linux-kernel - Re: [PATCH v4 09/13] net: ethernet: ti: cpts: rework initialization/deinitialization

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Date:   Tue, 6 Dec 2016 14:40:37 +0100
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, devicetree@...r.kernel.org,
        Murali Karicheri <m-karicheri2@...com>,
        Wingman Kwok <w-kwok2@...com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v4 09/13] net: ethernet: ti: cpts: rework
 initialization/deinitialization

On Mon, Dec 05, 2016 at 02:05:21PM -0600, Grygorii Strashko wrote:
> @@ -372,34 +354,27 @@ void cpts_tx_timestamp(struct cpts *cpts, struct sk_buff *skb)
>  }
>  EXPORT_SYMBOL_GPL(cpts_tx_timestamp);
>  
> -int cpts_register(struct device *dev, struct cpts *cpts,
> -		  u32 mult, u32 shift)
> +int cpts_register(struct cpts *cpts)
>  {
>  	int err, i;
>  
> -	cpts->info = cpts_info;
> -	spin_lock_init(&cpts->lock);
> -
> -	cpts->cc.read = cpts_systim_read;
> -	cpts->cc.mask = CLOCKSOURCE_MASK(32);
> -	cpts->cc_mult = mult;
> -	cpts->cc.mult = mult;
> -	cpts->cc.shift = shift;
> -
>  	INIT_LIST_HEAD(&cpts->events);
>  	INIT_LIST_HEAD(&cpts->pool);
>  	for (i = 0; i < CPTS_MAX_EVENTS; i++)
>  		list_add(&cpts->pool_data[i].list, &cpts->pool);
>  
> -	cpts_clk_init(dev, cpts);
> +	clk_enable(cpts->refclk);
> +
>  	cpts_write32(cpts, CPTS_EN, control);
>  	cpts_write32(cpts, TS_PEND_EN, int_enable);
>  
> +	/* reinitialize cc.mult to original value as it can be modified
> +	 * by cpts_ptp_adjfreq().
> +	 */
> +	cpts->cc.mult = cpts->cc_mult;

This still isn't quite right.  First of all, you shouldn't clobber the
learned cc.mult value in cpts_register().  Presumably, if PTP had been
run on this port before, then the learned frequency is approximately
correct, and it should be left alone.

[ BTW, resetting the timecounter here makes no sense either.  Why
  reset the clock just because the interface goes down?  ]

Secondly, you have made the initialization order of these fields hard
to follow.  With the whole series applied:

probe()
	cpts_create()
		cpts_of_parse()
		{
			/* Set cc_mult but not cc.mult! */
			set cc_mult
			set cc.shift
		}
		cpts_calc_mult_shift()
		{
			/* Set them both. */
			cpts->cc_mult = mult;
			cpts->cc.mult = mult;
			cpts->cc.shift = shift;
		}
/* later on */
cpts_register()
	cpts->cc.mult = cpts->cc_mult;

There is no need for such complexity.  Simply set cc.mult in
cpts_create() _once_, immediately after the call to
cpts_calc_mult_shift().

You can remove the assignment from cpts_calc_mult_shift() and
cpts_register().

Thanks,
Richard