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SubjectRe: [PATCH v3 0/3] thermal: introduce by-name softlink
On Sun, Dec 15, 2019 at 8:34 AM Sandeep Patil <sspatil@android.com> wrote:
>
> 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?
>
Parsing can be done in clients, one particular place is for init, but
still possible.
https://cs.android.com/search?q=tz-by-name%20file:%5C.rc
Yeah, as said, we can definitely do pasing in every userspace daemon,
but AFAICT, all userspace codes (open source / closed source) are
using thermal zones / cooling devices by "name/type". So I am
probling the possibility of having this kind of support for
convenience.
FYI, Chrome also feel this is useful
https://lore.kernel.org/lkml/20191206191545.GO228856@google.com/

> 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?
>
Those mapping are usually static nowadays, but could be changed if
modules are unloaded. Right now we only do UEVENT for userspace
governor,
https://github.com/torvalds/linux/blob/9c7db5004280767566e91a33445bf93aa479ef02/drivers/thermal/user_space.c#L37
Actually, I am about sending another RFC to add some more uevent to
userspace. Without the UEVENT, I think we cannot guarantee the mapping
is static.

> >
> > >
> > > 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)
>
I replied above before reading this part, and I guess we had the same
thought on 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
> > >
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> > > <http://twitter.com/#!/linaroorg> Twitter |
> > > <http://www.linaro.org/linaro-blog/> Blog
> > >

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