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

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Date:	Wed, 20 Aug 2014 13:42:31 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	"atull@...nsource.altera.com" <atull@...nsource.altera.com>,
	"baruch@...s.co.il" <baruch@...s.co.il>,
	"mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"skuribay@...ox.com" <skuribay@...ox.com>,
	"Romain.Baeriswyl@...lis.com" <Romain.Baeriswyl@...lis.com>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	"alan@...ux.intel.com" <alan@...ux.intel.com>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"delicious.quinoa@...il.com" <delicious.quinoa@...il.com>,
	"dinguyen@...nsource.altera.com" <dinguyen@...nsource.altera.com>,
	"yvanderv@...nsource.altera.com" <yvanderv@...nsource.altera.com>
Subject: Re: [PATCH] i2c: designware: deduce speed mode from device tree
 setting

On Wed, Aug 20, 2014 at 01:36:18PM +0100, Wolfram Sang wrote:
> > > +
> > > +		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?
> 
> "clock-frequency" is the default binding for specifying i2c bus speeds
> today. Some controllers can be programmed to do various speeds, some can
> only do a set of fixed values.

Sure. My complaint was that the driver would accept invalid values.
That wasn't meant to be suggestion to use a property other than the
standard clock-freqeuncy.

> > Surely we should at least warn that something was off?
> 
> Yes, I was going to say the same until Romain's old patch showed up
> which does that.

Cool. Sounds like we can use Romain's patch to handle this then.

Cheers,
Mark.
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