linux-kernel - Re: [PATCH] i2c: designware: deduce speed mode from device tree setting

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Date:	Wed, 20 Aug 2014 09:24:45 -0500
From:	atull <atull@...nsource.altera.com>
To:	Romain Baeriswyl <Romain.Baeriswyl@...lis.com>
CC:	Mark Rutland <mark.rutland@....com>, <wsa@...-dreams.de>,
	<baruch@...s.co.il>,
	mika westerberg <mika.westerberg@...ux.intel.com>,
	grant likely <grant.likely@...aro.org>, <robh+dt@...nel.org>,
	<skuribay@...ox.com>,
	rafael j wysocki <rafael.j.wysocki@...el.com>,
	<alan@...ux.intel.com>, <linux-i2c@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
	delicious quinoa <delicious.quinoa@...il.com>,
	<dinguyen@...nsource.altera.com>, <yvanderv@...nsource.altera.com>
Subject: Re: [PATCH] i2c: designware: deduce speed mode from device tree
 setting



On Wed, 20 Aug 2014, Romain Baeriswyl wrote:

> Hi,
> 
> With the patch "i2c designware add support of I2C standard mode" I already proposed:
> - I2C standard mode is selected with 100kHz clock frequency.
> - I2C fast mode is selected with 400kHy clock frequency.
> - EINVAL error is returned if clock frequency is not 100000 and not 400000.
> 
> but this patch seems not available yet.
> What about the other patch "i2c designware make SCL and SDA falling time configurable" ?
> 
> In i2c-designware_platdrv.c the flag DW_IC_CON_SPEED_xxx is well set
> depending on the mode:
> 
>   if (clk_freq == 100000)

Romain,

I'm really happy if your patches get accepted.  Can this be <= 100000?
It is really common to run I2C at a lower speed if you have some
board issues with the i2c bus.

Alan

>      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;
> 
> 
> So for me everything should be fine if there patches are applied.
> 
> Regards,
> 
> Romain
> 
> ----- Original Message -----
> From: "Mark Rutland" <mark.rutland@....com>
> To: atull@...nsource.altera.com
> Cc: wsa@...-dreams.de, baruch@...s.co.il, "mika westerberg" <mika.westerberg@...ux.intel.com>, "grant likely" <grant.likely@...aro.org>, robh+dt@...nel.org, skuribay@...ox.com, "Romain Baeriswyl" <Romain.Baeriswyl@...lis.com>, "rafael j wysocki" <rafael.j.wysocki@...el.com>, alan@...ux.intel.com, linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, "delicious quinoa" <delicious.quinoa@...il.com>, dinguyen@...nsource.altera.com, yvanderv@...nsource.altera.com
> Sent: Wednesday, August 20, 2014 11:22:57 AM
> Subject: Re: [PATCH] i2c: designware: deduce speed mode from device tree setting
> 
> On Tue, Aug 19, 2014 at 09:18:49PM +0100, atull@...nsource.altera.com wrote:
> > From: Alan Tull <atull@...nsource.altera.com>
> > 
> > Use the documented, but unimplemented "clock-frequency"
> > Device Tree setting as a guide on whether to set the speed
> > mode bits in DW_IC_CON to standard or fast i2c mode.
> > 
> > Previously, the driver was hardwired to fast mode.  Default
> > to fast mode if the "clock-frequency" property is not present
> > for backwards compatiblity.
> > 
> > Signed-off-by: Alan Tull <atull@...nsource.altera.com>
> > ---
> >  drivers/i2c/busses/i2c-designware-platdrv.c |   10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
> > index bc87733..18cd3d9 100644
> > --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> > +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> > @@ -122,7 +122,8 @@ static int dw_i2c_probe(struct platform_device *pdev)
> >  	struct dw_i2c_dev *dev;
> >  	struct i2c_adapter *adap;
> >  	struct resource *mem;
> > -	int irq, r;
> > +	int irq, r, ret, speed = DW_IC_CON_SPEED_FAST;
> > +	u32 bus_rate;
> >  
> >  	irq = platform_get_irq(pdev, 0);
> >  	if (irq < 0) {
> > @@ -167,6 +168,11 @@ 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);
> > +
> > +		ret = of_property_read_u32(pdev->dev.of_node,
> > +					   "clock-frequency", &bus_rate);
> > +		if (!ret && (bus_rate <= 100000))
> > +			speed = DW_IC_CON_SPEED_STD;
> 
> This looks a bit odd.
> 
> If the device only supports two particular speeds why do we accept any
> other speed in the clock-frequency property? Surely we should at least
> warn that something was off?
> 
> Thanks,
> Mark
> 
> >  	}
> >  
> >  	dev->functionality =
> > @@ -177,7 +183,7 @@ static int dw_i2c_probe(struct platform_device *pdev)
> >  		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;
> > +		DW_IC_CON_RESTART_EN | speed;
> >  
> >  	/* Try first if we can configure the device from ACPI */
> >  	r = dw_i2c_acpi_configure(pdev);
> > -- 
> > 1.7.9.5
> > 
> > --
> > To unsubscribe from this list: send the line "unsubscribe devicetree" in
> > the body of a message to majordomo@...r.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > 
> 
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