Re: [RFC PATCH 3/4] thermal: ti-soc-thermal: use thermal DT infrastructure

From: Eduardo Valentin <eduardo.valentin@ti.com>
To: Eduardo Valentin <eduardo.valentin@ti.com>
Cc: Lucas Stach <l.stach@pengutronix.de>, linux-pm@vger.kernel.org
Subject: Re: [RFC PATCH 3/4] thermal: ti-soc-thermal: use thermal DT infrastructure
Date: Mon, 15 Jul 2013 09:38:42 -0400	[thread overview]
Message-ID: <51E3FB62.1070106@ti.com> (raw)
In-Reply-To: <51E3FAE7.3090609@ti.com>

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On 15-07-2013 09:36, Eduardo Valentin wrote:
> On 15-07-2013 09:25, Eduardo Valentin wrote:
>> On 15-07-2013 08:59, Lucas Stach wrote:
>>> Am Montag, den 15.07.2013, 08:33 -0400 schrieb Eduardo Valentin:
>>>> On 15-07-2013 08:12, Lucas Stach wrote:
>>>>> Hi Eduardo and others,
>>>>>
>>>>> Eduardo Valentin <eduardo.valentin <at> ti.com> writes:
>>>>>
>>>>>>
>>>>>> This patch improves the ti-soc-thermal driver by adding the
>>>>>> support to build the thermal zones based on DT nodes.
>>>>>>
>>>>>> The driver will have two options now to build the thermal
>>>>>> zones. The first option is the zones originally coded
>>>>>> in this driver. So, the driver behavior will be same
>>>>>> if there is no DT node describing the zones. The second
>>>>>> option, when it is found a DT node with thermal data,
>>>>>> will used the common infrastructure to build the thermal
>>>>>> zone and bind its cooling devices.
>>>>>>
>>>>>> In either case, this driver still adds to the system
>>>>>> a cpufreq cooling device.
>>>>>>
>>>>>
>>>>> I really like the idea to configure thermal zones using devicetree, it's a
>>>>> step in the right direction. We might follow suit with the i.MX6 tempmon
>>>>> driver to use this infrastructure.
>>>>>
>>>>> What I strongly dislike is the notion of the sensor drivers instantiating
>>>>> the cooling devices and the resulting devicetree binding. This seems really
>>>>> backward to me.
>>>>> I would rather see the drivers associated with the cooling devices (like
>>>>> cpufreq and the respective gpu drivers) to instantiate the cooling devices
>>>>> and the thermal zone referring to them through phandles. I think it
>>>>> shouldn't be too much work to go in that direction.
>>>>> The current method might be enough to work with the current thermal platform
>>>>> drivers, but if you want to go down the route to eventually use plain i2c
>>>>> devices (likely with an existing hwmon driver) you have to get away from the
>>>>> sensor devices instantiating the cooling devices.
>>>>
>>>> I agree with you. While implementing the RFC, it looks awkward that the
>>>> ti-soc-thermal driver had to do the job to load the cpufreq-cooling
>>>> device. Problem is that a cooling device is not really a real device,
>>>> and might get flamed while represented as a device tree node.
>>>>
>>> I don't think we even need to represent this into the device tree. We
>>> already have the CPU nodes there and the cpu-freq driver is already
>>> linked to those. It should be easy to have a global list of registered
>>> thermal devices in the thermal framework together with their associated
>>> devices, so one could look up cooling devices through the thermal
>>> framework when we only have a phandle to the cpu node.
>>
>> Well, we do have a list of thermal cooling devices associated with its
>> corresponding struct device. That is private data to the thermal
>> framework. However, one needs to load the cooling device in order to its
>> data structure appear in this list. The framework can not be proactive
>> here. Some other entity needs to see the need and inform the thermal
>> framework of it.
>>
> 
> 
> 
> as simple as the following:
> diff --git a/drivers/cpufreq/cpufreq-cpu0.c b/drivers/cpufreq/cpufreq-cpu0.c
> index 3ab8294..486881c 100644
> --- a/drivers/cpufreq/cpufreq-cpu0.c
> +++ b/drivers/cpufreq/cpufreq-cpu0.c
> @@ -20,6 +20,9 @@
>  #include <linux/platform_device.h>
>  #include <linux/regulator/consumer.h>
>  #include <linux/slab.h>
> +#include <linux/thermal.h>
> +#include <linux/cpu_cooling.h>
> +#include <linux/cpumask.h>
> 
>  static unsigned int transition_latency;
>  static unsigned int voltage_tolerance; /* in percentage */
> @@ -28,6 +31,7 @@ static struct device *cpu_dev;
>  static struct clk *cpu_clk;
>  static struct regulator *cpu_reg;
>  static struct cpufreq_frequency_table *freq_table;
> +static struct thermal_cooling_device *cdev;
> 
>  static int cpu0_verify_speed(struct cpufreq_policy *policy)
>  {
> @@ -256,6 +260,9 @@ static int cpu0_cpufreq_probe(struct platform_device
> *pdev)
>                 goto out_free_table;
>         }
> 
> +       if (!of_property_read_bool(np, "needs-cooling"))

This is obviously supposed to be

 +       if (of_property_read_bool(np, "needs-cooling"))

> +               cdev = cpufreq_cooling_register(cpu_present_mask);
> +
>         of_node_put(np);
>         of_node_put(parent);
>         return 0;
> @@ -269,6 +276,7 @@ out_put_node:
> 
>  static int cpu0_cpufreq_remove(struct platform_device *pdev)
>  {
> +       cpufreq_cooling_unregister(cdev);
>         cpufreq_unregister_driver(&cpu0_cpufreq_driver);
>         opp_free_cpufreq_table(cpu_dev, &freq_table);
> 
>> For instance, assuming that all systems will need a cpufreq cooling
>> device is a flaw, because that is not the case. Thus, it makes sense to
>> have a property, say at the cpu node, to determine that it needs
>> cooling. However, that won't be saying how it would cool off.
> 
> 
> Then you would define your cpu0 node as:
> 
> 		cpu@0 {
> 			/* OMAP443x variants OPP50-OPPNT */
> 			operating-points = <
> 				/* kHz    uV */
> 				300000  1025000
> 				600000  1200000
> 				800000  1313000
> 				1008000 1375000
> 			>;
> 			clock-latency = <300000>; /* From legacy driver */
> 			needs-cooling; /* make sure we have cpufreq-cooling */
> 		};
> 
> Because in that system we actually need to take care of the cpu thermal.
> 
> 
>>
>>
>>>
>>>> I could try to push something following the same idea as the one I am
>>>> trying to sell with this series for sensor devices. For instance, in a
>>>> sensor node I am attaching a phandle to describe how thermal fw must
>>>> behave. Then the sensor driver it is supposed to load the thermal data
>>>> into the thermal fw. Same could apply for instance for cpufreq cooling
>>>> device. at the cpu node we could have a 'cooling_device' node at the cpu
>>>> node, while loading cpufreq-cpu0.
>>>
>>> I think a separate cooling_device node may be only necessary if we stuff
>>> additional info in there. If it's just a plain cooling device I think it
>>> is reasonable for the cpufreq driver to just register a cooling device
>>> if the thermal framework is there.
>>
>> no, I think this is not what we want, because, as I said, not all cpus
>> will need cooling. Just because the thermal framework is there does not
>> mean your cpu needs cooling. As you can see, the thermal framework is
>> not only for cpu cooling. It can be used for any other thermal need.
>> Besides one needs to cover for the case where you are building for
>> multiple platform support. Assuming system needs based on Kconfig setup
>> is not very likely to scale in this case.
>>
>>>
>>> I would really like the information about a thermal zone to hang off one
>>> dt node rather than being scattered over several nodes. This way it may
>>
>> Again, thermal framework is not about only cpu(freq) cooling. Thermal
>> zone info can (and will) be hanged off in one dt node. But please don't
>> mix concepts. Just because a cooling device is part of a thermal zone,
>> it does not mean it is only used there and that it can be defined there.
>> One can use a cooling device in different thermal zones.
>>
>>> be easy to reference a cooling device in different thermal zones with
>>> different weight, etc. As long as we define a thermal zone to always be
>>> defined by a single sensor the right place seems to be the proposed
>>> subnode to the sensor. If we want a zone to have more than one sensor,
>>> we might even want a separate dt node for the thermal zone, referencing
>>> both sensors and cooling devices through phandles.
>>
>> I still don't get why and how defining a thermal zone inside a sensor
>> phandle can prevent us defining a cooling device in different device
>> phandle.
> 
> 
> Then you can keep everything about your thermal zone in one single
> phandle, as follows, but remember, this is is the info about the thermal
> zone, not about a cooling device. For instance, that is the zone built
> on top of a bandgap sensor:
> 	bandgap {
> 		reg = <0x4a002260 0x4 0x4a00232C 0x4>;
> 		compatible = "ti,omap4430-bandgap";
> 		thermal_zone {
> 			type = "CPU";
> 			mask = <0x03>; /* trips writability */
> 			passive_delay = <250>; /* milliseconds */
> 			polling_delay = <1000>; /* milliseconds */
> 			governor = "step_wise";
> 			trips {
> 				alert@100000{
> 					temperature = <100000>;
> 					hysteresis = <0>;
> 					type = <1>;
> 				};
> 				crit@125000{
> 					temperature = <125000>;
> 					hysteresis = <0>;
> 					type = <3>;
> 				};
> 			};
> 			bind_params {
> 				action@0{
> 					cooling_device = "thermal-cpufreq";
> 					weight = <100>; /* percentage */
> 					mask = <0x01>;
> 				};
> 			};
> 		};
> 	};
> 
> 
> And you see that, in this case, the bandgap sensor driver does not need
> to worry about loading the cpufreq cooling device anymore. Who is
> responsible of doing that is the cpufreq driver, with the above
> proposal, when it makes sense and when there is a need.
> 
> 
> 
>>
>>>
>>> Regards,
>>> Lucas
>>>
>>
>>
> 
> 


-- 
You have got to be excited about what you are doing. (L. Lamport)

Eduardo Valentin


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