Re: [PATCHv9 02/20] thermal: introduce device tree parser

Wei Ni
2014-01-14T02:54:04Z

On 01/14/2014 05:29 AM, Eduardo Valentin wrote:
> * PGP Signed by an unknown key
>
> Wei,
>
> On 06-01-2014 22:44, Wei Ni wrote:
>> On 01/06/2014 10:54 PM, Eduardo Valentin wrote:
>>>> Old Signed by an unknown key
>>>
>>> On 06-01-2014 09:51, Mark Rutland wrote:
>>>> On Thu, Jan 02, 2014 at 05:50:06PM +0000, Matthew Longnecker wrote:
>>>>>
>>>>>> I think the platform driver may set governor for the thermal zone,
>>>>>> so how about to add a property named as "governor",
>>>>>> and parse it to tzp->governor_name,
>>>>>> something like:
>>>>>> ret = of_property_read_string(child, "governor", &str);
>>>>>> if (ret == 0)
>>>>>> if (strlen(str) < THERMAL_NAME_LENGTH)
>>>>>> strcpy(tzp->governor_name, str);
>>>>>>
>>>>>> Thanks.
>>>>>> Wei.
>>>>>
>>>>> DT is supposed to describe the hardware, right? The governor isn't
>>>>> hardware -- it's a software control policy. On the other hand, that
>>>>> control policy must be tuned according to the behaviors of the platform
>>>>> hardware otherwise the system will be unstable.
>>>>>
>>>>> Is it appropriate to be naming the governor in DT? If so, is it equally
>>>>> appropriate to describe any governor-specific parameters in DT (even
>>>>> though they are pure software constructs)?
>>>>
>>>> The dt should be relatively static -- if the hardware doesn't change the
>>>> dt shouldn't have to.
>>>>
>>>> The governers are not static. We can introduce new ones and throw away
>>>> old ones at any time. Tuning parameters can also change at any time.
>>>>
>>>> I'd prefer to not have governer details described in the dt, and the
>>>> choice of governer and configuration of its tuning parameters should be
>>>> made at runtime somehow.
>>>
>>> Agreed.
>>
>> Yes, I think so, but the of-thermal driver handle the
>> thermal_zone_device_register, and pass the "tzp" without governor_name,
>
> In fact, it will fall into the default governor, which is step_wise, by
> default config.

In the thermal_zone_device_register(), it has following codes:
if (tz->tzp)
tz->governor = __find_governor(tz->tzp->governor_name);
else
tz->governor = __find_governor(DEFAULT_THERMAL_GOVERNOR);

It mean if the tz->tzp is not NULL, and the governor_name is NULL, then
the __find_governor() will return NULL, so the tz->governor is NULL, it
can't fall into the default governor. And in the of-thermal driver, it
call the thermal_zone_device_register(), and pass the "tzp" without
governor_name.
I think if we want to change the governor in user space, we need to fix
this first.

>
>> so the created thermal_zone's governor will be NULL, then it can't run
>> into the governor->throttle() if needed. And currently there have no
>
> Actually, no, the tz will be set to default governor, and its throttle
> call will be called.
>
>> interface to support updating governor and configuration at runtime.
>> I think it's better to initialize the governor_name when register the
>> thermal zone device in the of-thermal driver.
>
> Still, why would you need to change the governor from a in kernel
> decision? There is an ABI to change the thermal zone policy based on
> user(land) request. If you need to change the policy from within the
> kernel, which seams to be what you are trying to propose, you need to
> explain why you need it, say, by giving at least one user of this API or
> explaining its use case.

The thermal_zone_device_register() support to set the governor which you
want, but with the of-thermal framework, it only support to set to
default governor, if fix above issue. I think the driver which use the
of-thermal should be able to set to any governors which it want, in its
initialization. So I add the function thermal_update_governor().

>
>>
>> Thanks.
>>
>>>
>>>>
>>>> Thanks,
>>>> Mark.
>>>>
>>>>
>>>
>>>
>>
>>
>>
>
>