Subject: [PATCH v14 03/10] qcom: spm: Add Subsystem Power Manager driver

From: [email-masked] (Daniel Lezcano)
Date: Tue, 16 Dec 2014 15:12:22 +0100

On 12/04/2014 07:20 PM, Arnd Bergmann wrote:
> On Thursday 04 December 2014 09:28:34 Lina Iyer wrote:
>> On Thu, Dec 04 2014 at 02:02 -0700, Arnd Bergmann wrote:
>>> On Thursday 04 December 2014 09:52:39 Daniel Lezcano wrote:
>>>> On 12/03/2014 09:35 PM, Arnd Bergmann wrote:
>>>>> On Wednesday 03 December 2014 07:31:22 Lina Iyer wrote:
>>>>>>>>> +static int __init qcom_spm_init(void)
>>>>>>>>> +{
>>>>>>>>> +    int ret;
>>>>>>>>> +
>>>>>>>>> +    /*
>>>>>>>>> +     * cpuidle driver need to registered before the cpuidle device
>>>>>>>>> +     * for any cpu. Register the device for the the cpuidle driver.
>>>>>>>>> +     */
>>>>>>>>> +    ret = platform_device_register(&qcom_cpuidle_drv);
>>>>>>>>> +    if (ret)
>>>>>>>>> +        return ret;
>>>>>>>> Stephen pointed out that we would have the platform device lying around
>>>>>>>> on a non-QCOM device when using multi_v7_defconfig.
>>>>>>>
>>>>>>> Perhaps I am missing the point, but this is not supposed to happen, no ?
>>>>>>>
>>>>>> This would happen, since the file would compile on multi_v7 and we would
>>>>>> initialize and register this device regardless. The cpuidle-qcom.c
>>>>>> driver probe would bail out looking for a matching compatible property.
>>>>>> So we would not register a cpuidle driver but the device would lay
>>>>>> around.
>>>>>
>>>>> I think the problem is registering a platform_device. I've complained
>>>>> about this before, but it still seems to get copied all over the
>>>>> place. Please don't do this but have a driver that looks at DT to
>>>>> figure out whether to access hardware or not.
>>>>
>>>> We did this approach but, I can remember why, someone was complaining
>>>> about it also
>>>>
>>>> The platform device/driver paradigm allowed us to split the arch
>>>> specific parts by passing the pm ops through the platform data.
>>>>
>>>> Would make sense to have a single common place for the ARM arch where we
>>>> initialize the platform device for cpuidle ?
>>>
>>> No. It's really not a device, and if you pretend that it is, you get
>>> into problems like this.
>>
>> Arnd, the problem is that the provides function pointers to the SoC code
>> that the cpuilde driver uses to call based on the idle state.
>>
>> After much discussions, we came down to using function pointers from
>> translating from DT strings, other than using that again, I dont see a
>> good way of achieving the ability of cpuidle driver staying a separate
>> driver from the SPM driver.
>>
>> Daniel, thoughts?
>
> Maybe the problem is trying too hard to separate two things that really
> belong together then. In general, the strategy of coming up with subsystems
> for a class of devices and them turning platform code into drivers for
> that subsystem has worked out really well, but I think for cpufreq, cpuidle
> and smp, it really hasn't, and in the third case we haven't even tried
> coming up with a subsystem for that reason.
>
> Having all cpuidle code generally live in drivers/cpuidle is still a good
> idea IMO, but using a platform device just for the purpose of passing
> data between some platform specific code and another platform specific
> driver hasn't worked out that well here.

At the beginning, all that become from not including mach files from the 
drivers directory which make sense.

Perhaps it is time to write a similar mechanism for the cpuidle drivers 
where we can still separate the low level PM code from the generic 
cpuidle code.

Something like (very roughly):

Index: cpuidle-next/drivers/cpuidle/driver.c
===================================================================
--- cpuidle-next.orig/drivers/cpuidle/driver.c	2014-12-16 
14:04:51.750861310 +0100
+++ cpuidle-next/drivers/cpuidle/driver.c	2014-12-16 15:09:52.202706756 
+0100
@@ -178,6 +178,45 @@ static void __cpuidle_driver_init(struct
  	}
  }

+struct cpuidle_ops_reg {
+	const char *name;
+	struct cpuidle_ops *ops;
+	struct list_head *list;
+};
+
+static LIST_HEAD(ops_list);
+
+static struct cpuidle_ops *cpuidle_find_ops(const char *name)
+{
+	struct cpuidle_ops_reg *ops_reg;
+
+	list_for_each_entry(ops_reg, &ops_list, list) {
+		if (!strcmp(ops_reg->name, name))
+			return ops_reg->ops;
+	}
+
+	return NULL;
+}
+
+int cpuidle_register_ops(const char *name, struct cpuidle_ops *ops)
+{
+	struct cpuidle_ops_reg *reg;
+
+	reg = kmalloc(sizeof(*reg), GFP_KERNEL);
+	if (!reg)
+		return -ENOMEM;
+
+	reg->name = name;
+	reg->ops = ops;
+	INIT_LIST_HEAD(&reg->list);
+
+	spin_lock(&cpuidle_driver_lock);
+	list_add(&ops_list, &reg->list);
+	spin_unlock(&cpuidle_driver_lock);
+
+	return 0;
+}
+
  /**
   * __cpuidle_register_driver: register the driver
   * @drv: a valid pointer to a struct cpuidle_driver
@@ -194,6 +233,7 @@ static void __cpuidle_driver_init(struct
  static int __cpuidle_register_driver(struct cpuidle_driver *drv)
  {
  	int ret;
+	struct cpuidle_ops *ops;

  	if (!drv || !drv->state_count)
  		return -EINVAL;
@@ -201,6 +241,10 @@ static int __cpuidle_register_driver(str
  	if (cpuidle_disabled())
  		return -ENODEV;

+	ops = cpuidle_find_ops(drv->name);
+	if (ops)
+		drv->ops = ops;
+
  	__cpuidle_driver_init(drv);

  	ret = __cpuidle_set_driver(drv);
Index: cpuidle-next/include/linux/cpuidle.h
===================================================================
--- cpuidle-next.orig/include/linux/cpuidle.h	2014-12-16 
14:06:09.442858231 +0100
+++ cpuidle-next/include/linux/cpuidle.h	2014-12-16 14:59:46.594730753 +0100
@@ -109,11 +109,21 @@ static inline int cpuidle_get_last_resid
   * CPUIDLE DRIVER INTERFACE *
   ****************************/

+struct cpuidle_ops {
+	int (*standby)(struct cpuidle_driver *drv,
+		       struct cpuidle_device *dev);
+	int (*retention)(struct cpuidle_driver *drv,
+			 struct cpuidle_device *dev);
+	int (*poweroff)(struct cpuidle_driver *drv,
+			struct cpuidle_device *dev);
+};
+
  struct cpuidle_driver {
  	const char		*name;
  	struct module 		*owner;
  	int                     refcnt;

+	struct cpuidle_ops      *ops;
          /* used by the cpuidle framework to setup the broadcast timer */
  	unsigned int            bctimer:1;
  	/* states array must be ordered in decreasing power consumption */

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