[Gta04-owner] [PATCH 14/15] twl4030_charger: Increase current carefully while watching voltage.

[EdorFaus]

On 02/24/2015 05:33 AM, 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
> quality I have reports of charging failure due to the voltage dropping
> too low.
> 
> To address both these concern, this patch introduce incremental
> 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
> 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.

As 1.7mA makes little sense here, I assume this should say 1.7A?

The relative values of USB_CUR_STEP and USB_MAX_CURRENT seem to agree.

> 
> Signed-off-by: NeilBrown <neilb at suse.de>
> ---
>  drivers/power/twl4030_charger.c |   54 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 53 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/power/twl4030_charger.c b/drivers/power/twl4030_charger.c
> index e5a0225ea87e..7ad6b4b531d7 100644
> --- a/drivers/power/twl4030_charger.c
> +++ b/drivers/power/twl4030_charger.c
> @@ -117,6 +117,18 @@ struct twl4030_bci {
>  #define	CHARGE_AUTO	1
>  #define	CHARGE_LINEAR	2
>  
> +	/* When setting the USB current we slowly increase the
> +	 * requested current until target is reached or the voltage
> +	 * drops below 4.75V.  In the latter case we set back one
> +	 * step.
> +	 */
> +	int			usb_cur_actual;
> +	struct delayed_work	current_worker;
> +#define	USB_CUR_STEP	20000	/* 20mA at a time */
> +#define	USB_MIN_VOLT	4750000	/* 4.75V */
> +#define	USB_CUR_DELAY	msecs_to_jiffies(100)
> +#define	USB_MAX_CURRENT	1700000 /* TWL4030 caps at 1.7mA */

As above, this comment should probably say 1.7A, or 1700mA, not 1.7mA.


By the way, I agree with Boudewijn: even though I don't really know what
I'm doing when it comes to kernel code, it's still interesting, so
thanks for posting the patches here. :)

Best regards,
Frode Austvik

> +
>  	unsigned long		event;
>  };
>  
> @@ -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;
>  		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 */
> +		return;
> +	} else {
> +		bci->usb_cur_actual += USB_CUR_STEP;
> +		schedule_delayed_work(&bci->current_worker, USB_CUR_DELAY);
> +	}
> +	twl4030_charger_update_current(bci);
> +}
> +
>  /*
>   * Enable/Disable USB Charge functionality.
>   */
> @@ -441,6 +491,7 @@ static int twl4030_charger_enable_usb(struct twl4030_bci *bci, bool enable)
>  			pm_runtime_put_autosuspend(bci->transceiver->dev);
>  			bci->usb_enabled = 0;
>  		}
> +		bci->usb_cur_actual = 0;
>  	}
>  
>  	return ret;
> @@ -972,6 +1023,7 @@ static int __init twl4030_bci_probe(struct platform_device *pdev)
>  	}
>  
>  	INIT_WORK(&bci->work, twl4030_bci_usb_work);
> +	INIT_DELAYED_WORK(&bci->current_worker, twl4030_current_worker);
>  
>  	bci->usb_nb.notifier_call = twl4030_bci_usb_ncb;
>  	if (bci->dev->of_node) {
> 
> 
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