linux-kernel - Re: [PATCH] power: max8925_power: Fix incorrect voltage and current calculation

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Message-ID: <CAN1soZxYu8M_i8zFET0k_6KTVumNSxMGWL2Yp7NFd05f_oSw9g@mail.gmail.com>
Date:	Sat, 27 Aug 2011 07:11:42 +0800
From:	Haojian Zhuang <haojian.zhuang@...il.com>
To:	Philip Rakity <prakity@...vell.com>,
	David Woodhouse <dwmw2@...radead.org>, cbou@...l.ru
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] power: max8925_power: Fix incorrect voltage and current calculation

On Sat, Aug 27, 2011 at 4:28 AM, Philip Rakity <prakity@...vell.com> wrote:
>
> The datasheet indicates a 12 bit value is returned for i2c
> registers for voltage and current.  Code was assuming 8 bits.
> But default for chip is 12 bit return value.
>
> Voltage is returned in 2mV units  -- adjust to return as uV
> per linux power spec
>
> Adjust current calculation to return units in uA
> *** NOT POSSIBLE TO VALIDATE THIS since my h/w does not have
> current hooked up to 8925 *****
>
> Signed-off-by: Philip Rakity <prakity@...vell.com>
> ---
>  drivers/power/max8925_power.c |   13 ++++++-------
>  1 files changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/power/max8925_power.c b/drivers/power/max8925_power.c
> index 29b5d2c..5e4e046 100644
> --- a/drivers/power/max8925_power.c
> +++ b/drivers/power/max8925_power.c
> @@ -190,7 +190,7 @@ static int start_measure(struct max8925_power_info *info, int type)
>        }
>
>        max8925_bulk_read(info->adc, meas_reg, 2, buf);
> -       ret = (buf[0] << 4) | (buf[1] >> 4);
> +       ret = ((buf[0]<<8) | buf[1]) >> 4;
>
>        return ret;
>  }
> @@ -210,7 +210,7 @@ static int max8925_ac_get_prop(struct power_supply *psy,
>                if (info->ac_online) {
>                        ret = start_measure(info, MEASURE_VCHG);
>                        if (ret >= 0) {
> -                               val->intval = ret << 1; /* unit is mV */
> +                               val->intval = ret * 2000;       /* unit is uV */
>                                goto out;
>                        }
>                }
> @@ -244,7 +244,7 @@ static int max8925_usb_get_prop(struct power_supply *psy,
>                if (info->usb_online) {
>                        ret = start_measure(info, MEASURE_VCHG);
>                        if (ret >= 0) {
> -                               val->intval = ret << 1; /* unit is mV */
> +                               val->intval = ret * 2000;       /* unit is uV */
>                                goto out;
>                        }
>                }
> @@ -268,7 +268,6 @@ static int max8925_bat_get_prop(struct power_supply *psy,
>                                union power_supply_propval *val)
>  {
>        struct max8925_power_info *info = dev_get_drvdata(psy->dev->parent);
> -       long long int tmp = 0;
>        int ret = 0;
>
>        switch (psp) {
> @@ -279,7 +278,7 @@ static int max8925_bat_get_prop(struct power_supply *psy,
>                if (info->bat_online) {
>                        ret = start_measure(info, MEASURE_VMBATT);
>                        if (ret >= 0) {
> -                               val->intval = ret << 1; /* unit is mV */
> +                               val->intval = ret * 2000;       /* unit is uV */
>                                ret = 0;
>                                break;
>                        }
> @@ -290,8 +289,8 @@ static int max8925_bat_get_prop(struct power_supply *psy,
>                if (info->bat_online) {
>                        ret = start_measure(info, MEASURE_ISNS);
>                        if (ret >= 0) {
> -                               tmp = (long long int)ret * 6250 / 4096 - 3125;
> -                               ret = (int)tmp;
> +                               /* assume r_sns is 0.02 */
> +                               ret = ((ret * 6250) - 3125) /* uA */;
>                                val->intval = 0;
>                                if (ret > 0)
>                                        val->intval = ret; /* unit is mA */
> --
> 1.7.6
>

Loop maintainer
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