linux-kernel - Re: [PATCH v3 2/3] ARM: imx: Add imx5 cpuidle driver

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Date:	Wed, 9 May 2012 10:02:14 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Robert Lee <rob.lee@...aro.org>
Cc:	kernel@...gutronix.de, shawn.guo@...aro.org,
	amit.kucheria@...aro.org, daniel.lezcano@...aro.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linaro-dev@...ts.linaro.org, patches@...aro.org, jj@...osbits.net
Subject: Re: [PATCH v3 2/3] ARM: imx: Add imx5 cpuidle driver

On Mon, May 07, 2012 at 04:16:46PM -0500, Robert Lee wrote:
> Add imx5 cpuidle driver.
> 
> Signed-off-by: Robert Lee <rob.lee@...aro.org>
> ---
>  arch/arm/mach-imx/mm-imx5.c |   42 +++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 39 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/mach-imx/mm-imx5.c b/arch/arm/mach-imx/mm-imx5.c
> index d6b7e9f..0b3a4cc 100644
> --- a/arch/arm/mach-imx/mm-imx5.c
> +++ b/arch/arm/mach-imx/mm-imx5.c
> @@ -20,26 +20,61 @@
>  
>  #include <mach/hardware.h>
>  #include <mach/common.h>
> +#include <mach/cpuidle.h>
>  #include <mach/devices-common.h>
>  #include <mach/iomux-v3.h>
>  
>  static struct clk *gpc_dvfs_clk;
>  
> -static void imx5_idle(void)
> +static int imx5_idle(void)
>  {
> +	int ret = 0;
> +
>  	/* gpc clock is needed for SRPG */
>  	if (gpc_dvfs_clk == NULL) {
>  		gpc_dvfs_clk = clk_get(NULL, "gpc_dvfs");

This clk_get should go away here and be moved somewhere to
initialization. Also, if getting this clock fails we can still
do regular cpu_do_idle. Additionally, if clk_get fails, we'll
have a ERR_PTR value in gpc_dvfs_clk in which case the
gpc_dvfs_clk == NULL won't trigger next time you are here and
then you'll enable a nonexisting clock below.

>  		if (IS_ERR(gpc_dvfs_clk))
> -			return;
> +			return -ENODEV;
>  	}
>  	clk_enable(gpc_dvfs_clk);
>  	mx5_cpu_lp_set(WAIT_UNCLOCKED_POWER_OFF);
>  	if (!tzic_enable_wake())
>  		cpu_do_idle();
> +	else
> +		ret = -EBUSY;
>  	clk_disable(gpc_dvfs_clk);
> +
> +	return ret;
> +}
> +
> +static int imx5_cpuidle_enter(struct cpuidle_device *dev,
> +				struct cpuidle_driver *drv, int idx)
> +{
> +	int ret;
> +
> +	ret = imx5_idle();
> +
> +	if (ret < 0)
> +		return ret;
> +
> +	return idx;
>  }
>  
> +static struct cpuidle_driver imx5_cpuidle_driver = {
> +	.name			= "imx5_cpuidle",
> +	.owner			= THIS_MODULE,
> +	.en_core_tk_irqen	= 1,
> +	.states[0]	= {
> +		.enter			= imx5_cpuidle_enter,
> +		.exit_latency		= 20, /* max latency at 160MHz */
> +		.target_residency	= 1,
> +		.flags			= CPUIDLE_FLAG_TIME_VALID,
> +		.name			= "IMX5 SRPG",
> +		.desc			= "CPU state retained,powered off",
> +	},

I wonder why you don't add the default ARM_CPUIDLE_WFI_STATE_PWR state.
The above is something different, right? It has a greater exit latency
than ARM_CPUIDLE_WFI_STATE_PWR, so why don't we add it here aswell?

> +	.state_count		= 1,
> +};
> +
>  /*
>   * Define the MX50 memory map.
>   */
> @@ -103,7 +138,7 @@ void __init imx51_init_early(void)
>  	mxc_set_cpu_type(MXC_CPU_MX51);
>  	mxc_iomux_v3_init(MX51_IO_ADDRESS(MX51_IOMUXC_BASE_ADDR));
>  	mxc_arch_reset_init(MX51_IO_ADDRESS(MX51_WDOG1_BASE_ADDR));
> -	arm_pm_idle = imx5_idle;
> +	arm_pm_idle = (void (*)(void))imx5_idle;

Still this looks suspicious. Reading this will lead to the question why
this prototype is casted. Please just add a imx5_pm_idle with the
correct prototype.

>  }
>  
>  void __init imx53_init_early(void)
> @@ -238,4 +273,5 @@ void __init imx53_soc_init(void)
>  void __init imx51_init_late(void)
>  {
>  	mx51_neon_fixup();
> +	imx_cpuidle_init(&imx5_cpuidle_driver);
>  }
> -- 
> 1.7.10
> 
> 

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