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

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Date:	Wed, 20 Aug 2014 07:36:18 -0500
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Mark Rutland <mark.rutland@....com>
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

> > +
> > +		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.

> 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.

Thanks,

   Wolfram


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