linux-kernel - Re: [PATCH 3/3] i2c: nomadik: Add Device Tree support to the Nomadik I2C driver

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Date:	Fri, 31 Aug 2012 13:04:15 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Wolfram Sang <w.sang@...gutronix.de>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	STEricsson_nomadik_linux@...t.st.com, linus.walleij@...ricsson.com,
	arnd@...db.de, linux-i2c@...r.kernel.org
Subject: Re: [PATCH 3/3] i2c: nomadik: Add Device Tree support to the Nomadik
 I2C driver

> Is there some dependency other than updating the dts files? If not, I'd
> like to pick up the patch via I2C.

There's no other dependency. Feel free to take them into your tree.

> > +static void nmk_i2c_of_probe(struct device_node *np,
> > +			struct nmk_i2c_controller *pdata)
> > +{
> > +	/* Provide the default configuration as a base. */
> > +	pdata = &u8500_i2c;
> 
> ?????? I wonder how that could work... have you tested the patch?

Wow, that's a great spot!

I have tested the patch, but I don't have any i2c devices, so can't
test full functionality. I, wrongly it seems, assumed there would be
a complaint from the I2C subsystem if any of the values seemed wrong.
What I will do before next submission is print out the entire pdata
structure to ensure it's populated in the correct way.

> > +
> > +	of_property_read_u32(np, "clock-frequency", (u32*)&pdata->clk_freq);
> 
> Might be worth changing clk_freq to u32?

Yes, makes sense. 

> > +
> > +	/* This driver only supports 'standard' and 'fast' modes of operation. */
> > +	if (pdata->clk_freq <= 100000)
> > +		pdata->sm = I2C_FREQ_MODE_STANDARD;
> 
> Is standard == 100000 Hz?

Well it depends on how you interpret the comments in:
     include/linux/platform_data/i2c-nomadik.h

enum i2c_freq_mode {
        I2C_FREQ_MODE_STANDARD,         /* up to 100 Kb/s */
        I2C_FREQ_MODE_FAST,             /* up to 400 Kb/s */
        I2C_FREQ_MODE_HIGH_SPEED,       /* up to 3.4 Mb/s */
        I2C_FREQ_MODE_FAST_PLUS,        /* up to 1 Mb/s */
};

I guess your guess would be better than mine.

> > +	else
> > +		pdata->sm = I2C_FREQ_MODE_FAST;
> 
> If those two are fixed frequencies, you should omit a warning if the
> devicetree has a different frequency set and report which one is going
> to be used actually.

Well, again by the comments above I would say that in between values
were valid, but I'm willing to bow down to your knowledge if you think
they are fixed values?

Thanks for reviewing.

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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