linux-kernel - Re: [PATCH v3 00/19] Report power supply from hid-logitech-hidpp

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Date:   Mon, 05 Jun 2017 15:09:34 +0200
From:   Bastien Nocera <hadess@...ess.net>
To:     Jiri Kosina <jikos@...nel.org>, Dave Hansen <dave.hansen@...el.com>
Cc:     Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/19] Report power supply from hid-logitech-hidpp

On Mon, 2017-06-05 at 10:01 +0200, Jiri Kosina wrote:
> On Fri, 2 Jun 2017, Dave Hansen wrote:
> 
> > > > > > This will allow upower to not handle those devices anymore
> > > > > > and to
> > > > > > have more
> > > > > > immediate reportng of the device to the system.
> > > > > 
> > > > > FWIW, I'm on Ubuntu 14.04, and upower *is* reporting my mouse
> > > > > battery
> > > > > as
> > > > > if it were a laptop battery.  It's mostly garbage, and always
> > > > > reports
> > > > > 0%, which makes upower always tell me my laptop is 2/3
> > > > > charged (I
> > > > > have 2
> > > > > real batteries).
> > > 
> > > Well, the exported battery might be sending levels instead of
> > > pourcentages. And upower needs to be upgraded to handle those :(
> > 
> > It sounds like there are a number of things here where newer
> > kernels are
> > breaking older userspace.  It's also causing some very end-user
> > visible
> > effects, like having folks' systems auto shut down because upower
> > thinks
> > their batteries are dead.
> > 
> > Old versions of upower are obviously confused here.  It would be
> > really
> > nice to ensure that newer kernels don't break it like this.
> > 
> > IOW, it would be really nice if this were treated like a
> > regression,
> > because it's tantalizingly close.
> 
> I agree with Dave. If there is no solution found in time for -rc5, 
> reverting to previous state would be the proper way to go.

I don't see how it's possible to retroactively fix user-space. The best
(but oh so backwards) way to fix this might be to wrap the
functionality in a config option, for user-spaces that can't update
their version of UPower.

I still think it's counter-productive, the only consumer for this
information is UPower, and it's been modified to work-around the fact
that the kernel didn't export this battery information. It now does.