linux-kernel - Re: [PATCH v7 2/3] I2C: mediatek: Add driver for MediaTek I2C controller

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Message-ID: <20150518063742.GA1545@katana>
Date:	Mon, 18 May 2015 08:37:42 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Eddie Huang <eddie.huang@...iatek.com>
Cc:	Sascha Hauer <kernel@...gutronix.de>, srv_heupstream@...iatek.com,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Xudong Chen <xudong.chen@...iatek.com>,
	Liguo Zhang <liguo.zhang@...iatek.com>,
	linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v7 2/3] I2C: mediatek: Add driver for MediaTek I2C
 controller

> > > +		rpaddr = dma_map_single(i2c->adap.dev.parent, msgs->buf,
> > > +						msgs->len, DMA_FROM_DEVICE);
> > 
> > I think you shouldn't use the adapter device here and later, but the dma
> > channel device.
> > 
> In MTK SoC, each I2C controller has its own DMA, and this DMA can't be
> used by other hardware.
> So I tend to use DMA directly, not through DMA channel.
> Even so, "i2c->adap.dev.parent" is not suitable here. I will change to
> use i2c->dev here. (Reference i2c-at91.c).

The better reference would be i2c-sh_mobile.c, especially commit
8cfcae9f0595bf0d145a67cfaa1051804a301d7c ("i2c: sh_mobile: use proper
device for mapping DMA memory") ;) The request to use the DMA channel
device came from the DMA folks, so if there is no real reason for an
exception, please use the channel device.


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