linux-kernel - Re: [PATCH v2] clk: si570: Add a driver for SI570 oscillators

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Message-ID: <1379546336.1787.95.camel@joe-AO722>
Date:	Wed, 18 Sep 2013 16:18:56 -0700
From:	Joe Perches <joe@...ches.com>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
Cc:	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Landley <rob@...dley.net>,
	Mike Turquette <mturquette@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Hyun Kwon <hyunk@...inx.com>
Subject: Re: [PATCH v2] clk: si570: Add a driver for SI570 oscillators

On Wed, 2013-09-18 at 16:09 -0700, Sören Brinkmann wrote:
> On Wed, Sep 18, 2013 at 04:02:41PM -0700, Joe Perches wrote:
> > On Wed, 2013-09-18 at 15:43 -0700, Soren Brinkmann wrote:
> > > Add a driver for SILabs 570, 571, 598, 599 programmable oscillators.
> > > The devices generate low-jitter clock signals and are reprogrammable via
> > > an I2C interface.
> > []
> > > v2:
> > []
> > >  - use 10000 as MIN and MAX value in usleep_range
> > []
> > > diff --git a/drivers/clk/clk-si570.c b/drivers/clk/clk-si570.c
> > []
> > > +static int si570_set_frequency(struct clk_si570 *data, unsigned long frequency)
> > > +{
> > []
> > > +	/* Applying a new frequency can take up to 10ms */
> > > +	usleep_range(10000, 10000);
> > 
> > Generally it's nicer to have an actual range for usleep_range.
> Well, as I said in the discussion with Guenther. I'm flexible and nobody
> objected when I said to make both equal. A real range doesn't make sense
> here though, but I don't know what's common practice for cases like
> this.

udelay is normal, but I guess you don't need atomic context.
 
> > Is there a bit you could periodically poll to see
> > if the new frequency has been set or is stable so
> > that a 10ms delay isn't always used?

> Unfortunately not.

Thanks.  I suppose I should read the datasheets before asking.

http://www.silabs.com/Support%20Documents/TechnicalDocs/si570.pdf
(page 12)

Anyway, perhaps si570_set_frequency_small needs a delay too.'

The 570 datasheet says it needs a 100uS delay.

> On Wed, 2013-09-18 at 15:43 -0700, Soren Brinkmann wrote:
> Add a driver for SILabs 570, 571, 598, 599 programmable oscillators.
> The devices generate low-jitter clock signals and are reprogrammable via
> an I2C interface.
> []
> +static int si570_set_frequency_small(struct clk_si570 *data,
> +				     unsigned long frequency)
> +{
> +	/*
> +	 * This is a re-implementation of DIV_ROUND_CLOSEST
> +	 * using the div64_u64 function lieu of letting the compiler
> +	 * insert EABI calls
> +	 */
> +	data->rfreq = div64_u64((data->rfreq * frequency) +
> +			div_u64(data->frequency, 2), data->frequency);
> +	regmap_write(data->regmap, SI570_REG_CONTROL, SI570_CNTRL_FREEZE_M);
> +	si570_update_rfreq(data);
> +	regmap_write(data->regmap, SI570_REG_CONTROL, 0);
> +
> +	return 0;
> +}


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