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Subject: Re: [PATCH v6 3/6] thermal: Add generic power domain warming device
 driver.
To:     Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thara Gopinath <thara.gopinath@linaro.org>
Cc:     rui.zhang@intel.com, ulf.hansson@linaro.org,
        bjorn.andersson@linaro.org, agross@kernel.org, robh@kernel.org,
        amit.kucheria@verdurent.com, mark.rutland@arm.com,
        rjw@rjwysocki.net, linux-pm@vger.kernel.org,
        devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20200604015317.31389-1-thara.gopinath@linaro.org>
 <20200604015317.31389-4-thara.gopinath@linaro.org>
 <733d118d-45a3-b981-4820-5d841e921a8d@linaro.org>
From:   Lukasz Luba <lukasz.luba@arm.com>
Message-ID: <79a35aea-51c1-ed76-5107-35d2191b028f@arm.com>
Date:   Tue, 7 Jul 2020 11:58:36 +0100
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Hi Daniel and Thara

On 7/3/20 11:02 AM, Daniel Lezcano wrote:
> 
> Hi Thara,
> 
> sorry for the delay.
> 
> Added Lukasz.

Thank you for adding me.
I will go through the patches to understand them and build
the context. I can see some interesting idea described below.

Regards,
Lukasz

> 
> On 04/06/2020 03:53, Thara Gopinath wrote:
>> Resources modeled as power domains in linux kernel can  be used to warm the
>> SoC(eg. mx power domain on sdm845).  To support this feature, introduce a
>> generic power domain warming device driver that can be plugged into the
>> thermal framework (The thermal framework itself requires further
>> modifiction to support a warming device in place of a cooling device.
>> Those extensions are not introduced in this patch series).
> 
> The patch itself looks fine but I'm not very convinced about using a
> specific driver as a warming device.
> 
> It is all about changing the performance state of a device and the power
> domain is a way to access the associated callback.
> 
> It could be used as a cooling device as well.
> 
> The cpufreq cooling device could be used as a warming device and the way
> we access the performance state is the freq qos.
> 
> We end up with different ways to do the same thing : change the
> performance state.
> 
> On the other side, the energy model is being moved to the struct device,
> so we will have gpu and cpu using it to retrieve a performance state
> given a power value.
> 
> My opinion is instead of multiplying the ways to do the same think, we
> should find a way to unify all the passive cooling devices into a single
> generic performance state based mitigation device.
> 
> It does not imply to make all the passive cooling device changes but
> provide a generic one first.
> 
> The ideal would be to register a struct device as a performance state
> capable device and use the energy model stored in it.
> 
> In the meantime, the energy model should embed a couple of callbacks
> get_power / set_power to set the performance state.
> 
> That implies a bit of more work, but IMHO it is worth to do.
> 
> Does it make sense ?
> 
> 
>> ---
>>
>> v3->v4:
>> 	- Removed late_init hook pd_warming_device_ops.
>> 	- Use of_genpd_add_device instead of pm_genpd_add_device to attach
>> 	  device to the generic power domain.
>> 	- Use thermal_of_cooling_device_parent_register to register the
>> 	  cooling device so that the device with genpd attached can be
>> 	  made parent of the cooling device.
>> 	- With above changes, remove reference to generic_pm_domain in
>> 	  pd_warming_device.
>>
>> v4->v5:
>> 	- All the below changes are as per Ulf's review comments.
>> 	- Renamed pwr_domain_warming.c and pwr_domain_warming.h to
>> 	  pd_warming.c and pd_warming.h.
>> 	- Renamed pwr_domain_warming_register API to
>> 	  of_pd_warming_register.
>> 	- Dropped in-param pd_name to of_pd_warming_register.
>> 	- Introduced ID allocator to uniquely identify each power domain
>> 	  warming device.
>> 	- Introduced pd_warming_release to handle device kfree for
>> 	  pd_warming_device.
>> 	- Introduced pm_genpd_remove_device in the error exit path
>> 	  of of_pd_warming_register.
>> v5->v6:
>> 	- Fixed issues with ->release() and kfree(dev) as pointed
>> 	  out by Ulf.
>>
>>   drivers/thermal/Kconfig      |  10 +++
>>   drivers/thermal/Makefile     |   4 +
>>   drivers/thermal/pd_warming.c | 169 +++++++++++++++++++++++++++++++++++
>>   include/linux/pd_warming.h   |  29 ++++++
>>   4 files changed, 212 insertions(+)
>>   create mode 100644 drivers/thermal/pd_warming.c
>>   create mode 100644 include/linux/pd_warming.h
>>
>> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
>> index e53314ea9e25..3a0bcf3e8bd9 100644
>> --- a/drivers/thermal/Kconfig
>> +++ b/drivers/thermal/Kconfig
>> @@ -206,6 +206,16 @@ config DEVFREQ_THERMAL
>>   
>>   	  If you want this support, you should say Y here.
>>   
>> +config PWR_DOMAIN_WARMING_THERMAL
>> +	bool "Power Domain based warming device"
>> +	depends on PM_GENERIC_DOMAINS_OF
>> +	help
>> +	  This implements the generic power domain based warming
>> +	  mechanism through increasing the performance state of
>> +	  a power domain.
>> +
>> +	  If you want this support, you should say Y here.
>> +
>>   config THERMAL_EMULATION
>>   	bool "Thermal emulation mode support"
>>   	help
>> diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
>> index 86c506410cc0..14fa696a08bd 100644
>> --- a/drivers/thermal/Makefile
>> +++ b/drivers/thermal/Makefile
>> @@ -28,7 +28,11 @@ thermal_sys-$(CONFIG_CLOCK_THERMAL)	+= clock_cooling.o
>>   # devfreq cooling
>>   thermal_sys-$(CONFIG_DEVFREQ_THERMAL) += devfreq_cooling.o
>>   
>> +#pwr domain warming
>> +thermal_sys-$(CONFIG_PWR_DOMAIN_WARMING_THERMAL)	+= pd_warming.o
>> +
>>   obj-$(CONFIG_K3_THERMAL)	+= k3_bandgap.o
>> +
>>   # platform thermal drivers
>>   obj-y				+= broadcom/
>>   obj-$(CONFIG_THERMAL_MMIO)		+= thermal_mmio.o
>> diff --git a/drivers/thermal/pd_warming.c b/drivers/thermal/pd_warming.c
>> new file mode 100644
>> index 000000000000..1ea93481c79b
>> --- /dev/null
>> +++ b/drivers/thermal/pd_warming.c
>> @@ -0,0 +1,169 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (c) 2019, Linaro Ltd
>> + */
>> +#include <linux/err.h>
>> +#include <linux/kernel.h>
>> +#include <linux/init.h>
>> +#include <linux/of_device.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/module.h>
>> +#include <linux/pm_runtime.h>
>> +#include <linux/slab.h>
>> +#include <linux/pd_warming.h>
>> +
>> +struct pd_warming_device {
>> +	struct thermal_cooling_device *cdev;
>> +	struct device dev;
>> +	int id;
>> +	int max_state;
>> +	int cur_state;
>> +	bool runtime_resumed;
>> +};
>> +
>> +static DEFINE_IDA(pd_ida);
>> +
>> +static int pd_wdev_get_max_state(struct thermal_cooling_device *cdev,
>> +				 unsigned long *state)
>> +{
>> +	struct pd_warming_device *pd_wdev = cdev->devdata;
>> +
>> +	*state = pd_wdev->max_state;
>> +	return 0;
>> +}
>> +
>> +static int pd_wdev_get_cur_state(struct thermal_cooling_device *cdev,
>> +				 unsigned long *state)
>> +{
>> +	struct pd_warming_device *pd_wdev = cdev->devdata;
>> +
>> +	*state = dev_pm_genpd_get_performance_state(&pd_wdev->dev);
>> +
>> +	return 0;
>> +}
>> +
>> +static int pd_wdev_set_cur_state(struct thermal_cooling_device *cdev,
>> +				 unsigned long state)
>> +{
>> +	struct pd_warming_device *pd_wdev = cdev->devdata;
>> +	struct device *dev = &pd_wdev->dev;
>> +	int ret;
>> +
>> +	ret = dev_pm_genpd_set_performance_state(dev, state);
>> +
>> +	if (ret)
>> +		return ret;
>> +
>> +	if (state && !pd_wdev->runtime_resumed) {
>> +		ret = pm_runtime_get_sync(dev);
>> +		pd_wdev->runtime_resumed = true;
>> +	} else if (!state && pd_wdev->runtime_resumed) {
>> +		ret = pm_runtime_put(dev);
>> +		pd_wdev->runtime_resumed = false;
>> +	}
>> +
>> +	return ret;
>> +}
>> +
>> +static struct thermal_cooling_device_ops pd_warming_device_ops = {
>> +	.get_max_state	= pd_wdev_get_max_state,
>> +	.get_cur_state	= pd_wdev_get_cur_state,
>> +	.set_cur_state	= pd_wdev_set_cur_state,
>> +};
>> +
>> +static void pd_warming_release(struct device *dev)
>> +{
>> +	struct pd_warming_device *pd_wdev;
>> +
>> +	pd_wdev = container_of(dev, struct pd_warming_device, dev);
>> +	kfree(pd_wdev);
>> +}
>> +
>> +struct thermal_cooling_device *
>> +of_pd_warming_register(struct device *parent, int pd_id)
>> +{
>> +	struct pd_warming_device *pd_wdev;
>> +	struct of_phandle_args pd_args;
>> +	char cdev_name[THERMAL_NAME_LENGTH];
>> +	int ret;
>> +
>> +	pd_wdev = kzalloc(sizeof(*pd_wdev), GFP_KERNEL);
>> +	if (!pd_wdev)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	dev_set_name(&pd_wdev->dev, "%s_%d_warming_dev",
>> +		     dev_name(parent), pd_id);
>> +	pd_wdev->dev.parent = parent;
>> +	pd_wdev->dev.release = pd_warming_release;
>> +
>> +	ret = device_register(&pd_wdev->dev);
>> +	if (ret) {
>> +		put_device(&pd_wdev->dev);
>> +		goto out;
>> +	}
>> +
>> +	ret = ida_simple_get(&pd_ida, 0, 0, GFP_KERNEL);
>> +	if (ret < 0)
>> +		goto unregister_device;
>> +
>> +	pd_wdev->id = ret;
>> +
>> +	pd_args.np = parent->of_node;
>> +	pd_args.args[0] = pd_id;
>> +	pd_args.args_count = 1;
>> +
>> +	ret = of_genpd_add_device(&pd_args, &pd_wdev->dev);
>> +
>> +	if (ret)
>> +		goto remove_ida;
>> +
>> +	ret = dev_pm_genpd_performance_state_count(&pd_wdev->dev);
>> +	if (ret < 0)
>> +		goto out_genpd;
>> +
>> +	pd_wdev->max_state = ret - 1;
>> +	pm_runtime_enable(&pd_wdev->dev);
>> +	pd_wdev->runtime_resumed = false;
>> +
>> +	snprintf(cdev_name, sizeof(cdev_name), "thermal-pd-%d", pd_wdev->id);
>> +	pd_wdev->cdev = thermal_of_cooling_device_register
>> +					(NULL, cdev_name, pd_wdev,
>> +					 &pd_warming_device_ops);
>> +	if (IS_ERR(pd_wdev->cdev)) {
>> +		pr_err("unable to register %s cooling device\n", cdev_name);
>> +		ret = PTR_ERR(pd_wdev->cdev);
>> +		goto out_runtime_disable;
>> +	}
>> +
>> +	return pd_wdev->cdev;
>> +
>> +out_runtime_disable:
>> +	pm_runtime_disable(&pd_wdev->dev);
>> +out_genpd:
>> +	pm_genpd_remove_device(&pd_wdev->dev);
>> +remove_ida:
>> +	ida_simple_remove(&pd_ida, pd_wdev->id);
>> +unregister_device:
>> +	device_unregister(&pd_wdev->dev);
>> +out:
>> +	return ERR_PTR(ret);
>> +}
>> +EXPORT_SYMBOL_GPL(of_pd_warming_register);
>> +
>> +void pd_warming_unregister(struct thermal_cooling_device *cdev)
>> +{
>> +	struct pd_warming_device *pd_wdev = cdev->devdata;
>> +	struct device *dev = &pd_wdev->dev;
>> +
>> +	if (pd_wdev->runtime_resumed) {
>> +		dev_pm_genpd_set_performance_state(dev, 0);
>> +		pm_runtime_put(dev);
>> +		pd_wdev->runtime_resumed = false;
>> +	}
>> +	pm_runtime_disable(dev);
>> +	pm_genpd_remove_device(dev);
>> +	ida_simple_remove(&pd_ida, pd_wdev->id);
>> +	thermal_cooling_device_unregister(cdev);
>> +	device_unregister(dev);
>> +}
>> +EXPORT_SYMBOL_GPL(pd_warming_unregister);
>> diff --git a/include/linux/pd_warming.h b/include/linux/pd_warming.h
>> new file mode 100644
>> index 000000000000..550a5683b56d
>> --- /dev/null
>> +++ b/include/linux/pd_warming.h
>> @@ -0,0 +1,29 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (c) 2019, Linaro Ltd.
>> + */
>> +#ifndef __PWR_DOMAIN_WARMING_H__
>> +#define __PWR_DOMAIN_WARMING_H__
>> +
>> +#include <linux/pm_domain.h>
>> +#include <linux/thermal.h>
>> +
>> +#ifdef CONFIG_PWR_DOMAIN_WARMING_THERMAL
>> +struct thermal_cooling_device *
>> +of_pd_warming_register(struct device *parent, int pd_id);
>> +
>> +void pd_warming_unregister(struct thermal_cooling_device *cdev);
>> +
>> +#else
>> +static inline struct thermal_cooling_device *
>> +of_pd_warming_register(struct device *parent, int pd_id)
>> +{
>> +	return ERR_PTR(-ENOSYS);
>> +}
>> +
>> +static inline void
>> +pd_warming_unregister(struct thermal_cooling_device *cdev)
>> +{
>> +}
>> +#endif /* CONFIG_PWR_DOMAIN_WARMING_THERMAL */
>> +#endif /* __PWR_DOMAIN_WARMING_H__ */
>>
> 
>