Re: [PATCH v5 0/3] Thermal ACPI APIs for generic trip points

From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: srinivas pandruvada <srinivas.pandruvada@linux.intel.com>,
	"Zhang, Rui" <rui.zhang@intel.com>,
	"rafael@kernel.org" <rafael@kernel.org>
Cc: "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"christophe.jaillet@wanadoo.fr" <christophe.jaillet@wanadoo.fr>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>
Subject: Re: [PATCH v5 0/3] Thermal ACPI APIs for generic trip points
Date: Wed, 18 Jan 2023 23:14:22 +0100	[thread overview]
Message-ID: <d6f71181-1de4-7937-eda0-8805d9dfc3b4@linaro.org> (raw)
In-Reply-To: <340f3ecdaddb2c422dcbe3df712a082f333eab0d.camel@linux.intel.com>

On 18/01/2023 22:16, srinivas pandruvada wrote:
> On Wed, 2023-01-18 at 22:01 +0100, Daniel Lezcano wrote:
>> On 18/01/2023 21:53, srinivas pandruvada wrote:
>>> On Wed, 2023-01-18 at 21:00 +0100, Daniel Lezcano wrote:
>>>> On 18/01/2023 20:16, srinivas pandruvada wrote:
>>>>
>>>> [ ... ]
>>>>
>>>>>>> But we'd better wait for the thermald test result from
>>>>>>> Srinvias.
>>>>>>
>>>>>> A quick test show that things still work with thermald and
>>>>>> these
>>>>>> changes.
>>>>>
>>>>> But I have a question. In some devices trip point temperature
>>>>> is
>>>>> not
>>>>> static. When hardware changes, we get notification. For example
>>>>> INT3403_PERF_TRIP_POINT_CHANGED for INT3403 drivers.
>>>>> Currently get_trip can get the latest changed value. But if we
>>>>> preregister, we need some mechanism to update them.
>>>>
>>>> When the notification INT3403_PERF_TRIP_POINT_CHANGED happens, we
>>>> call
>>>> int340x_thermal_read_trips() which in turn updates the trip
>>>> points.
>>>>
>>>
>>> Not sure how we handle concurrency here when driver can freely
>>> update
>>> trips while thermal core is using trips.
>>
>> Don't we have the same race without this patch ? The thermal core can
>> call get_trip_temp() while there is an update, no ?
> Yes it is. But I can add a mutex locally here to solve.
> But not any longer.
> 
> I think you need some thermal_zone_read_lock/unlock() in core, which
> can use rcu. Even mutex is fine as there will be no contention as
> updates to trips will be rare.

I was planning to provide a thermal_trips_update(tz, trips) and from 
there handle the locking.

As the race was already existing, can we postpone this change after the 
generic trip points changes?

There is still a lot of work to do to consolidate the code. One of them 
is to provide a generic function to browse the trip points and ensure 
the code is using it instead of directly inspect the thermal zone 
internals structure.

I'm almost there but I need the remaining Intel drivers changes to be 
merged (as well as ACPI which is finished but depending on this series).

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