linux-kernel - Re: [PATCH v3 0/3] thermal: introduce by-name softlink

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Date:   Wed, 11 Dec 2019 09:53:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Wei Wang <wvw@...gle.com>, Wei Wang <wei.vince.wang@...il.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Amit Kucheria <amit.kucheria@...durent.com>,
        Linux PM list <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v3 0/3] thermal: introduce by-name softlink

On Tue, Dec 10, 2019 at 09:54:11PM +0100, Daniel Lezcano wrote:
> On 10/12/2019 21:01, Wei Wang wrote:
> > On Tue, Dec 10, 2019 at 6:36 AM Daniel Lezcano
> > <daniel.lezcano@...aro.org> wrote:
> >>
> >> On 05/12/2019 08:19, Wei Wang wrote:
> >>> The paths thermal_zone%d and cooling_device%d are not intuitive and the
> >>> numbers are subject to change due to device tree change. This usually
> >>> leads to tree traversal in userspace code.
> >>> The patch creates `tz-by-name' and `cdev-by-name' for thermal zone and
> >>> cooling_device respectively.
> >>
> >> Instead of adding another ABI, I suggest we put the current one
> >> deprecated with a warning in the dmesg, update the documentation and
> >> change the name the next version.
> >>
> >>
> > 
> > IMHO, we should keep the existing path which is a common pattern for
> > sysfs interface. There are reasons we need couple thermal zone and
> > cooling device in one class, but might be worth considering split as
> > the latter might be used for other purposes e.g. battery current limit
> > for preventive vdrop prevention. By nature, thermal zone are sensors,
> > and cooling devices are usually components with potential high power
> > use.
> 
> [Added Greghk and Rafael in Cc]
> 
> I understand but I would like to have Greg's and Rafael's opinion on that.
> 
> The result is:
> 
> ls -al /sys/devices/virtual/thermal/
> total 0
> drwxr-xr-x 22 root root 0 Dec 10 12:34 .
> drwxr-xr-x 15 root root 0 Dec 10 12:34 ..
> drwxr-xr-x  2 root root 0 Dec 10 13:18 cdev-by-name

Ick!

> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device0
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device1
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device10
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device11
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device12
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device13
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device14
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device15
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device2
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device3
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device4
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device5
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device6
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device7
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device8
> drwxr-xr-x  3 root root 0 Dec 10 12:34 cooling_device9
> drwxr-xr-x  3 root root 0 Dec 10 12:34 thermal_zone0
> drwxr-xr-x  3 root root 0 Dec 10 12:34 thermal_zone1
> drwxr-xr-x  2 root root 0 Dec 10 13:18 tz-by-name
> 
> ls -al /sys/devices/virtual/thermal/cdev-by-name/
> total 0
> drwxr-xr-x  2 root root 0 Dec 10 13:18 .
> drwxr-xr-x 22 root root 0 Dec 10 12:34 ..
> lrwxrwxrwx  1 root root 0 Dec 10 13:18 thermal-cpufreq-0 ->
> ../cooling_device0

Ick ick ick!

What is this all for?

Where is the Documentation/ABI/ entry trying to explain this mess?
Please provide that and we can go from there as I have no idea what this
is trying to "help with".

thanks,

greg k-h