linux-kernel - Re: [PATCH V3 7/8] ARM: cpuidle: Register per cpuidle device

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Date:	Sat, 21 Mar 2015 20:35:47 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"robherring2@...il.com" <robherring2@...il.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"lina.iyer@...aro.org" <lina.iyer@...aro.org>,
	"sboyd@...eaurora.org" <sboyd@...eaurora.org>
Subject: Re: [PATCH V3 7/8] ARM: cpuidle: Register per cpuidle device

On Fri, Mar 20, 2015 at 11:44:00AM +0000, Daniel Lezcano wrote:
> Some architectures have some cpus which does not support idle states.
> 
> Let the underlying low level code to return -ENXIO when it is not
> possible to set an idle state.

Well, this is getting interesting. We are parsing possible CPUs to
detect if they have common idle states in DT. If a CPU does not support
idle states, the cpu node for that CPU should not define any idle
state.

The approach above will work with my heterogenous system patch, since
the respective CPUidle driver mask will be created by parsing the DT
idle states.

http://www.spinics.net/lists/arm-kernel/msg403190.html

In current approach if a "possible " CPU does not have idle states, we do
not init CPUidle at all.

So, to cut a long story short, what does "a cpu does not support idle
states" mean ?

Does it mean that firmware defines idle states for that CPU in DT but
initializing them fail ?

I am fine with this patch, but we need to define -ENXIO return properly.

> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>  drivers/cpuidle/cpuidle-arm.c | 42 ++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle-arm.c b/drivers/cpuidle/cpuidle-arm.c
> index 1c94b88..e4a6eba 100644
> --- a/drivers/cpuidle/cpuidle-arm.c
> +++ b/drivers/cpuidle/cpuidle-arm.c
> @@ -17,6 +17,7 @@
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> +#include <linux/slab.h>
>  
>  #include <asm/cpuidle.h>
>  
> @@ -94,6 +95,7 @@ static int __init arm_idle_init(void)
>  {
>  	int cpu, ret;
>  	struct cpuidle_driver *drv = &arm_idle_driver;
> +	struct cpuidle_device *dev;
>  
>  	/*
>  	 * Initialize idle states data, starting at index 1.
> @@ -105,18 +107,54 @@ static int __init arm_idle_init(void)
>  	if (ret <= 0)
>  		return ret ? : -ENODEV;
>  
> +	ret = cpuidle_register_driver(drv);
> +	if (ret) {
> +		pr_err("Failed to register cpuidle driver\n");
> +		return ret;
> +	}
> +
>  	/*
>  	 * Call arch CPU operations in order to initialize
>  	 * idle states suspend back-end specific data
>  	 */
>  	for_each_possible_cpu(cpu) {
>  		ret = arm_cpuidle_init(cpu);
> +
> +		/* This cpu does not support any idle states */

We need to define what this means. If it means a cpu with no idle
states in its cpu node the parsing would not even get here since
to init the driver all possible cpus have to have the *same* idle states to
function at present.

Lorenzo

> +		if (ret == -ENXIO)
> +			continue;
> +
>  		if (ret) {
>  			pr_err("CPU %d failed to init idle CPU ops\n", cpu);
> -			return ret;
> +			goto out_fail;
> +		}
> +
> +		dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> +		if (!dev) {
> +			pr_err("Failed to allocate cpuidle device\n");
> +			goto out_fail;
> +		}
> +		dev->cpu = cpu;
> +
> +		ret = cpuidle_register_device(dev);
> +		if (ret) {
> +			pr_err("Failed to register cpuidle device for CPU %d\n",
> +			       cpu);
> +			kfree(dev);
> +			goto out_fail;
>  		}
>  	}
>  
> -	return cpuidle_register(drv, NULL);
> +	return 0;
> +out_fail:
> +	while (--cpu >= 0) {
> +		dev = per_cpu(cpuidle_devices, cpu);
> +		cpuidle_unregister_device(dev);
> +		kfree(dev);
> +	}
> +
> +	cpuidle_unregister_driver(drv);
> +
> +	return ret;
>  }
>  device_initcall(arm_idle_init);
> -- 
> 1.9.1
> 
> 
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