linux-kernel - Re: thermal/drivers/tegra: Getting rid of the get_thermal

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Date:   Tue, 7 Feb 2023 13:38:08 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Wei Ni <wni@...dia.com>, "Rafael J. Wysocki" <rafael@...nel.org>,
        Jon Hunter <jonathanh@...dia.com>,
        Johan Hovold <johan@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: thermal/drivers/tegra: Getting rid of the get_thermal_instance()
 usage

On 07/02/2023 13:18, Thierry Reding wrote:
> On Mon, Feb 06, 2023 at 03:50:22PM +0100, Daniel Lezcano wrote:
>>
>> Hi Thierry,
>>
>> did you have the time to look at the get_thermal_instance() removal ?
>>
>>
>> On 26/01/2023 13:55, Thierry Reding wrote:
>>
>>> 	[   12.354091] tegra_soctherm 700e2000.thermal-sensor: missing thermtrips, will use critical trips as shut down temp
>>> 	[   12.379009] tegra_soctherm 700e2000.thermal-sensor: thermtrip: will shut down when cpu reaches 102500 mC
>>> 	[   12.388882] tegra_soctherm 700e2000.thermal-sensor: programming throttle for cpu to 102500
>>> 	[   12.401007] tegra_soctherm 700e2000.thermal-sensor: throttrip: will throttle when cpu reaches 102500 mC
>>> 	[   12.471041] tegra_soctherm 700e2000.thermal-sensor: thermtrip: will shut down when gpu reaches 103000 mC
>>> 	[   12.482852] tegra_soctherm 700e2000.thermal-sensor: programming throttle for gpu to 103000
>>> 	[   12.482860] tegra_soctherm 700e2000.thermal-sensor: throttrip: will throttle when gpu reaches 103000 mC
>>> 	[   12.485357] tegra_soctherm 700e2000.thermal-sensor: thermtrip: will shut down when pll reaches 103000 mC
>>> 	[   12.501774] tegra_soctherm 700e2000.thermal-sensor: thermtrip: will shut down when mem reaches 103000 mC
>>>
>>> and after these changes, it turns into:
>>>
>>> 	[   12.447113] tegra_soctherm 700e2000.thermal-sensor: missing thermtrips, will use critical trips as shut down temp
>>> 	[   12.472300] tegra_soctherm 700e2000.thermal-sensor: thermtrip: will shut down when cpu reaches 102500 mC
>>> 	[   12.481789] tegra_soctherm 700e2000.thermal-sensor: programming throttle for cpu to 102500
>>> 	[   12.495447] tegra_soctherm 700e2000.thermal-sensor: throttrip: will throttle when cpu reaches 102500 mC
>>> 	[   12.496514] tegra_soctherm 700e2000.thermal-sensor: thermtrip: will shut down when gpu reaches 103000 mC
>>> 	[   12.510353] tegra_soctherm 700e2000.thermal-sensor: programming throttle for gpu to 103000
>>> 	[   12.526856] tegra_soctherm 700e2000.thermal-sensor: throttrip: will throttle when gpu reaches 103000 mC
>>> 	[   12.528774] tegra_soctherm 700e2000.thermal-sensor: thermtrip: will shut down when pll reaches 103000 mC
>>> 	[   12.569352] tegra_soctherm 700e2000.thermal-sensor: programming throttle for pll to 103000
>>> 	[   12.577635] tegra_soctherm 700e2000.thermal-sensor: throttrip: will throttle when pll reaches 103000 mC
>>> 	[   12.590952] tegra_soctherm 700e2000.thermal-sensor: thermtrip: will shut down when mem reaches 103000 mC
>>> 	[   12.600783] tegra_soctherm 700e2000.thermal-sensor: programming throttle for mem to 103000
>>> 	[   12.609204] tegra_soctherm 700e2000.thermal-sensor: throttrip: will throttle when mem reaches 103000 mC
>>>
>>> The "programming throttle ..." messages are something I've added locally
>>> to trace what gets called. So it looks like for "pll" and "mem" thermal
>>> zones, we now program trip points whereas we previously didn't.
> 
> My diagnosis above wasn't entirely correct. We're not actually skipping
> trip point programming for PLL and MEM thermal zones in the current
> code. Instead, we skip throttle programming. As far as I can tell this
> is a mechanism built into ACTMON to allow it to automatically throttle
> when a zone reaches a certain temperature.
> 
> This is modelled as a cooling device, but internally it's actually done
> automatically, which is why we have this code that programs the throttle
> at driver probe time, rather than the on-demand programming that typical
> cooling device would do (such as a fan).
> 
> The reason why we have get_thermal_instance() here is to check if this
> built-in cooling device has been configured for the "hot" trip point. If
> not, we don't want the throttle programming to happen. This adds the
> added flexibility of explicitly disabling the automatic throttling by
> ACTMON and using another cooling device (or none at all) if that's what
> is needed.
> 
> Dropping just the call to get_thermal_instance() and relying on the
> find_throttle_cfg_by_name() function will always return a valid throttle
> configuration. This is slightly obfuscated because of this:
> 
> 	cdev = ts->throt_cfgs[i].cdev;
> 	if (get_thermal_instance(tz, cdev, trip_id))
> 		stc = find_throttle_cfg_by_name(ts, cdev->type);
> 
> As far as I can tell this will always return &ts->throt_cfgs[i], so the
> find_throttle_cfg_by_name() call is a bit redundant here. I'll look into
> fixing that.
> 
> In any case, the important thing is that it would always find a valid
> throttle configuration and therefore program the throttle, even if we
> may not want to.

Why not rely on the thermal framework mechanism to set the hwtrpis ?

thermal_zone_device_register() calls thermal_zone_device_update(). This 
one calls thermal_zone_set_trips() which programs the hardware trip point.

When we suspend/resume, the PM notifiers are calling 
thermal_zone_device_update() which in turn sets the hw trip points.

May be I'm missing something but isn't enough for the sensor ?


> Possibly we could work around that by removing this fiddly special case
> and instead add a new callback for the cooling devices that can be run
> when they are bound to a thermal zone. This would allow the throttle
> programming to be initiated from within the thermal core rather than
> "bolted on" like it is now and should allow us to achieve the same
> effect but without calling into get_thermal_instance().
> 
> I'll try and prototype this, but feel free to suggest anything better if
> you can think of something.
> 
> Thierry

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