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SubjectRe: [PATCH v3 0/3] thermal: introduce by-name softlink
Hi Wei,

(resending because I accidentally replied only to you. Also adding everyone
else back in the thread, not sure what happened before).

On Wed, Dec 11, 2019 at 02:19:03PM -0800, Wei Wang wrote:
> On Wed, Dec 11, 2019 at 1:11 PM Daniel Lezcano
> <daniel.lezcano@linaro.org> wrote:
> >
> > On 11/12/2019 21:11, Wei Wang wrote:
> > > On Wed, Dec 11, 2019 at 12:54 AM Greg Kroah-Hartman
> > > <gregkh@linuxfoundation.org> wrote:
> > >>
> > >> 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@linaro.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.
> > >>
> > >> tree traversal is supposed to be done in userspace code :)
> > >>
> > > Yes, that can be done in userspace, but given the amount of thermal
> > > zones we have in some mobile devices, this will bring a lot of
> > > convenience.
> >
> > But usually all these thermal zones are fixed and building the name<->tz
> > association is just a question of a few lines of code from userspace,
> > no? What would be the benefit of adding more ABI?
>
>
> code reuse as tz mapping is per device tree setup and we try to use
> the same _type_ in thermal zone in shared client code for Android
> thermal API.

CMIIW, but the tz mapping today can still be done by parsing through the
directory the other way? (i.e. tz->type) instead of type->tz?

Also, I understand the resistance to add a new ABI since it will have to be
kept around forever. What would be worth knowing is if these mappings are
static (built once) or you have to go through and parse the directories every
time? AFAIU, the parsing (map creation) seems to only happen once during
boot, so we (Android) should be ok?

>
> >
> > If there is a thermal zone change, then a notification can be used, so
> > the userspace code rebuild the name<->tz, no?
>
>
> Assuming you meant for type<->tz, this mapping won't change in runtime
> in our case (not unloading things), but it could be changed due to
> device tree change, e.g. adding/removing thermal zones.

I actually think we might need this after all. This assumes all tz devices
are registered when userspace (thermal hal/daemon) is coming up. However,
that may soon not be the case and we have to adjust for devices being added
in parallel with userspace?

So, may be we need to start monitoring uevents like we do for power supplies
too? In that case, the mapping can also be done dynamically.

Lastly, I think we can make a case further if there are benefits we can share
here other than convenience. Like startup time, handing hardware variations
etc? (Also point to the current userspace code that uses this)

- ssp
>
>
> >
> > > e.g. this is on Pixel 4 XL:
> > > coral:/ # ls /sys/devices/virtual/thermal/
> > > cdev-by-name cooling_device15 cooling_device22 cooling_device3
> > > cooling_device9 thermal_zone15 thermal_zone22 thermal_zone3
> > > thermal_zone37 thermal_zone44 thermal_zone51 thermal_zone59
> > > thermal_zone66 thermal_zone73 thermal_zone80 thermal_zone88
> > > cooling_device0 cooling_device16 cooling_device23 cooling_device30
> > > thermal_zone0 thermal_zone16 thermal_zone23 thermal_zone30
> > > thermal_zone38 thermal_zone45 thermal_zone52 thermal_zone6
> > > thermal_zone67 thermal_zone74 thermal_zone81 thermal_zone9
> > > cooling_device1 cooling_device17 cooling_device24 cooling_device31
> > > thermal_zone1 thermal_zone17 thermal_zone24 thermal_zone31
> > > thermal_zone39 thermal_zone46 thermal_zone53 thermal_zone60
> > > thermal_zone68 thermal_zone75 thermal_zone82 tz-by-name
> > > cooling_device10 cooling_device18 cooling_device25 cooling_device4
> > > thermal_zone10 thermal_zone18 thermal_zone25 thermal_zone32
> > > thermal_zone4 thermal_zone47 thermal_zone54 thermal_zone61
> > > thermal_zone69 thermal_zone76 thermal_zone83
> > > cooling_device11 cooling_device19 cooling_device26 cooling_device5
> > > thermal_zone11 thermal_zone19 thermal_zone26 thermal_zone33
> > > thermal_zone40 thermal_zone48 thermal_zone55 thermal_zone62
> > > thermal_zone7 thermal_zone77 thermal_zone84
> > > cooling_device12 cooling_device2 cooling_device27 cooling_device6
> > > thermal_zone12 thermal_zone2 thermal_zone27 thermal_zone34
> > > thermal_zone41 thermal_zone49 thermal_zone56 thermal_zone63
> > > thermal_zone70 thermal_zone78 thermal_zone85
> > > cooling_device13 cooling_device20 cooling_device28 cooling_device7
> > > thermal_zone13 thermal_zone20 thermal_zone28 thermal_zone35
> > > thermal_zone42 thermal_zone5 thermal_zone57 thermal_zone64
> > > thermal_zone71 thermal_zone79 thermal_zone86
> > > cooling_device14 cooling_device21 cooling_device29 cooling_device8
> > > thermal_zone14 thermal_zone21 thermal_zone29 thermal_zone36
> > > thermal_zone43 thermal_zone50 thermal_zone58 thermal_zone65
> > > thermal_zone72 thermal_zone8 thermal_zone87
> > >
> > >
> > >> But what userspace code needs to do this, and for what?
> > > In Android, thermal daemon and thermal HAL as well as some init.rc
> > > script would use those thermal paths for managing and monitoring
> > > thermal. The daemon/HAL could have logic pipled in, however Android's
> > > init.rc script would be really tricky.
> > > On a related note, we also create /dev/block/by-name links from userspace.
> > >
> > > Thanks!
> > > -Wei
> > >>
> > >> thanks,
> > >>
> > >> greg k-h
> >
> >
> > --
> > <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
> >
> > Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
> > <http://twitter.com/#!/linaroorg> Twitter |
> > <http://www.linaro.org/linaro-blog/> Blog
> >

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