linux-kernel - Re: [linux-pm] [RFC 1/4] cpuidle: define the enter function in the driver structure

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Date:	Fri, 08 Jun 2012 23:03:06 +0530
From:	Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
CC:	lenb@...nel.org, linux-acpi@...r.kernel.org,
	linux-pm@...ts.linux-foundation.org, linaro-dev@...ts.linaro.org,
	linux-kernel@...r.kernel.org
Subject: Re: [linux-pm] [RFC 1/4] cpuidle: define the enter function in the
 driver structure

Hi Daniel,

On 06/08/2012 09:32 PM, Daniel Lezcano wrote:

> We have the state index passed as parameter to the 'enter' function.
> Most of the drivers assign their 'enter' functions several times in
> the cpuidle_state structure, as we have the index, we can delegate
> to the driver to handle their own callback array.
> 
> That will have the benefit of removing multiple lines of code in the
> different drivers.
> 
> In order to smoothly modify the driver, the 'enter' function are in
> the driver structure and in the cpuidle state structure. That will
> let the time to modify the different drivers one by one.
> So the 'cpuidle_enter' function checks if the 'enter' callback is
> assigned in the driver structure and use it, otherwise it invokes
> the 'enter' assigned to the cpuidle_state.


Currently, the backend driver initializes
all the cpuidle states supported on the platform,
and each state can have its own enter routine
which can be unique  This is a clean approach.

By moving the enter routine into the driver,
we are enforcing in having only one enter state.
There is unnecessary overhead involved
in calling a wrapper routine just to
index into the right idle state routine
for many platforms at runtime.


> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>  drivers/cpuidle/cpuidle.c |    4 +++-
>  include/linux/cpuidle.h   |    1 +
>  2 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index d90519c..155dee7 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -46,7 +46,9 @@ static inline int cpuidle_enter(struct cpuidle_device *dev,
>  				struct cpuidle_driver *drv, int index)
>  {
>  	struct cpuidle_state *target_state = &drv->states[index];
> -	return target_state->enter(dev, drv, index);
> +
> +	return drv->enter(dev, drv, index) ? drv->enter(dev, drv, index) :
> +		target_state->enter(dev, drv, index);
>  }
> 
>  static inline int cpuidle_enter_tk(struct cpuidle_device *dev,
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index 6c26a3d..d82e169 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -130,6 +130,7 @@ struct cpuidle_driver {
>  	struct cpuidle_state	states[CPUIDLE_STATE_MAX];
>  	int			state_count;
>  	int			safe_state_index;
> +	int (*enter)(struct cpuidle_device *, struct cpuidle_driver *, int);
>  };
> 
>  #ifdef CONFIG_CPU_IDLE


Cheers,
Deepthi

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