Multiple applications may access the device 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 properties is as expected.
The gauge typically recovers from busy state within a few milliseconds, and
the cached flag will not cause issues while updating the properties.

Signed-off-by: Jerry Lv <Jerry.Lv@axis.com>
---
 drivers/power/supply/bq27xxx_battery.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
index 750fda543308..eefbb5029a3b 100644
--- a/drivers/power/supply/bq27xxx_battery.c
+++ b/drivers/power/supply/bq27xxx_battery.c
@@ -2029,7 +2029,7 @@ static int bq27xxx_battery_get_property(struct power_supply *psy,
 		bq27xxx_battery_update_unlocked(di);
 	mutex_unlock(&di->lock);
 
-	if (psp != POWER_SUPPLY_PROP_PRESENT && di->cache.flags < 0)
+	if (psp != POWER_SUPPLY_PROP_PRESENT && di->cache.flags < 0 && di->cache.flags != -EBUSY)
 		return -ENODEV;
 
 	switch (psp) {

---
base-commit: da3ea35007d0af457a0afc87e84fddaebc4e0b63
change-id: 20240913-foo-fix2-a0d79db86a0b

Best regards,
-- 
Jerry Lv <Jerry.Lv@axis.com>

On Friday 13 September 2024 16:45:37 Jerry Lv wrote:
> Multiple applications may access the device 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.

I did not find any evidence of EBUSY. Which function and to which caller
it returns? Do you mean that bq27xxx_read() returns -EBUSY?

> Even if the gauge was busy during the last accessing attempt, returning
> ENODEV is not ideal, and can cause confusion in the applications layer.

It would be better to either propagate correct error or return old value
from cache...

> Instead, retry accessing the gauge to update the properties is as expected.
> The gauge typically recovers from busy state within a few milliseconds, and
> the cached flag will not cause issues while updating the properties.
> 
> Signed-off-by: Jerry Lv <Jerry.Lv@axis.com>
> ---
>  drivers/power/supply/bq27xxx_battery.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
> index 750fda543308..eefbb5029a3b 100644
> --- a/drivers/power/supply/bq27xxx_battery.c
> +++ b/drivers/power/supply/bq27xxx_battery.c
> @@ -2029,7 +2029,7 @@ static int bq27xxx_battery_get_property(struct power_supply *psy,
>  		bq27xxx_battery_update_unlocked(di);
>  	mutex_unlock(&di->lock);
>  
> -	if (psp != POWER_SUPPLY_PROP_PRESENT && di->cache.flags < 0)
> +	if (psp != POWER_SUPPLY_PROP_PRESENT && di->cache.flags < 0 && di->cache.flags != -EBUSY)
>  		return -ENODEV;

... but ignoring error and re-using the error return value as flags in
code later in this function is bad idea.

>  
>  	switch (psp) {
> 
> ---
> base-commit: da3ea35007d0af457a0afc87e84fddaebc4e0b63
> change-id: 20240913-foo-fix2-a0d79db86a0b
> 
> Best regards,
> -- 
> Jerry Lv <Jerry.Lv@axis.com>
>