linux-kernel - RE: [PATCH v2 1/2] i2c: add DMA support for freescale i2c driver

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Date:	Thu, 6 Mar 2014 04:36:14 +0000
From:	Yao Yuan <yao.yuan@...escale.com>
To:	Marek Vasut <marex@...x.de>
CC:	"wsa@...-dreams.de" <wsa@...-dreams.de>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: RE: [PATCH v2 1/2] i2c: add DMA support for freescale i2c driver

On Thu, March 06, 2014 at 11:23:50 AM, Marek Vasut wrote:
> On Wednesday, March 05, 2014 at 07:52:31 AM, Yuan Yao wrote:
> > Add dma support for i2c. This function depend on DMA driver.
> > You can turn on it by write both the dmas and dma-name properties in
> > dts node.
> >
> > Signed-off-by: Yuan Yao <yao.yuan@...escale.com>
> > ---
> 
> [...]
> 
> > @@ -601,6 +826,7 @@ static int i2c_imx_probe(struct platform_device
> *pdev)
> >  	void __iomem *base;
> >  	int irq, ret;
> >  	u32 bitrate;
> > +	u32 phy_addr;
> >
> >  	dev_dbg(&pdev->dev, "<%s>\n", __func__);
> >
> > @@ -611,6 +837,7 @@ static int i2c_imx_probe(struct platform_device
> *pdev)
> >  	}
> >
> >  	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +	phy_addr = res->start;
> 
> Uh ... Shawn, I really think I am lost here. Don't you need to map this
> memory before you can use it for DMA ? The DMA mapping function should
> give you the physical address and is the right way to go about this
> instead of pulling the address from here, no ?
> 
> I might be wrong here, I am rather uncertain, so please help me out.
> Thanks!

Hi, Marek, Thanks for your suggestion. 
Here you can review the code in include/linux/ioport.h
The resource->start describes the entity on the CPU bus as a starting physical address.
So I thinks it can used for dma directly.