Re: [PATCH v8 1/3] cpufreq: mediatek-hw: Add support for CPUFREQ HW

From: Lukasz Luba <lukasz.luba@arm.com>
To: Hector Yuan <hector.yuan@mediatek.com>
Cc: linux-mediatek@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org,
	Rob Herring <robh+dt@kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Maxime Ripard <mripard@kernel.org>,
	Santosh Shilimkar <ssantosh@kernel.org>,
	Amit Kucheria <amit.kucheria@linaro.org>,
	Stephen Boyd <sboyd@kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Dave Gerlach <d-gerlach@ti.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	wsd_upstream@mediatek.com
Subject: Re: [PATCH v8 1/3] cpufreq: mediatek-hw: Add support for CPUFREQ HW
Date: Thu, 19 Nov 2020 15:14:03 +0000	[thread overview]
Message-ID: <677bc381-6cab-85ec-8b9f-4c33dfb487fd@arm.com> (raw)
In-Reply-To: <1605793218.20463.5.camel@mtkswgap22>

On 11/19/20 1:40 PM, Hector Yuan wrote:
> On Thu, 2020-11-19 at 12:41 +0000, Lukasz Luba wrote:
>> Hi Hector,
>>
>> On 10/26/20 8:19 AM, Hector Yuan wrote:
>>> From: "Hector.Yuan" <hector.yuan@mediatek.com>
>>>
>>> Add cpufreq HW support.
>>>
>>> Signed-off-by: Hector.Yuan <hector.yuan@mediatek.com>
>>
>> [snip]
>>
>>> +
>>> +static int mtk_cpufreq_hw_cpu_init(struct cpufreq_policy *policy)
>>> +{
>>> +	struct cpufreq_mtk *c;
>>> +	struct device *cpu_dev;
>>> +	struct em_data_callback em_cb = EM_DATA_CB(mtk_cpufreq_get_cpu_power);
>>> +	struct pm_qos_request *qos_request;
>>> +	int sig, pwr_hw = CPUFREQ_HW_STATUS | SVS_HW_STATUS;
>>> +
>>> +	qos_request = kzalloc(sizeof(*qos_request), GFP_KERNEL);
>>> +	if (!qos_request)
>>> +		return -ENOMEM;
>>> +
>>> +	cpu_dev = get_cpu_device(policy->cpu);
>>> +	if (!cpu_dev) {
>>> +		pr_err("failed to get cpu%d device\n", policy->cpu);
>>> +		return -ENODEV;
>>> +	}
>>> +
>>> +	c = mtk_freq_domain_map[policy->cpu];
>>> +	if (!c) {
>>> +		pr_err("No scaling support for CPU%d\n", policy->cpu);
>>> +		return -ENODEV;
>>> +	}
>>> +
>>> +	cpumask_copy(policy->cpus, &c->related_cpus);
>>> +
>>> +	policy->freq_table = c->table;
>>> +	policy->driver_data = c;
>>
>> To control frequency transition rate in schedutil, you might
>> be interested in setting:
>>
>> policy->cpuinfo.transition_latency = <mtk_value_here>;
>>
>> Example, when this latency value comes from FW [1]
>>
> OK, I will add it in v9.
>>> +
>>> +	/* Let CPUs leave idle-off state for SVS CPU initializing */
>>> +	cpu_latency_qos_add_request(qos_request, 0);
>>> +
>>> +	/* HW should be in enabled state to proceed now */
>>> +	writel_relaxed(0x1, c->reg_bases[REG_FREQ_ENABLE]);
>>> +
>>> +	if (readl_poll_timeout(c->reg_bases[REG_FREQ_HW_STATE], sig,
>>> +			       (sig & pwr_hw) == pwr_hw, POLL_USEC,
>>> +			       TIMEOUT_USEC)) {
>>> +		if (!(sig & CPUFREQ_HW_STATUS)) {
>>> +			pr_info("cpufreq hardware of CPU%d is not enabled\n",
>>> +				policy->cpu);
>>> +			return -ENODEV;
>>> +		}
>>> +
>>> +		pr_info("SVS of CPU%d is not enabled\n", policy->cpu);
>>> +	}
>>> +
>>> +	em_dev_register_perf_domain(cpu_dev, c->nr_opp, &em_cb, policy->cpus);
>>
>> Please keep in mind that this is going to be changed soon with a new
>> argument: 'milliwatts'. It's queued in pm/linux-next [2].
>>
> OK, thanks for the remind.
>> Regards,
>> Lukasz
>>
>> [1]
>> https://elixir.bootlin.com/linux/latest/source/drivers/cpufreq/scmi-cpufreq.c#L194
>> [2]
>> https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=c250d50fe2ce627ca9805d9c8ac11cbbf922a4a6
>>
> 

Also, based on function mtk_cpufreq_hw_target_index(), which looks
really simple, you might consider to have fast_switch enabled.

It will allow SchedUtil governor to change frequency directly
and not create a dedicated deadline thread for it. It pays off.

You have to experiment with something like:

policy->fast_switch_possible  = true;

static struct cpufreq_driver cpufreq_mtk_hw_driver = {
...
	.fast_switch = mtk_cpufreq_hw_fast_switch
...
}

Again, scmi-cpufreq.c would be a good pattern to follow.