linux-kernel - Re: [PATCH 14/15] twl4030_charger: Increase current carefully while watching voltage.

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Message-ID: <20150305175148.66453a33@notabene.brown>
Date:	Thu, 5 Mar 2015 17:51:48 +1100
From:	NeilBrown <neilb@...e.de>
To:	Pavel Machek <pavel@....cz>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>,
	Tony Lindgren <tony@...mide.com>,
	Lee Jones <lee.jones@...aro.org>,
	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	GTA04 owners <gta04-owner@...delico.com>,
	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH 14/15] twl4030_charger: Increase current carefully while
 watching voltage.

On Mon, 2 Mar 2015 22:29:45 +0100 Pavel Machek <pavel@....cz> wrote:

> On Tue 2015-02-24 15:33:53, NeilBrown wrote:
> > The USB Battery Charging spec (BC1.2) suggests a dedicated
> > charging port can deliver from 0.5 to 5.0A at between 4.75 and 5.25
> > volts.
> > 
> > To choose the "correct" current voltage setting requires a trial
> > and error approach: try to draw current and see if the voltage drops
> > too low.
> > 
> > Even with a configure Standard Downstream Port, it may not be possible
> > to reliably pull 500mA - depending on cable quality and source
> 
> "configured"?
> 
> > quality I have reports of charging failure due to the voltage dropping
> > too low.
> > 
> > To address both these concern, this patch introduce incremental
> 
> concerns.
> 
> > current setting.
> > The current pull from VBUS is increased in steps of 20mA every 100ms
> > until the target is reached or until the measure voltage drops below
> > 4.75V.  If the voltage does go too long, the target current is reduced
> 
> "too low"?
> 
> > by 20mA and kept there.
> > 
> > This applies to currents selected automatically, or to values
> > set via sysfs.  So setting a large value will cause the maximum
> > available to be used - up to the limit of 1.7mA imposed by the
> > hardware.
> 
> 1.7A?
> 
> 
> > @@ -249,8 +261,14 @@ static int twl4030_charger_update_current(struct twl4030_bci *bci)
> >  		cur = bci->ac_cur;
> >  		bci->ac_is_active = 1;
> >  	} else {
> > -		cur = bci->usb_cur;
> > +		cur = bci->usb_cur_actual;
> 
> usb_cur_actual is not a really great variable name...

I changed "usb_cur" to "usb_cur_target" and
"usb_cur_actual" to "usb_cur".

> 
> >  		bci->ac_is_active = 0;
> > +		if (cur > bci->usb_cur) {
> > +			cur = bci->usb_cur;
> > +			bci->usb_cur_actual = cur;
> > +		}
> > +		if (cur < bci->usb_cur)
> > +			schedule_delayed_work(&bci->current_worker, USB_CUR_DELAY);
> >  	}
> >  
> >  	/* First, check thresholds and see if cgain is needed */
> > @@ -379,6 +397,38 @@ static int twl4030_charger_update_current(struct twl4030_bci *bci)
> >  	return 0;
> >  }
> >  
> > +static void twl4030_current_worker(struct work_struct *data)
> > +{
> > +	int v;
> > +	int res;
> > +	struct twl4030_bci *bci = container_of(data, struct twl4030_bci,
> > +					       current_worker.work);
> > +
> > +	res = twl4030bci_read_adc_val(TWL4030_BCIVBUS);
> > +	if (res < 0)
> > +		v = 0;
> > +	else
> > +		/* BCIVBUS uses ADCIN8, 7/1023 V/step */
> > +		v = res * 6843;
> > +
> > +	printk("v=%d cur=%d target=%d\n", v, bci->usb_cur_actual,
> > +	       bci->usb_cur);
> > +
> > +	if (v < USB_MIN_VOLT) {
> > +		/* Back up and stop adjusting. */
> > +		bci->usb_cur_actual -= USB_CUR_STEP;
> > +		bci->usb_cur = bci->usb_cur_actual;
> > +	} else if (bci->usb_cur_actual >= bci->usb_cur ||
> > +		   bci->usb_cur_actual + USB_CUR_STEP > USB_MAX_CURRENT) {
> > +		/* Reach target and volts are OK - stop */
> 
> Reached ... and the voltage is OK - stop.
> 
> 

Thanks for all your proof-reading :-)

NeilBrown

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