linux-kernel - Re: [PATCH v3] power: supply: bq27xxx: Retrieve again when busy

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Message-ID: <20250319203629.zb6zob5nqapr2faw@pali>
Date: Wed, 19 Mar 2025 21:36:29 +0100
From: Pali Rohár <pali@...nel.org>
To: Jerry Lv <Jerry.Lv@...s.com>
Cc: Sebastian Reichel <sre@...nel.org>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel@...s.com
Subject: Re: [PATCH v3] power: supply: bq27xxx: Retrieve again when busy

On Wednesday 19 March 2025 17:41:28 Jerry Lv wrote:
> Multiple applications may access the battery gauge at the same time, so
> the gauge may be busy and EBUSY will be returned. The driver will set a
> flag to record the EBUSY state, and this flag will be kept until the next
> periodic update. When this flag is set, bq27xxx_battery_get_property()
> will just return ENODEV until the flag is updated.
> 
> Even if the gauge was busy during the last accessing attempt, returning
> ENODEV is not ideal, and can cause confusion in the applications layer.
> 
> Instead, retry accessing the I2C to update the flag is as expected, for
> the gauge typically recovers from busy state within a few milliseconds.
> If still failed to access the gauge, the real error code would be returned
> instead of ENODEV (as suggested by Pali Rohár).
> 
> Signed-off-by: Jerry Lv <Jerry.Lv@...s.com>
> ---
> Changes in v3:
> - Move I2C retry logic to bq27xxx_battery_i2c_read()
> - Link to v2: https://lore.kernel.org/all/20241029-foo-fix-v1-1-1dbfed72d023@axis.com
> 
> Changes in v2:
> - Retry up to 3 times when gauge is busy
> - return the real error code when fail to access the device
> - Link to v1: https://lore.kernel.org/all/20240913-foo-fix2-v1-1-a0f499404f3a@axis.com
> ---
>  drivers/power/supply/bq27xxx_battery.c     |  2 +-
>  drivers/power/supply/bq27xxx_battery_i2c.c | 15 ++++++++++++++-
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
> index 750fda543308..99631ab46e8e 100644
> --- a/drivers/power/supply/bq27xxx_battery.c
> +++ b/drivers/power/supply/bq27xxx_battery.c
> @@ -2030,7 +2030,7 @@ static int bq27xxx_battery_get_property(struct power_supply *psy,
>  	mutex_unlock(&di->lock);
>  
>  	if (psp != POWER_SUPPLY_PROP_PRESENT && di->cache.flags < 0)
> -		return -ENODEV;
> +		return di->cache.flags;
>  
>  	switch (psp) {
>  	case POWER_SUPPLY_PROP_STATUS:
> diff --git a/drivers/power/supply/bq27xxx_battery_i2c.c b/drivers/power/supply/bq27xxx_battery_i2c.c
> index ba0d22d90429..78cccea4d419 100644
> --- a/drivers/power/supply/bq27xxx_battery_i2c.c
> +++ b/drivers/power/supply/bq27xxx_battery_i2c.c
> @@ -6,6 +6,7 @@
>   *	Andrew F. Davis <afd@...com>
>   */
>  
> +#include <linux/delay.h>
>  #include <linux/i2c.h>
>  #include <linux/interrupt.h>
>  #include <linux/module.h>
> @@ -27,10 +28,15 @@ static irqreturn_t bq27xxx_battery_irq_handler_thread(int irq, void *data)
>  static int bq27xxx_battery_i2c_read(struct bq27xxx_device_info *di, u8 reg,
>  				    bool single)
>  {
> +#define MAX_RETRY 3
> +#define I2C_DELAY_MIN 10000
> +#define I2C_DELAY_MAX 11000
> +
>  	struct i2c_client *client = to_i2c_client(di->dev);
>  	struct i2c_msg msg[2];
>  	u8 data[2];
>  	int ret;
> +	int retry = 0;
>  
>  	if (!client->adapter)
>  		return -ENODEV;
> @@ -47,7 +53,14 @@ static int bq27xxx_battery_i2c_read(struct bq27xxx_device_info *di, u8 reg,
>  	else
>  		msg[1].len = 2;
>  
> -	ret = i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg));
> +	do {
> +		ret = i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg));
> +		if (ret == -EBUSY && retry < MAX_RETRY) {
> +			retry++;
> +			/* sleep 10 miliseconds when busy */
> +			usleep_range(I2C_DELAY_MIN, I2C_DELAY_MAX);
> +		}
> +	} while (ret == -EBUSY && retry < MAX_RETRY);
>  	if (ret < 0)
>  		return ret;
>  
> 
> ---
> base-commit: 42f7652d3eb527d03665b09edac47f85fb600924
> change-id: 20241008-foo-fix-b2244cbe6dce
> 
> Best regards,
> -- 
> Jerry Lv <Jerry.Lv@...s.com>
> 

Hello, this change looks good. I think that now it should handle all
cases when chipset is busy.

Personally if I'm writing this change I will avoid those new ad-hoc
#defines in the middle of the function and also avoid duplicating the
loop terminating condition (there is two times). For example as:

    retry = 0;
    do {
        ret = i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg));
        if (ret == -EBUSY && ++retry < 3) {
            /* sleep 10 milliseconds when busy */
            usleep_range(10000, 11000);
            continue;
        }
        break;
    } while (0);

Btw, "milliseconds" should be with two LL.

But I will let the code style decision to maintainers.

Reviewed-by: Pali Rohár <pali@...nel.org>