linux-kernel - Re: [PATCH 7/9] net: ethernet: ti: cpts: calc mult and shift from refclk freq

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Message-ID: <20160914142210.GE28592@localhost.localdomain>
Date:   Wed, 14 Sep 2016 16:22:11 +0200
From:   Richard Cochran <richardcochran@...il.com>
To:     Grygorii Strashko <grygorii.strashko@...com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Mugunthan V N <mugunthanvnm@...com>,
        Sekhar Nori <nsekhar@...com>, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, WingMan Kwok <w-kwok2@...com>
Subject: Re: [PATCH 7/9] net: ethernet: ti: cpts: calc mult and shift from
 refclk freq

On Wed, Sep 14, 2016 at 04:02:29PM +0300, Grygorii Strashko wrote:
> @@ -35,6 +33,8 @@ Optional properties:
>  			  For example in dra72x-evm, pcf gpio has to be
>  			  driven low so that cpsw slave 0 and phy data
>  			  lines are connected via mux.
> +- cpts_clock_mult	: Numerator to convert input clock ticks into nanoseconds
> +- cpts_clock_shift	: Denominator to convert input clock ticks into nanoseconds

You should explain to the reader how these will be calculated when the
properties are missing.

> diff --git a/drivers/net/ethernet/ti/cpts.c b/drivers/net/ethernet/ti/cpts.c
> index ff8bb85..8046a21 100644
> --- a/drivers/net/ethernet/ti/cpts.c
> +++ b/drivers/net/ethernet/ti/cpts.c
> @@ -418,18 +418,60 @@ void cpts_unregister(struct cpts *cpts)
>  	clk_disable(cpts->refclk);
>  }
>  
> +static void cpts_calc_mult_shift(struct cpts *cpts)
> +{
> +	u64 maxsec;
> +	u32 freq;
> +	u32 mult;
> +	u32 shift;
> +	u64 ns;
> +	u64 frac;

Why so many new lines?  This isn't good style.  Please combine
variables of the same type into one line and sort the lists
alphabetically.

> +	if (cpts->cc_mult || cpts->cc.shift)
> +		return;
> +
> +	freq = clk_get_rate(cpts->refclk);
> +
> +	/* Calc the maximum number of seconds which we can run before
> +	 * wrapping around.
> +	 */
> +	maxsec = cpts->cc.mask;
> +	do_div(maxsec, freq);
> +	if (!maxsec)
> +		maxsec = 1;
> +	else if (maxsec > 600 && cpts->cc.mask > UINT_MAX)
> +		maxsec = 600;
> +
> +	clocks_calc_mult_shift(&mult, &shift, freq, NSEC_PER_SEC, maxsec);
> +
> +	cpts->cc_mult = mult;
> +	cpts->cc.mult = mult;
> +	cpts->cc.shift = shift;
> +	/* Check calculations and inform if not precise */

Contrary to this comment, you are not making any kind of judgment
about whether the calculations are precise or not.

> +	frac = 0;
> +	ns = cyclecounter_cyc2ns(&cpts->cc, freq, cpts->cc.mask, &frac);
> +
> +	dev_info(cpts->dev,
> +		 "CPTS: ref_clk_freq:%u calc_mult:%u calc_shift:%u error:%lld nsec/sec\n",
> +		 freq, cpts->cc_mult, cpts->cc.shift, (ns - NSEC_PER_SEC));
> +}
> +

Thanks,
Richard