linux-kernel - Re: [PATCH] spi/pxa2xx-pci: Enable DMA binding through device name

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Date:	Thu, 24 Jul 2014 13:42:10 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Kweh Hock Leong <hock.leong.kweh@...el.com>,
	Eric Miao <eric.y.miao@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Chew Chiau Ee <chiau.ee.chew@...el.com>,
	Darren Hart <dvhart@...ux.intel.com>, chiauee85@...il.com,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH] spi/pxa2xx-pci: Enable DMA binding through device name

On Thursday 24 July 2014 18:01:51 Kweh Hock Leong wrote:
> From: "Chew, Chiau Ee" <chiau.ee.chew@...el.com>
> 
> Intel LPSS Baytrail supports two DMA controllers and SPI is only
> using one of the DMA controller. During DMA channel request,
> we need to ensure the requested Tx and Rx channels are from the correct
> DMA controller. Thus, we add extra checking in filter callback funtion
> by matching against the DMA controller device name.
> 
> Signed-off-by: Chew, Chiau Ee <chiau.ee.chew@...el.com>
> Signed-off-by: Kweh, Hock Leong <hock.leong.kweh@...el.com>

I'm confused. Doesn't  Bay Trail use ACPI to do the DMA
engine configuration? That should set find the right device/chan_id/slave_id
combination without any interaction, through the use of dma_request_slave_channel.

On a related note, there seems to be a bug in this driver, which
attempts to set the slave_id through dmaengine_slave_config(), which
is wrong in both cases, ACPI and filter functions.

	Arnd
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