATCH 1/2] " Priit Laes
2016-02-26 12:25 ` Mark Brown
2016-02-26 12:51 ` Michal Suchanek
2016-03-06 21:42 ` Maxime Ripard
2016-03-10 9:01 ` Michal Suchanek
2016-03-17 7:27 ` Maxime Ripard
2016-03-17 10:58 ` Michal Suchanek
2016-03-17 11:43 ` Mark Brown
2016-03-17 11:54 ` Michal Suchanek
2016-03-17 11:58 ` Mark Brown [this message]
2016-03-18 20:23 ` Maxime Ripard
2016-03-18 20:33 ` Mark Brown
2016-02-26 5:56 ` [PATCH 2/2] ARM: sunxi: spi: add notice about SPI FIFO limit Priit Laes
2016-03-06 18:12 ` Maxime Ripard
2016-02-26 12:15 ` [PATCH RESEND 0/2] spi: sun4i: add DMA support Mark Brown
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