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SubjectRe: [PATCH 14/15] twl4030_charger: Increase current carefully while watching voltage.
On Mon, 2 Mar 2015 22:29:45 +0100 Pavel Machek <pavel@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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