linux-kernel - Re: [PATCH] power: supply: bq27xxx: fix error return in case of no bq27000 hdq battery

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Message-ID: <20250821201544.047e54e9@akair>
Date: Thu, 21 Aug 2025 20:15:44 +0200
From: Andreas Kemnade <andreas@...nade.info>
To: "H. Nikolaus Schaller" <hns@...delico.com>
Cc: Sebastian Reichel <sre@...nel.org>, Jerry Lv <Jerry.Lv@...s.com>, Pali
 Rohár <pali@...nel.org>, linux-pm@...r.kernel.org,
 linux-kernel@...r.kernel.org, letux-kernel@...nphoenux.org,
 stable@...r.kernel.org, kernel@...a-handheld.com
Subject: Re: [PATCH] power: supply: bq27xxx: fix error return in case of no
 bq27000 hdq battery

Hi,

Am Mon, 21 Jul 2025 14:46:09 +0200
schrieb "H. Nikolaus Schaller" <hns@...delico.com>:

> Since commit
> 
> commit f16d9fb6cf03 ("power: supply: bq27xxx: Retrieve again when busy")
> 
> the console log of some devices with hdq but no bq27000 battery
> (like the Pandaboard) is flooded with messages like:
> 
> [   34.247833] power_supply bq27000-battery: driver failed to report 'status' property: -1
> 
> as soon as user-space is finding a /sys entry and trying to read the
> "status" property.
> 
> It turns out that the offending commit changes the logic to now return the
> value of cache.flags if it is <0. This is likely under the assumption that
> it is an error number. In normal errors from bq27xxx_read() this is indeed
> the case.
> 
> But there is special code to detect if no bq27000 is installed or accessible
> through hdq/1wire and wants to report this. In that case, the cache.flags
> are set (historically) to constant -1 which did make reading properties
> return -ENODEV. So everything appeared to be fine before the return value was
> fixed. Now the -1 is returned as -ENOPERM instead of -ENODEV, triggering the
> error condition in power_supply_format_property() which then floods the
> console log.
> 
> So we change the detection of missing bq27000 battery to simply set
> 
> 	cache.flags = -ENODEV
> 
> instead of -1.
> 
This all is a bit inconsistent, the offending commit makes it worse. 
Normally devices appear only in /sys if they exist. Regarding stuff in
/sys/class/power_supply, input power supplies might be there or not,
but there you can argument that the entry in /sys/class/power_supply
only means that there is a connector for connecting a supply.
But having the battery entry everywhere looks like waste. If would
expect the existence of a battery bay in the device where the common
battery is one with a bq27xxx.

Regards,
Andreas