There are fuel gauges in the bq27xxx series (e.g. bq27z561) which may in some
cases report 0xff as the value of BQ27XXX_REG_FLAGS that should not be
interpreted as "no battery" like for a disconnected battery with some built
in bq27000 chip.

So restrict the no-battery detection originally introduced by

    commit 3dd843e1c26a ("bq27000: report missing device better.")

to the bq27000.

There is no need to backport further because this was hidden before

	commit f16d9fb6cf03 ("power: supply: bq27xxx: Retrieve again when busy")

Fixes: f16d9fb6cf03 ("power: supply: bq27xxx: Retrieve again when busy")
Suggested-by: Jerry Lv <Jerry.Lv@axis.com>
Cc: stable@vger.kernel.org
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
---
 drivers/power/supply/bq27xxx_battery.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
index dadd8754a73a8..3363af24017ae 100644
--- a/drivers/power/supply/bq27xxx_battery.c
+++ b/drivers/power/supply/bq27xxx_battery.c
@@ -1944,8 +1944,8 @@ static void bq27xxx_battery_update_unlocked(struct bq27xxx_device_info *di)
 	bool has_singe_flag = di->opts & BQ27XXX_O_ZERO;
 
 	cache.flags = bq27xxx_read(di, BQ27XXX_REG_FLAGS, has_singe_flag);
-	if ((cache.flags & 0xff) == 0xff)
-		cache.flags = -ENODEV; /* read error */
+	if (di->chip == BQ27000 && (cache.flags & 0xff) == 0xff)
+		cache.flags = -ENODEV; /* bq27000 hdq read error */
 	if (cache.flags >= 0) {
 		cache.capacity = bq27xxx_battery_read_soc(di);
 
-- 
2.50.1

On 8/23/2025 6:34 PM, H. Nikolaus Schaller wrote:
> There are fuel gauges in the bq27xxx series (e.g. bq27z561) which may in some
> cases report 0xff as the value of BQ27XXX_REG_FLAGS that should not be
> interpreted as "no battery" like for a disconnected battery with some built
> in bq27000 chip.
>
> So restrict the no-battery detection originally introduced by
>
>      commit 3dd843e1c26a ("bq27000: report missing device better.")
>
> to the bq27000.
>
> There is no need to backport further because this was hidden before
>
> 	commit f16d9fb6cf03 ("power: supply: bq27xxx: Retrieve again when busy")
>
> Fixes: f16d9fb6cf03 ("power: supply: bq27xxx: Retrieve again when busy")
> Suggested-by: Jerry Lv <Jerry.Lv@axis.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
> ---
>   drivers/power/supply/bq27xxx_battery.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
> index dadd8754a73a8..3363af24017ae 100644
> --- a/drivers/power/supply/bq27xxx_battery.c
> +++ b/drivers/power/supply/bq27xxx_battery.c
> @@ -1944,8 +1944,8 @@ static void bq27xxx_battery_update_unlocked(struct bq27xxx_device_info *di)
>   	bool has_singe_flag = di->opts & BQ27XXX_O_ZERO;
>   
>   	cache.flags = bq27xxx_read(di, BQ27XXX_REG_FLAGS, has_singe_flag);
> -	if ((cache.flags & 0xff) == 0xff)
> -		cache.flags = -ENODEV; /* read error */
> +	if (di->chip == BQ27000 && (cache.flags & 0xff) == 0xff)
> +		cache.flags = -ENODEV; /* bq27000 hdq read error */
>   	if (cache.flags >= 0) {
>   		cache.capacity = bq27xxx_battery_read_soc(di);
>   

This change works fine for BQ27z561

> Am 28.08.2025 um 09:33 schrieb Jerry Lv <jerrylv@axis.com>:
> 
> On 8/23/2025 6:34 PM, H. Nikolaus Schaller wrote:
>> There are fuel gauges in the bq27xxx series (e.g. bq27z561) which may in some
>> cases report 0xff as the value of BQ27XXX_REG_FLAGS that should not be
>> interpreted as "no battery" like for a disconnected battery with some built
>> in bq27000 chip.
>> 
>> So restrict the no-battery detection originally introduced by
>> 
>>     commit 3dd843e1c26a ("bq27000: report missing device better.")
>> 
>> to the bq27000.
>> 
>> There is no need to backport further because this was hidden before
>> 
>> 	commit f16d9fb6cf03 ("power: supply: bq27xxx: Retrieve again when busy")
>> 
>> Fixes: f16d9fb6cf03 ("power: supply: bq27xxx: Retrieve again when busy")
>> Suggested-by: Jerry Lv <Jerry.Lv@axis.com>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
>> ---
>>  drivers/power/supply/bq27xxx_battery.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/power/supply/bq27xxx_battery.c b/drivers/power/supply/bq27xxx_battery.c
>> index dadd8754a73a8..3363af24017ae 100644
>> --- a/drivers/power/supply/bq27xxx_battery.c
>> +++ b/drivers/power/supply/bq27xxx_battery.c
>> @@ -1944,8 +1944,8 @@ static void bq27xxx_battery_update_unlocked(struct bq27xxx_device_info *di)
>>  	bool has_singe_flag = di->opts & BQ27XXX_O_ZERO;
>>    	cache.flags = bq27xxx_read(di, BQ27XXX_REG_FLAGS, has_singe_flag);
>> -	if ((cache.flags & 0xff) == 0xff)
>> -		cache.flags = -ENODEV; /* read error */
>> +	if (di->chip == BQ27000 && (cache.flags & 0xff) == 0xff)
>> +		cache.flags = -ENODEV; /* bq27000 hdq read error */
>>  	if (cache.flags >= 0) {
>>  		cache.capacity = bq27xxx_battery_read_soc(di);
>>  
> 
> This change works fine for BQ27z561

Thanks for testing!

So it appears we need a maintainer to pick up these patches...

BR,
Nikolaus