linux-kernel - Re: v4.10-rc4 to v4.10-rc5: battery regression on Nokia N900

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Date:   Fri, 27 Jan 2017 09:37:10 +0800
From:   Zhang Rui <rui.zhang@...el.com>
To:     Pali Rohár <pali.rohar@...il.com>,
        Pavel Machek <pavel@....cz>
Cc:     Guenter Roeck <linux@...ck-us.net>, sre@...nel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-omap@...r.kernel.org, tony@...mide.com, khilman@...nel.org,
        aaro.koskinen@....fi, ivo.g.dimitrov.75@...il.com,
        patrikbachan@...il.com, serge@...lyn.com, abcloriens@...il.com,
        fabio.estevam@....com
Subject: Re: v4.10-rc4 to v4.10-rc5: battery regression on Nokia N900

On Wed, 2017-01-25 at 13:09 +0100, Pali Rohár wrote:
> On Wednesday 25 January 2017 12:12:33 Pavel Machek wrote:
> > 
> > Hi!
> > 
> > > 
> > > > 
> > > > > 
> > > > > > 
> > > > > > > 
> > > > > > > Right.
> > > > > > > 
> > > > > > > Before reverting, can you please try if this patch works
> > > > > > > or not?
> > > > > > Not really. Revert now. Sorry.
> > > > > > 
> > > > > > Are you sure? This does not look equivalent to me at all.
> > > > > > 
> > > > > > "name" file handling moved from drivers to the core, which
> > > > > > added some
> > > > > > crazy checks what name can contain. Even if this "works",
> > > > > > what is the
> > > > > > expected effect on the "name" file?
> > > > > > 
> > > > > The hwmon name attribute must not include '-', as documented
> > > > > in
> > > > > Documentation/hwmon/sysfs-interface. Is enforcing that
> > > > > 'crazy' ?
> > > > > Maybe in your world, but not in mine.
> > > > Well, lets revert the patch and then we can discuss what to do
> > > > with
> > > > the "name" problem.
> > Ok, so the patch is on the way in. What to do next?
> > 
> > pavel@...0:/sys/class/hwmon$ cat hwmon0/name
> > bq27200-0
> > pavel@...0:/sys/class/hwmon$ cat hwmon1/name
> > rx51-battery
> > 
> > > 
> > > To provide some detail: libsensors gets just as confused with
> > > wildcards
> > > and whitespace/newline as it does with '-' in the reported name,
> > > which
> > > is why those are blocked by the new API.
> > Ok... Question is "does someone actually use hwmon*/name on N900"?
> > If
> > so, we can't change it, but it is well possible that noone is.
> IIRC hwmon is used on Nokia N900.
> 
> But I have not seen hwmon devices for bq27200 and rx51-battery yet.
> Those are power supply driver and auto-exporting them also via hwmon
> is
> something new, right? If yes, then we can use any name for those new
> hwmon devices as they cannot break userspace... as there is no
> userspace
> application for them.
> 
If this is the case, you'd better set
(struct thermal_zone_params)->no_hwmon when registering the thermal
zone device, in which case, the hwmon device will not be created.

In fact, I'd prefer to change tzp->no_hwmon to tzp->hwmon to not create
hwmon I/F by default, and see if there is anyone using it. If yes, we
can set the flag in soc thermal driver, explicitly, at meantime, a
hwmon compatible name is required.

But one foreseeable result is that we may get bug reports from end user
that some sensors (acpitz, etc) are gone in 'sensors' output. And TBH,
I'm not quite sure if this can be counted as a regression or not.

thanks,
rui
> > 
> > Next question is .. are there other drivers affected? Do we want to
> > do
> > '-' -> '_' in the core or somewhere in the drivers? We might want
> > to
> > do the change in early in 4.11 and see what breaks....
> IIRC hwmon core does not accept '-' for a long time (maybe all 4.x
> versions?).
>