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Subject: Re: [RFC PATCH 09/11] devfreq: exynos-bus: Add interconnect
 functionality to exynos-bus
To:     =?UTF-8?B?QXJ0dXIgxZp3aWdvxYQ=?= <a.swigon@partner.samsung.com>,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
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        linux-pm@vger.kernel.org, dri-devel@lists.freedesktop.org
Cc:     krzk@kernel.org, myungjoo.ham@samsung.com, inki.dae@samsung.com,
        sw0312.kim@samsung.com, georgi.djakov@linaro.org,
        m.szyprowski@samsung.com
From:   Chanwoo Choi <cw00.choi@samsung.com>
Organization: Samsung Electronics
Message-ID: <96023e3b-1625-d534-d00e-e5b31a5db41d@samsung.com>
Date:   Fri, 9 Aug 2019 11:17:23 +0900
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Hi,

We need to discuss how to change or do refactoring on v2.
Actually, I don't know the your opinion and how to do it on v2.
You have to reply the answer and then after finished the discussion,
I recommend that you would rework and resend the v2 patches.

On 19. 8. 8. 오후 10:18, Artur Świgoń wrote:
> Hi,
> 
> Thank you for your remarks. I will take them into account while preparing RFCv2.
> 
> On Mon, 2019-07-29 at 10:52 +0900, Chanwoo Choi wrote:
>> Hi,
>>
>> On 19. 7. 23. 오후 9:20, Artur Świgoń wrote:
>>> This patch adds interconnect functionality to the exynos-bus devfreq
>>> driver.
>>>
>>> The SoC topology is a graph (or, more specifically, a tree) and most of its
>>> edges are taken from the devfreq parent-child hierarchy (cf.
>>> Documentation/devicetree/bindings/devfreq/exynos-bus.txt). The previous
>>> patch adds missing edges to the DT (under the name 'parent'). Due to
>>> unspecified relative probing order, -EPROBE_DEFER may be propagated to
>>> guarantee that a child is probed before its parent.
>>>
>>> Each bus is now an interconnect provider and an interconnect node as well
>>> (cf. Documentation/interconnect/interconnect.rst), i.e. every bus registers
>>> itself as a node. Node IDs are not hardcoded but rather assigned at
>>> runtime, in probing order (subject to the above-mentioned exception
>>> regarding relative order). This approach allows for using this driver with
>>> various Exynos SoCs.
>>>
>>> The devfreq target() callback provided by exynos-bus now selects either the
>>> frequency calculated by the devfreq governor or the frequency requested via
>>> the interconnect API for the given node, whichever is higher.
>>
>> Basically, I agree to support the QoS requirement between devices.
>> But, I think that need to consider the multiple cases.
>>
>>
>> 1. When changing the devfreq governor by user,
>> For example of the connection between bus_dmc/leftbus/display on patch8,
>> there are possible multiple cases with various devfreq governor
>> which is changed on the runtime by user through sysfs interface.
>>
>> If users changes the devfreq governor as following:
>> Before,
>> - bus_dmc (simple_ondemand, available frequency 100/200/300/400 MHz)
>> --> bus_leftbus(simple_ondemand, available frequency 100/200/300/400 MHz)
>> ----> bus_display(passive)
>>
>> After changed governor of bus_dmc,
>> if the min_freq by interconnect requirement is 400Mhz,
>> - bus_dmc (powersave) : min_freq and max_freq and cur_freq is 100MHz
>> --> bus_leftbus(simple_ondemand) : cur_freq is 400Mhz
>> ----> bus_display(passive)
>>
>> The final frequency is 400MHz of bus_dmc
>> even if the min_freq/max_freq/cur_freq is 100MHz.
>> It cannot show the correct min_freq/max_freq through
>> devfreq sysfs interface.
>>
>>
>> 2. When disabling the some frequency by devfreq-thermal throttling,
>> This patch checks the min_freq of interconnect requirement
>> in the exynos_bus_target() and exynos_bus_passive_target().
>> Also, it cannot show the correct min_freq/max_freq through
>> devfreq sysfs interface.
>>
>> For example of bus_dmc bus,
>> - The available frequencies are 100MHz, 200MHz, 300MHz, 400MHz
>> - Disable 400MHz by devfreq-thermal throttling 
>> - min_freq is 100MHz
>> - max_freq is 300MHz
>> - min_freq of interconnect is 400MHz
>>
>> In result, the final frequency is 400MHz by exynos_bus_target()
>> There are no problem for working. But, the user cannot know
>> reason why cur_freq is 400MHz even if max_freq is 300MHz.
>>
>> Basically, update_devfreq() considers the all constraints
>> of min_freq/max_freq to decide the proper target frequency.
>>
>>
>> 3.
>> I think that the exynos_bus_passive_target() is used for devfreq device
>> using 'passive' governor. The frequency already depends on the parent device.
>>
>> If already the parent devfreq device like bus_leftbus consider
>> the minimum frequency of QoS requirement like interconnect,
>> it is not necessary. The next frequency of devfreq device
>> with 'passive' governor, it will apply the QoS requirement
>> without any additional code.
>>
>>>
>>> Please note that it is not an error when CONFIG_INTERCONNECT is 'n', in
>>> which case all interconnect API functions are no-op.
>>>
>>> Signed-off-by: Artur Świgoń <a.swigon@partner.samsung.com>
>>> ---
>>>  drivers/devfreq/exynos-bus.c | 145 +++++++++++++++++++++++++++++++++++
>>>  1 file changed, 145 insertions(+)
>>>
>>> diff --git a/drivers/devfreq/exynos-bus.c b/drivers/devfreq/exynos-bus.c
>>> index 412511ca7703..12fb7c84ae50 100644
>>> --- a/drivers/devfreq/exynos-bus.c
>>> +++ b/drivers/devfreq/exynos-bus.c
>>> @@ -14,6 +14,7 @@
>>>  #include <linux/devfreq-event.h>
>>>  #include <linux/device.h>
>>>  #include <linux/export.h>
>>> +#include <linux/interconnect-provider.h>
>>>  #include <linux/module.h>
>>>  #include <linux/of.h>
>>>  #include <linux/pm_opp.h>
>>> @@ -23,6 +24,8 @@
>>>  #define DEFAULT_SATURATION_RATIO	40
>>>  #define DEFAULT_VOLTAGE_TOLERANCE	2
>>>  
>>> +#define icc_units_to_hz(x) ((x) * 1000UL / 8)
>>> +
>>>  struct exynos_bus {
>>>  	struct device *dev;
>>>  
>>> @@ -31,12 +34,17 @@ struct exynos_bus {
>>>  	unsigned int edev_count;
>>>  	struct mutex lock;
>>>  
>>> +	unsigned long min_freq;
>>>  	unsigned long curr_freq;
>>>  
>>>  	struct regulator *regulator;
>>>  	struct clk *clk;
>>>  	unsigned int voltage_tolerance;
>>>  	unsigned int ratio;
>>> +
>>> +	/* One provider per bus, one node per provider */
>>> +	struct icc_provider provider;
>>> +	struct icc_node *node;
>>>  };
>>>  
>>>  /*
>>> @@ -61,6 +69,13 @@ exynos_bus_ops_edev(enable_edev);
>>>  exynos_bus_ops_edev(disable_edev);
>>>  exynos_bus_ops_edev(set_event);
>>>  
>>> +static int exynos_bus_next_id(void)
>>> +{
>>> +	static int exynos_bus_node_id;
>>> +
>>> +	return exynos_bus_node_id++;
>>> +}
>>> +
>>>  static int exynos_bus_get_event(struct exynos_bus *bus,
>>>  				struct devfreq_event_data *edata)
>>>  {
>>> @@ -98,6 +113,8 @@ static int exynos_bus_target(struct device *dev, unsigned
>>> long *freq, u32 flags)
>>>  	unsigned long old_freq, new_freq, new_volt, tol;
>>>  	int ret = 0;
>>>  
>>> +	*freq = max(*freq, bus->min_freq);
>>> +
>>>  	/* Get new opp-bus instance according to new bus clock */
>>>  	new_opp = devfreq_recommended_opp(dev, freq, flags);
>>>  	if (IS_ERR(new_opp)) {
>>> @@ -208,6 +225,8 @@ static int exynos_bus_passive_target(struct device *dev,
>>> unsigned long *freq,
>>>  	unsigned long old_freq, new_freq;
>>>  	int ret = 0;
>>>  
>>> +	*freq = max(*freq, bus->min_freq);
>>> +
>>>  	/* Get new opp-bus instance according to new bus clock */
>>>  	new_opp = devfreq_recommended_opp(dev, freq, flags);
>>>  	if (IS_ERR(new_opp)) {
>>> @@ -251,6 +270,35 @@ static void exynos_bus_passive_exit(struct device *dev)
>>>  	clk_disable_unprepare(bus->clk);
>>>  }
>>>  
>>> +static int exynos_bus_icc_set(struct icc_node *src, struct icc_node *dst)
>>> +{
>>> +	struct exynos_bus *src_bus = src->data, *dst_bus = dst->data;
>>> +
>>> +	src_bus->min_freq = icc_units_to_hz(src->peak_bw);
>>> +	dst_bus->min_freq = icc_units_to_hz(dst->peak_bw);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static int exynos_bus_icc_aggregate(struct icc_node *node, u32 avg_bw,
>>> +				    u32 peak_bw, u32 *agg_avg, u32 *agg_peak)
>>> +{
>>> +	*agg_peak = *agg_avg = peak_bw;
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static struct icc_node *exynos_bus_icc_xlate(struct of_phandle_args *spec,
>>> +					     void *data)
>>> +{
>>> +	struct exynos_bus *bus = data;
>>> +
>>> +	if (spec->np != bus->dev->of_node)
>>> +		return ERR_PTR(-EINVAL);
>>> +
>>> +	return bus->node;
>>> +}
>>> +
>>>  static int exynos_bus_parent_parse_of(struct device_node *np,
>>>  					struct exynos_bus *bus)
>>>  {
>>> @@ -469,6 +517,95 @@ static int exynos_bus_profile_init_passive(struct
>>> exynos_bus *bus,
>>>  	return ret;
>>>  }
>>>  
>>> +static int exynos_bus_icc_connect(struct exynos_bus *bus)
>>> +{
>>> +	struct device_node *np = bus->dev->of_node;
>>> +	struct devfreq *parent_devfreq;
>>> +	struct icc_node *parent_node = NULL;
>>> +	struct of_phandle_args args;
>>> +	int ret = 0;
>>> +
>>> +	parent_devfreq = devfreq_get_devfreq_by_phandle(bus->dev, 0);
>>> +	if (!IS_ERR(parent_devfreq)) {
>>> +		struct exynos_bus *parent_bus;
>>> +
>>> +		parent_bus = dev_get_drvdata(parent_devfreq->dev.parent);
>>> +		parent_node = parent_bus->node;
>>> +	} else {
>>> +		/* Look for parent in DT */
>>> +		int num = of_count_phandle_with_args(np, "parent",
>>> +						     "#interconnect-cells");
>>> +		if (num != 1)
>>> +			goto out;
>>> +
>>> +		ret = of_parse_phandle_with_args(np, "parent",
>>> +						 "#interconnect-cells",
>>> +						 0, &args);
>>> +		if (ret < 0)
>>> +			goto out;
>>> +
>>> +		of_node_put(args.np);
>>> +
>>> +		parent_node = of_icc_get_from_provider(&args);
>>> +		if (IS_ERR(parent_node)) {
>>> +			/* May be -EPROBE_DEFER */
>>> +			ret = PTR_ERR(parent_node);
>>> +			goto out;
>>> +		}
>>> +	}
>>> +
>>> +	ret = icc_link_create(bus->node, parent_node->id);
>>> +
>>> +out:
>>> +	return ret;
>>> +}
>>> +
>>> +static int exynos_bus_icc_init(struct exynos_bus *bus)
>>> +{
>>> +	struct device *dev = bus->dev;
>>> +	struct icc_provider *provider = &bus->provider;
>>> +	struct icc_node *node;
>>> +	int id, ret;
>>> +
>>> +	/* Initialize the interconnect provider */
>>> +	provider->set = exynos_bus_icc_set;
>>> +	provider->aggregate = exynos_bus_icc_aggregate;
>>> +	provider->xlate = exynos_bus_icc_xlate;
>>> +	provider->dev = dev;
>>> +	provider->data = bus;
>>> +
>>> +	ret = icc_provider_add(provider);
>>> +	if (ret < 0)
>>> +		goto out;
>>> +
>>> +	id = exynos_bus_next_id();
>>> +	node = icc_node_create(id);
>>> +	if (IS_ERR(node)) {
>>> +		ret = PTR_ERR(node);
>>> +		goto err_node;
>>> +	}
>>> +
>>> +	bus->node = node;
>>> +	node->name = dev->of_node->name;
>>> +	node->data = bus;
>>> +	icc_node_add(node, provider);
>>> +
>>> +	ret = exynos_bus_icc_connect(bus);
>>> +	if (ret < 0)
>>> +		goto err_connect;
>>> +
>>> +out:
>>> +	return ret;
>>> +
>>> +err_connect:
>>> +	icc_node_del(node);
>>> +	icc_node_destroy(id);
>>> +err_node:
>>> +	icc_provider_del(provider);
>>> +
>>> +	return ret;
>>> +}
>>> +
>>>  static int exynos_bus_probe(struct platform_device *pdev)
>>>  {
>>>  	struct device *dev = &pdev->dev;
>>> @@ -517,6 +654,14 @@ static int exynos_bus_probe(struct platform_device
>>> *pdev)
>>>  			goto err;
>>>  	}
>>>  
>>> +	/*
>>> +	 * Initialize interconnect provider. A return value of -ENOTSUPP means
>>> +	 * that CONFIG_INTERCONNECT is disabled.
>>> +	 */
>>> +	ret = exynos_bus_icc_init(bus);
>>> +	if (ret < 0 && ret != -ENOTSUPP)
>>> +		goto err;
>>> +
>>>  	max_state = bus->devfreq->profile->max_state;
>>>  	min_freq = (bus->devfreq->profile->freq_table[0] / 1000);
>>>  	max_freq = (bus->devfreq->profile->freq_table[max_state - 1] / 1000);
>>>
>>
>>


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics