linux-kernel - Re: [PATCH] i2c designware add support of I2C standard mode

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Date:	Wed, 20 Aug 2014 10:25:40 -0500
From:	atull <atull@...nsource.altera.com>
To:	Romain Baeriswyl <Romain.Baeriswyl@...lis.com>
CC:	Wolfram Sang <wsa@...-dreams.de>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Christian Ruppert <christian.ruppert@...lis.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Mark Rutland <mark.rutland@....com>, <baruch@...s.co.il>,
	<grant.likely@...aro.org>, <robh+dt@...nel.org>,
	<skuribay@...ox.com>, <alan@...ux.intel.com>,
	<devicetree@...r.kernel.org>, <delicious.quinoa@...il.com>,
	<dinguyen@...nsource.altera.com>, <yvanderv@...nsource.altera.com>,
	Romain Baeriswyl <romainba@...lis.com>
Subject: Re: [PATCH] i2c designware add support of I2C standard mode

On Wed, 20 Aug 2014, atull wrote:

> 
> 
> On Wed, 20 Aug 2014, Romain Baeriswyl wrote:
> 
> > From: Romain Baeriswyl <Romain.Baeriswyl@...lis.com>
> > 
> > Some legacy devices support ony I2C standard mode at 100kHz.
> > This patch allows to select the standard mode through the DTS
> > with the use of the existing clock-frequency parameter.
> > 
> > When clock-frequency parameter is not set, the fast mode is selected.
> > Only when the parameter is set at 100000, the standard mode is selected.
> > 
> > Signed-off-by: Romain Baeriswyl <romainba@...lis.com>
> > Reviewed-by: Christian Ruppert <christian.ruppert@...lis.com>
> > ---
> >  drivers/i2c/busses/i2c-designware-platdrv.c |   23 +++++++++++++++++++++--
> >  1 files changed, 21 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
> > index 402ec39..b543fe1 100644
> > --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> > +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> > @@ -122,6 +122,7 @@ static int dw_i2c_probe(struct platform_device *pdev)
> >  	struct i2c_adapter *adap;
> >  	struct resource *mem;
> >  	int irq, r;
> > +	u32 clk_freq;
> >  
> >  	irq = platform_get_irq(pdev, 0);
> >  	if (irq < 0) {
> > @@ -151,6 +152,9 @@ static int dw_i2c_probe(struct platform_device *pdev)
> >  		return PTR_ERR(dev->clk);
> >  	clk_prepare_enable(dev->clk);
> >  
> > +	/* fast mode by default because of legacy reasons */
> > +	clk_freq = 400000;
> > +
> >  	if (pdev->dev.of_node) {
> >  		u32 ht = 0;
> >  		u32 ic_clk = dev->get_clk_rate_khz(dev);
> > @@ -166,6 +170,17 @@ static int dw_i2c_probe(struct platform_device *pdev)
> >  		of_property_read_u32(pdev->dev.of_node,
> >  				     "i2c-scl-falling-time-ns",
> >  				     &dev->scl_falling_time);
> > +
> > +		of_property_read_u32(pdev->dev.of_node, "clock-frequency",
> > +				     &clk_freq);
> > +
> > +		/* Only standard mode at 100kHz and fast mode at 400kHz
> > +		 * are supported.
> > +		 */
> > +		if (clk_freq != 100000 && clk_freq != 400000) {
> > +			dev_err(&pdev->dev, "Only 100kHz and 400kHz supported");
> > +			return -EINVAL;
> > +		}
> 
> Hi Romain,
> 
> It is common to operate i2c at <100KHz on boards that have i2c 
> issues.  I am using this driver at 50KHz because I have a LCD module 
> that just doesn't work at a full 100KHz.  Please remove the check for 
> these two frequency points.
> 
> >  	}
> >  
> >  	dev->functionality =
> > @@ -175,8 +190,12 @@ static int dw_i2c_probe(struct platform_device *pdev)
> >  		I2C_FUNC_SMBUS_BYTE_DATA |
> >  		I2C_FUNC_SMBUS_WORD_DATA |
> >  		I2C_FUNC_SMBUS_I2C_BLOCK;
> > -	dev->master_cfg =  DW_IC_CON_MASTER | DW_IC_CON_SLAVE_DISABLE |
> > -		DW_IC_CON_RESTART_EN | DW_IC_CON_SPEED_FAST;
> > +	if (clk_freq == 100000)
> 
> Please change to <=
> 

Hi Romain,

This looks fine to me, my "<= issues" are not important as this isn't 
really setting a frequency, but just setting a bit that controls speed.

Acked-by: Alan Tull <atull@...nsource.altera.com>


> > +		dev->master_cfg =  DW_IC_CON_MASTER | DW_IC_CON_SLAVE_DISABLE |
> > +			DW_IC_CON_RESTART_EN | DW_IC_CON_SPEED_STD;
> > +	else
> > +		dev->master_cfg =  DW_IC_CON_MASTER | DW_IC_CON_SLAVE_DISABLE |
> > +			DW_IC_CON_RESTART_EN | DW_IC_CON_SPEED_FAST;
> >  
> >  	/* Try first if we can configure the device from ACPI */
> >  	r = dw_i2c_acpi_configure(pdev);
> > -- 
> > 1.7.1
> > 
> > 
> 
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