linux-kernel - Re: [PATCH] power: supply: bq27xxx_battery: Retrieve again when busy

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Message-ID: <20241029165646.x5wqy5bo5cjv2q4e@pali>
Date: Tue, 29 Oct 2024 17:56:46 +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] power: supply: bq27xxx_battery: Retrieve again when busy

On Tuesday 29 October 2024 11:35:00 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 gauge 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>
> ---
> When the battery gauge is busy, retry to access 10 miliseconds later,
> retry up to 3 times. When failed to access the gauge, return the real
> error code.
> 
> Differences related to previous versions:
> v2 (as suggested by Pali Rohár):
> - retry up to 3 times when gauge is busy.
> - return the real error code when fail to access the device.
> 
> v1:
> - initial version for review.
> ---
>  drivers/power/supply/bq27xxx_battery.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
> index 750fda543308..9c40bbc292c1 100644
> --- a/drivers/power/supply/bq27xxx_battery.c
> +++ b/drivers/power/supply/bq27xxx_battery.c
> @@ -1871,11 +1871,19 @@ static int bq27xxx_battery_current_and_status(
>  
>  static void bq27xxx_battery_update_unlocked(struct bq27xxx_device_info *di)
>  {
> +#define MAX_RETRY 3
> +	int retry = 0, sleep = 10;
>  	union power_supply_propval status = di->last_status;
>  	struct bq27xxx_reg_cache cache = {0, };
>  	bool has_singe_flag = di->opts & BQ27XXX_O_ZERO;
>  
> -	cache.flags = bq27xxx_read(di, BQ27XXX_REG_FLAGS, has_singe_flag);
> +	do {
> +		cache.flags = bq27xxx_read(di, BQ27XXX_REG_FLAGS, has_singe_flag);
> +		if (cache.flags == -EBUSY && retry < MAX_RETRY) {
> +			retry++;
> +			BQ27XXX_MSLEEP(sleep);		/* sleep 10 miliseconds when busy */
> +		}
> +	} while (cache.flags == -EBUSY && retry < MAX_RETRY);

Hello, this is for sure nice improvement.

Anyway, I think that I mentioned it in previous email, this problem
which you describe does not affect only bq27xxx_battery_update_unlocked()
but also any other function which calls bq27xxx_read().

What about rather moving this -EBUSY retry logic into the bq27xxx_read()
function itself? Or even better, directly inside bq27xxx_battery_i2c_read()
function? This would fix this problem on all places.

>  	if ((cache.flags & 0xff) == 0xff)
>  		cache.flags = -1; /* read error */
>  	if (cache.flags >= 0) {
> @@ -2030,7 +2038,7 @@ 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:
> 
> ---
> base-commit: 42f7652d3eb527d03665b09edac47f85fb600924
> change-id: 20241008-foo-fix-b2244cbe6dce
> 
> Best regards,
> -- 
> Jerry Lv <Jerry.Lv@...s.com>
>