On Mon, 2 Mar 2015 22:29:45 +0100 Pavel Machek <pa...@ucw.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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