linux-kernel - Re: [PATCH 1/3] ARM: imx: Add common imx cpuidle init functionality.

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Message-ID: <CAMXH7KH41kWMPu_dEpetZc8OUD3C0-mtxGbXX0Vqd4EODPWJUg@mail.gmail.com>
Date:	Tue, 17 Apr 2012 08:54:03 -0500
From:	Rob Lee <rob.lee@...aro.org>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	kernel@...gutronix.de, linaro-dev@...ts.linaro.org,
	patches@...aro.org, daniel.lezcano@...aro.org,
	linux-kernel@...r.kernel.org, amit.kucheria@...aro.org,
	shawn.guo@...aro.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] ARM: imx: Add common imx cpuidle init functionality.

On Tue, Apr 17, 2012 at 2:43 AM, Sascha Hauer <s.hauer@...gutronix.de> wrote:
> On Mon, Apr 16, 2012 at 06:50:12PM -0500, Robert Lee wrote:
>> Add common cpuidle init functionality that can be used by various
>> imx platforms.
>>
>> Signed-off-by: Robert Lee <rob.lee@...aro.org>
>> ---
>> diff --git a/arch/arm/plat-mxc/Makefile b/arch/arm/plat-mxc/Makefile
>> index e81290c..7c9e05f 100644
>> --- a/arch/arm/plat-mxc/Makefile
>> +++ b/arch/arm/plat-mxc/Makefile
>> @@ -16,6 +16,8 @@ obj-$(CONFIG_MXC_ULPI) += ulpi.o
>>  obj-$(CONFIG_MXC_USE_EPIT) += epit.o
>>  obj-$(CONFIG_MXC_DEBUG_BOARD) += 3ds_debugboard.o
>>  obj-$(CONFIG_CPU_FREQ_IMX)    += cpufreq.o
>> +obj-$(CONFIG_CPU_IDLE)    += cpuidle.o
>> +
>>  ifdef CONFIG_SND_IMX_SOC
>>  obj-y += ssi-fiq.o
>>  obj-y += ssi-fiq-ksym.o
>> diff --git a/arch/arm/plat-mxc/cpuidle.c b/arch/arm/plat-mxc/cpuidle.c
>> new file mode 100644
>> index 0000000..d1c9301
>> --- /dev/null
>> +++ b/arch/arm/plat-mxc/cpuidle.c
>> @@ -0,0 +1,89 @@
>> +/*
>> + * Copyright 2012 Freescale Semiconductor, Inc.
>> + * Copyright 2012 Linaro Ltd.
>> + *
>> + * The code contained herein is licensed under the GNU General Public
>> + * License. You may obtain a copy of the GNU General Public License
>> + * Version 2 or later at the following locations:
>> + *
>> + * http://www.opensource.org/licenses/gpl-license.html
>> + * http://www.gnu.org/copyleft/gpl.html
>> + */
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/io.h>
>> +#include <linux/cpuidle.h>
>> +#include <linux/hrtimer.h>
>> +#include <linux/err.h>
>> +#include <linux/slab.h>
>> +
>> +static struct cpuidle_device __percpu * imx_cpuidle_devices;
>> +static struct cpuidle_driver *drv;
>> +
>> +void __init imx_cpuidle_set_driver(struct cpuidle_driver *p)
>> +{
>> +     drv = p;
>> +}
>
> You like it complicated, eh? Why do you introduce a function which sets
> a variable...
>

This complication is used to deal with the timing of various levels of
init calls.  More explanation below.

>> +
>> +void imx_cpuidle_devices_uninit(void)
>> +{
>> +     int cpu_id;
>> +     struct cpuidle_device *dev;
>> +
>> +     for_each_possible_cpu(cpu_id) {
>> +             dev = per_cpu_ptr(imx_cpuidle_devices, cpu_id);
>> +             cpuidle_unregister_device(dev);
>> +     }
>> +
>> +     free_percpu(imx_cpuidle_devices);
>> +}
>> +
>> +static int __init imx_cpuidle_init(void)
>
> ... instead of passing it directly to the function which uses it?
>

If I called imx_cpuidle_init directly from imx5 or imx6q init
routines, it would be getting called before the coreinit_call of core
cpuidle causing a failure.  There were various other directions to
take and all seemed less desirable than this one.

One alternative would be to add a function to return the pointer to
the cpuidle driver object based on the machine type.  Functionality
exists to identify imx5 as a machine type but not imx6q, so I couldn't
use that machine based method without adding that extra code.

Another alternative would be to add a general platform lateinit_call
function to each platforms that support cpuidle.

>> +{
>> +     struct cpuidle_device *dev;
>> +     int cpu_id, ret;
>> +
>> +     if (!drv || drv->state_count > CPUIDLE_STATE_MAX) {
>> +             pr_err("%s: Invalid Input\n", __func__);
>
> You introduce a pointless error message on SoCs not setting a cpuidle
> driver. When will people learn that initcalls do not only run on
> machines they have on their desk?
>

Will fix in next version.

>> +             return -EINVAL;
>> +     }
>> +
>> +     ret = cpuidle_register_driver(drv);
>> +
>> +     if (ret) {
>> +             pr_err("%s: Failed to register cpuidle driver\n", __func__);
>
> It's always nice to add the return value to the error message to get a
> clue *what* went wrong. The function name though is rather
> uninteresting.

Will add the return value in the next version.

>
> Sascha
>
>
> --
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