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

Pavel Machek
2015-03-02T21:29:52Z

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...

> 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.

--
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