linux-kernel - Re: [PATCH 1/2] power: supply: sbs-battery: Prevent CAPACITY

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Date:   Tue, 13 Jun 2017 11:15:23 -0700
From:   Guenter Roeck <groeck@...gle.com>
To:     Shawn Nematbakhsh <shawnn@...omium.org>
Cc:     Sebastian Reichel <sre@...nel.org>, linux-pm@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Guenter Roeck <groeck@...omium.org>
Subject: Re: [PATCH 1/2] power: supply: sbs-battery: Prevent CAPACITY_MODE races

On Tue, Jun 13, 2017 at 10:53 AM, Shawn Nematbakhsh <shawnn@...omium.org> wrote:
> A subset of smart battery commands return charge or energy depending on
> the CAPACITY_MODE bit setting of BatteryMode(). In order to
> unambiguously read a charge or energy value, it is necessary to ensure
> that CAPACITY_MODE is set as desired, and not changed for the duration
> of the attribute read.
>
> Signed-off-by: Shawn Nematbakhsh <shawnn@...omium.org>

Reviewed-by: Guenter Roeck <groeck@...omium.org>

> ---
>  drivers/power/supply/sbs-battery.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/power/supply/sbs-battery.c b/drivers/power/supply/sbs-battery.c
> index e3a114e60f1a..d7e68fd97099 100644
> --- a/drivers/power/supply/sbs-battery.c
> +++ b/drivers/power/supply/sbs-battery.c
> @@ -171,6 +171,7 @@ struct sbs_info {
>         u32                             i2c_retry_count;
>         u32                             poll_retry_count;
>         struct delayed_work             work;
> +       struct mutex                    mode_lock;
>  };
>
>  static char model_name[I2C_SMBUS_BLOCK_MAX + 1];
> @@ -623,7 +624,13 @@ static int sbs_get_property(struct power_supply *psy,
>                 if (ret < 0)
>                         break;
>
> +               /* sbs_get_battery_capacity() will change the battery mode
> +                * temporarily to read the requested attribute. Ensure we stay
> +                * in the desired mode for the duration of the attribute read.
> +                */
> +               mutex_lock(&chip->mode_lock);
>                 ret = sbs_get_battery_capacity(client, ret, psp, val);
> +               mutex_unlock(&chip->mode_lock);
>                 break;
>
>         case POWER_SUPPLY_PROP_SERIAL_NUMBER:
> @@ -808,6 +815,7 @@ static int sbs_probe(struct i2c_client *client,
>         psy_cfg.of_node = client->dev.of_node;
>         psy_cfg.drv_data = chip;
>         chip->last_state = POWER_SUPPLY_STATUS_UNKNOWN;
> +       mutex_init(&chip->mode_lock);
>
>         /* use pdata if available, fall back to DT properties,
>          * or hardcoded defaults if not
> --
> 2.13.1.508.gb3defc5cc-goog
>