Re: [PATCH v2 3/4] cpufreq: mediatek: add Mediatek cpufreq driver

[Pi-Cheng Chen <pi-cheng.chen@linaro.org>]

Hi Viresh,

Thanks for reviewing.
Please see my reply below:

On 4 March 2015 at 19:09, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> Haven't reviewed it completely yet, but this is all I have done.
>
> On 4 March 2015 at 14:19, pi-cheng.chen <pi-cheng.chen@linaro.org> wrote:
>
>> +static int mtk_cpufreq_notify(struct notifier_block *nb,
>> +                             unsigned long action, void *data)
>> +{
>> +       struct cpufreq_freqs *freqs = data;
>> +       struct cpu_opp_table *opp_tbl = dvfs_info->opp_tbl;
>
> There is only one dvfs info ? but there are two clusters, sorry got confused
> a bit..

There are 2 clusters, but only the big cluster need to do voltage scaling in the
notifier, since the voltage controlling is done by cpufreq-dt driver
in this version.
Therefore only one dvfs_info struct here.

>
>> +       int old_vproc, new_vproc, old_index, new_index;
>> +
>> +       if (!cpumask_test_cpu(freqs->cpu, &dvfs_info->cpus))
>> +               return NOTIFY_DONE;
>> +
>> +       old_vproc = regulator_get_voltage(dvfs_info->proc_reg);
>> +       old_index = cpu_opp_table_get_volt_index(old_vproc);
>> +       new_index = cpu_opp_table_get_freq_index(freqs->new * 1000);
>> +       new_vproc = opp_tbl[new_index].vproc;
>> +
>> +       if (old_vproc == new_vproc)
>> +               return 0;
>> +
>> +       if ((action == CPUFREQ_PRECHANGE && old_vproc < new_vproc) ||
>> +           (action == CPUFREQ_POSTCHANGE && old_vproc > new_vproc))
>> +               mtk_cpufreq_voltage_trace(old_index, new_index);
>> +
>> +       return NOTIFY_OK;
>> +}
>> +
>> +static struct notifier_block mtk_cpufreq_nb = {
>> +       .notifier_call = mtk_cpufreq_notify,
>> +};
>> +
>> +static int cpu_opp_table_init(struct device *dev)
>> +{
>> +       struct device *cpu_dev = dvfs_info->cpu_dev;
>> +       struct cpu_opp_table *opp_tbl;
>> +       struct dev_pm_opp *opp;
>> +       int ret, cnt, i;
>> +       unsigned long rate, vproc, vsram;
>> +
>> +       ret = of_init_opp_table(cpu_dev);
>> +       if (ret) {
>> +               dev_err(dev, "Failed to init mtk_opp_table: %d\n", ret);
>> +               return ret;
>> +       }
>> +
>> +       rcu_read_lock();
>> +
>> +       cnt = dev_pm_opp_get_opp_count(cpu_dev);
>> +       if (cnt < 0) {
>> +               dev_err(cpu_dev, "No OPP table is found: %d", cnt);
>> +               ret = cnt;
>> +               goto out_free_opp_tbl;
>> +       }
>> +
>> +       opp_tbl = devm_kcalloc(dev, (cnt + 1), sizeof(struct cpu_opp_table),
>> +                              GFP_ATOMIC);
>> +       if (!opp_tbl) {
>> +               ret = -ENOMEM;
>> +               goto out_free_opp_tbl;
>> +       }
>> +
>> +       for (i = 0, rate = 0; i < cnt; i++, rate++) {
>> +               opp = dev_pm_opp_find_freq_ceil(cpu_dev, &rate);
>> +               if (IS_ERR(opp)) {
>> +                       ret = PTR_ERR(opp);
>> +                       goto out_free_opp_tbl;
>> +               }
>> +
>> +               vproc = dev_pm_opp_get_voltage(opp);
>> +               vproc = get_regulator_voltage_ceil(dvfs_info->proc_reg, vproc);
>> +               vsram = vproc + VOLT_SHIFT_LOWER_LIMIT;
>> +               vsram = get_regulator_voltage_ceil(dvfs_info->sram_reg, vsram);
>> +
>> +               if (vproc < 0 || vsram < 0) {
>> +                       ret = -EINVAL;
>> +                       goto out_free_opp_tbl;
>> +               }
>> +
>> +               opp_tbl[i].freq = rate;
>> +               opp_tbl[i].vproc = vproc;
>> +               opp_tbl[i].vsram = vsram;
>> +       }
>> +
>> +       opp_tbl[i].freq = 0;
>> +       opp_tbl[i].vproc = -1;
>> +       opp_tbl[i].vsram = -1;
>> +       dvfs_info->opp_tbl = opp_tbl;
>> +
>> +out_free_opp_tbl:
>> +       rcu_read_unlock();
>> +       of_free_opp_table(cpu_dev);
>> +
>> +       return ret;
>> +}
>> +
>> +static struct cpufreq_cpu_domain *get_cpu_domain(struct list_head *domain_list,
>> +                                                int cpu)
>> +{
>> +       struct list_head *node;
>> +
>> +       list_for_each(node, domain_list) {
>> +               struct cpufreq_cpu_domain *domain;
>> +
>> +               domain = container_of(node, struct cpufreq_cpu_domain, node);
>> +               if (cpumask_test_cpu(cpu, &domain->cpus))
>> +                       return domain;
>> +       }
>> +
>> +       return NULL;
>> +}
>> +
>> +static int mtk_cpufreq_probe(struct platform_device *pdev)
>
> On a dual cluster big LITTLE (your system), how many times is probe
> getting called ? Once or twice, i.e. for each cluster ??

The probe function will be called only once since it's triggered by the device
tree node in the 2nd patch of this series. Though it's not acceptable obviously.

>
>> +{
>> +       struct clk *inter_clk;
>> +       struct cpufreq_dt_platform_data *pd;
>> +       struct platform_device *dev;
>> +       unsigned long inter_freq;
>> +       int cpu, ret;
>> +
>> +       inter_clk = clk_get(&pdev->dev, NULL);
>
> How is this supposed to work ? How will pdev->dev give intermediate
> clock ?

It works with the the device tree binding in the 2nd patch of this series, too.
Since the cpufreq node is not allowed, would you have some suggestions on
how to get the intermediate clock source in this case?

>
>> +       if (IS_ERR(inter_clk)) {
>> +               if (PTR_ERR(inter_clk) == -EPROBE_DEFER) {
>> +                       dev_warn(&pdev->dev, "clock not ready. defer probeing.\n");
>> +                       return -EPROBE_DEFER;
>> +               }
>> +
>> +               dev_err(&pdev->dev, "Failed to get intermediate clock\n");
>> +               return -ENODEV;
>> +       }
>> +       inter_freq = clk_get_rate(inter_clk);
>> +
>> +       pd = devm_kzalloc(&pdev->dev, sizeof(*pd), GFP_KERNEL);
>> +       if (!pd)
>> +               return -ENOMEM;
>> +
>> +       dvfs_info = devm_kzalloc(&pdev->dev, sizeof(*dvfs_info), GFP_KERNEL);
>> +       if (!dvfs_info)
>> +               return -ENOMEM;
>
> Instead of two allocations, you could have made pd part of dvfs_info
> and allocated only
> once.

Will do it.

>
>> +
>> +       pd->independent_clocks = 1,
>
> s/,/; ??

It's strange that I didn't get a compiling error here.
Will fix it.

>
>> +       INIT_LIST_HEAD(&pd->domain_list);
>> +
>> +       for_each_possible_cpu(cpu) {
>> +               struct device *cpu_dev;
>> +               struct cpufreq_cpu_domain *new_domain;
>> +               struct regulator *proc_reg, *sram_reg;
>> +
>> +               cpu_dev = get_cpu_device(cpu);
>
> This should be done in the below if block only.

Will do it.

>
>> +               if (!dvfs_info->cpu_dev) {
>> +                       proc_reg = regulator_get_exclusive(cpu_dev, "proc");
>> +                       sram_reg = regulator_get_exclusive(cpu_dev, "sram");
>> +
>> +                       if (PTR_ERR(proc_reg) == -EPROBE_DEFER ||
>> +                           PTR_ERR(sram_reg) == -EPROBE_DEFER)
>> +                               return -EPROBE_DEFER;
>> +
>> +                       if (!IS_ERR_OR_NULL(proc_reg) &&
>> +                           !IS_ERR_OR_NULL(sram_reg)) {
>> +                               dvfs_info->cpu_dev = cpu_dev;
>> +                               dvfs_info->proc_reg = proc_reg;
>> +                               dvfs_info->sram_reg = sram_reg;
>> +                               cpumask_copy(&dvfs_info->cpus,
>> +                                            &cpu_topology[cpu].core_sibling);
>> +                       }
>> +               }
>> +
>> +               if (get_cpu_domain(&pd->domain_list, cpu))
>> +                       continue;
>
> This isn't required if you do below..

Please see below.

>
>> +
>> +               new_domain = devm_kzalloc(&pdev->dev, sizeof(*new_domain),
>> +                                         GFP_KERNEL);
>> +               if (!new_domain)
>> +                       return -ENOMEM;
>> +
>> +               cpumask_copy(&new_domain->cpus,
>> +                            &cpu_topology[cpu].core_sibling);
>> +               new_domain->intermediate_freq = inter_freq;
>> +               list_add(&new_domain->node, &pd->domain_list);
>
> Just issue a 'break' from here as you don't want to let this loop run again.

Please see below.

>
>> +       }
>> +
>> +       if (IS_ERR_OR_NULL(dvfs_info->proc_reg) ||
>> +           IS_ERR_OR_NULL(dvfs_info->sram_reg)) {
>> +               dev_err(&pdev->dev, "Failed to get regulators\n");
>> +               return -ENODEV;
>> +       }
>
> If you really need these, then don't allocate new_domain unless you find a CPU
> with these regulators..

Please see below.

>
>> +       ret = cpu_opp_table_init(&pdev->dev);
>> +       if (ret) {
>> +               dev_err(&pdev->dev, "Failed to setup cpu_opp_table: %d\n",
>> +                       ret);
>> +               return ret;
>> +       }
>> +
>> +       ret = cpufreq_register_notifier(&mtk_cpufreq_nb,
>> +                                       CPUFREQ_TRANSITION_NOTIFIER);
>> +       if (ret) {
>> +               dev_err(&pdev->dev, "Failed to register cpufreq notifier\n");
>> +               return ret;
>> +       }
>
> Don't want to free OPP table here on error ?

Please correct me if I was wrong. Since the OPP table in the dvfs_info is
allocated by devm_kzalloc(), it is supposed to be freed if the probe function
failed, isn't it?

And the OPP table initialized by of_init_opp_table() in cpu_opp_table_init()
was freed right before the function return since it will be initialized again in
the cpufreq-dt driver.

>
>> +       dev = platform_device_register_data(NULL, "cpufreq-dt", -1, pd,
>> +                                           sizeof(*pd));
>
> So this routine is going to be called only once. Then how are you
> initializing stuff
> for both the clusters in the upper for loop ? It looked very very confusing.

Please let me clarify this here.
We have two clusters, one for big and another for little cores. For
the little cores'
cluster, only one voltage source needs to be controlled when doing CPU DVFS.
Therefore the voltage scaling of little cores' cluster is done in the
cpufreq-dt.
But for the big cores' cluster, there are two voltage sources here to
be controlled
and these two voltage source need to be scaled up and down in a SoC specific
manner which is implemented in the mtk_cpufreq_voltage_trace() function.
Hence, we put the voltage scaling of big cores' cluster in the cpufreq
notifier and
that's also why we need a mtk-cpufreq driver in addition to cpufreq-dt.

In the confusing loop above, I am trying to solve two problems:
1. to find out which CPUs shares the same clock / power domains among all CPUs
2. to initialize the dvfs_info which is only needed by big cores' cluster

I think that's why the loop looks so confusing. Maybe doing it in two
separate loops
will make the code more readable? I'll try it in next version.

>
>> +       if (IS_ERR(dev)) {
>> +               dev_err(&pdev->dev,
>> +                       "Failed to register cpufreq-dt platform device\n");
>> +               return PTR_ERR(dev);
>> +       }
>> +
>> +       return 0;
>> +}
>> +
>> +static const struct of_device_id mtk_cpufreq_match[] = {
>> +       {
>> +               .compatible = "mediatek,mtk-cpufreq",
>
> Can't you use "mediatek,mt8173" here ?

Again, the device tree binding in the 2nd patch of this series. I am
trying to get
the intermediate clock source from the device tree. The reason why I am doing
this is the intermediate clock source might be different among
different Mediatek
SoCs. Either different clock ID or different intermediate frequency. I
want to keep
the flexibility of the driver so I am trying to specify the
intermediate clock source
in the device tree. I think I need to find out some other way to do it
since it's not
allowed to do it by creating a "cpufreq node" in device tree.

Thanks again for reviewing.

Best Regards,
Pi-Cheng

>
>> +       },
>> +       {}
>> +};
>> +MODULE_DEVICE_TABLE(of, mtk_cpufreq_match);
>> +
>> +static struct platform_driver mtk_cpufreq_platdrv = {
>> +       .driver = {
>> +               .name   = "mtk-cpufreq",
>> +               .of_match_table = mtk_cpufreq_match,
>> +       },
>> +       .probe  = mtk_cpufreq_probe,
>> +};
>> +module_platform_driver(mtk_cpufreq_platdrv);