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

Lukasz Luba
2020-11-19T15:14:23Z

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.