Date:	Tue, 23 Oct 2012 16:23:43 +0800
From:	Hongbo Zhang <hongbo.zhang@...aro.org>
To:	Francesco Lavra <francescolavra.fl@...il.com>
Cc:	linaro-dev@...ts.linaro.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, STEricsson_nomadik_linux@...t.st.com,
	kernel@...oocommunity.org, linaro-kernel@...ts.linaro.org,
	"hongbo.zhang" <hongbo.zhang@...aro.com>, patches@...aro.org,
	amit.kachhap@...aro.org
Subject: Re: [PATCH 1/5] Thermal: do bind operation after thermal zone or
 cooling device register returns.

Hi Francesco,
I found out more points about this issue.

[1]
cdev should be ready when get_max_state callback be called, otherwise
parameter cdev is useless, imagine there may be cases that
get_max_state call back is shared by more than one cooling devices of
same kind, like this:
common_get_max_state(*cdev, *state)
{
    if (cdev == cdev1)  *state = 3;
    else if (cdev == cdev)  *state = 5;
    else
}

[2]
In my cpufreq cooling case(in fact cdev is not used to calculate
max_state), the cooling_cpufreq_list should be ready when
get_max_state call back is called. In this patch I defer the binding
when registration finished, but this is not perfect now, see this
routine in cpufreq_cooling_register:

thermal_cooling_device_register;
at this time: thermal_bind_work -> get_max_state -> get NULL
cooling_cpufreq_list
and then: list_add_tail(&cpufreq_dev->node, &cooling_cpufreq_list)
This is due to we cannot know exactly when the bind work is executed.
(and this can be fixed by moving mutex_lock(&cooling_cpufreq_lock)
aheadof thermal_cooling_device_register and other corresponding
modifications, but I found another way as below)

[3]
Root cause of this problem is calling get_max_state in register -> bind routine.
Better solution is to add another parameter in cooling device register
function, also add a max_state member in struct cdev, like:
thermal_cooling_device_register(char *type, void *devdata, const
struct thermal_cooling_device_ops *ops, unsigned long max_state)
and then in the bind function:
if(cdev->max_state)
    max_state = cdev->max_state;
else
    cdev->get_max_state(cdev, &max_state)

It is common sense that the cooling driver should know its cooling
max_state(ability) before registration, and it can be offered when
register.
I think this way doesn't change both thermal and cooling layer much,
it is more clear.
I will update this patch soon.


On 21 October 2012 18:05, Francesco Lavra <francescolavra.fl@...il.com> wrote:
> Hi,
>
> On 10/16/2012 01:44 PM, hongbo.zhang wrote:
>> From: "hongbo.zhang" <hongbo.zhang@...aro.com>
>>
>> In the previous bind function, cdev->get_max_state(cdev, &max_state) is called
>> before the registration function finishes, but at this moment, the parameter
>> cdev at thermal driver layer isn't ready--it will get ready only after its
>> registration, so the the get_max_state callback cannot tell the max_state
>> according to the cdev input.
>> This problem can be fixed by separating the bind operation out of registration
>> and doing it when registration completely finished.
>
> When thermal_cooling_device_register() is called, the thermal framework
> assumes the cooling device is "ready", i.e. all of its ops callbacks
> return meaningful results. If the cooling device is not ready at this
> point, then this is a bug in the code that registers it.
> Specifically, the faulty code in your case is in the cpufreq cooling
> implementation, where the cooling device is registered before being
> added to the internal list of cpufreq cooling devices. So, IMHO the fix
> is needed there.
>
> --
> Francesco
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