linux-kernel - Re: [PATCH 1/3] i2c: add DMA support for freescale i2c driver

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Message-Id: <201402280957.28985.marex@denx.de>
Date:	Fri, 28 Feb 2014 09:57:28 +0100
From:	Marek Vasut <marex@...x.de>
To:	Shawn Guo <shawn.guo@...aro.org>
Cc:	mark.rutland@....com, wsa@...-dreams.de,
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Yuan Yao <yao.yuan@...escale.com>
Subject: Re: [PATCH 1/3] i2c: add DMA support for freescale i2c driver

On Friday, February 28, 2014 at 03:23:52 AM, Shawn Guo wrote:
> On Fri, Feb 28, 2014 at 10:13:02AM +0800, Shawn Guo wrote:
> > On Thu, Feb 27, 2014 at 09:39:35PM +0100, Marek Vasut wrote:
> > > > @@ -193,6 +216,7 @@ static const struct imx_i2c_hwdata
> > > > imx1_i2c_hwdata  = {
> > > > 
> > > >  	.ndivs			= ARRAY_SIZE(imx_i2c_clk_div),
> > > >  	.i2sr_clr_opcode	= I2SR_CLR_OPCODE_W0C,
> > > >  	.i2cr_ien_opcode	= I2CR_IEN_OPCODE_1,
> > > > 
> > > > +	.has_dma_support	= false,
> > > > 
> > > >  };
> > > > 
> > > > @@ -203,6 +227,7 @@ static const struct imx_i2c_hwdata
> > > > imx21_i2c_hwdata  = { .ndivs			= 
ARRAY_SIZE(imx_i2c_clk_div),
> > > > 
> > > >  	.i2sr_clr_opcode	= I2SR_CLR_OPCODE_W0C,
> > > >  	.i2cr_ien_opcode	= I2CR_IEN_OPCODE_1,
> > > > 
> > > > +	.has_dma_support	= false,
> > > > 
> > > >  };
> > > > 
> > > > @@ -213,6 +238,7 @@ static struct imx_i2c_hwdata vf610_i2c_hwdata = {
> > > > 
> > > >  	.ndivs			= ARRAY_SIZE(vf610_i2c_clk_div),
> > > >  	.i2sr_clr_opcode	= I2SR_CLR_OPCODE_W1C,
> > > >  	.i2cr_ien_opcode	= I2CR_IEN_OPCODE_0,
> > > > 
> > > > +	.has_dma_support	= true,
> > > 
> > > So why exactly don't we have a DT prop for determining whether the
> > > controller has DMA support ?
> > 
> > Using DMA or PIO is a decision that should be made by driver on its own,
> > not device tree.
> 
> Sorry.  I misunderstood it.  Yes, we can look at the DT property 'dmas'
> to know if the controller has DMA capability.

You're right. Whether or not does the hardware support DMA transfers is a 
property of the hardware, that's why it should be in DT.

Best regards,
Marek Vasut
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