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    SubjectRe: [PATCH v4 3/4] scmi-cpufreq: get opp_shared_cpus from opp-v2 for EM
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    Hi All, thanks for your feedback, please see below

    On 12/8/20 12:22 PM, Sudeep Holla wrote:
    > On Tue, Dec 08, 2020 at 11:34:36AM +0000, Lukasz Luba wrote:
    >>
    >>
    >> On 12/8/20 11:20 AM, Sudeep Holla wrote:
    >>> On Tue, Dec 08, 2020 at 12:56:11PM +0530, Viresh Kumar wrote:
    >>>> On 08-12-20, 07:22, Nicola Mazzucato wrote:
    >>>>> On 12/8/20 5:50 AM, Viresh Kumar wrote:
    >>>>>> On 02-12-20, 17:23, Nicola Mazzucato wrote:
    >>>>>>> nr_opp = dev_pm_opp_get_opp_count(cpu_dev);
    >>>>>>> if (nr_opp <= 0) {
    >>>>>>> - dev_dbg(cpu_dev, "OPP table is not ready, deferring probe\n");
    >>>>>>> - ret = -EPROBE_DEFER;
    >>>>>>> - goto out_free_opp;
    >>>>>>> + ret = handle->perf_ops->device_opps_add(handle, cpu_dev);
    >>>>>>> + if (ret) {
    >>>>>>> + dev_warn(cpu_dev, "failed to add opps to the device\n");
    >>>>>>> + goto out_free_cpumask;
    >>>>>>> + }
    >>>>>>> +
    >>>>>>> + ret = dev_pm_opp_set_sharing_cpus(cpu_dev, opp_shared_cpus);
    >>>>>>> + if (ret) {
    >>>>>>> + dev_err(cpu_dev, "%s: failed to mark OPPs as shared: %d\n",
    >>>>>>> + __func__, ret);
    >>>>>>> + goto out_free_cpumask;
    >>>>>>> + }
    >>>>>>> +
    >>>>>>
    >>>>>> Why do we need to call above two after calling
    >>>>>> dev_pm_opp_get_opp_count() ?
    >>>>>
    >>>>> Sorry, I am not sure to understand your question here. If there are no opps for
    >>>>> a device we want to add them to it
    >>>>
    >>>> Earlier we used to call handle->perf_ops->device_opps_add() and
    >>>> dev_pm_opp_set_sharing_cpus() before calling dev_pm_opp_get_opp_count(), why is
    >>>> the order changed now ?
    >>>>
    >>>>
    >>>> I am not sure why they would be duplicated in your case. I though
    >>>> device_opps_add() is responsible for dynamically adding the OPPs here.
    >>>>
    >>>
    >>> It is because of per-CPU vs per domain drama here. Imagine a system with
    >>> 4 CPUs which the firmware puts in individual domains while they all are
    >>> in the same perf domain and hence OPP is marked shared in DT.
    >>>
    >>> Since this probe gets called for all the cpus, we need to skip adding
    >>> OPPs for the last 3(add only for 1st one and mark others as shared).
    >>> If we attempt to add OPPs on second cpu probe, it *will* shout as duplicate
    >>> OPP as we would have already marked it as shared table with the first cpu.
    >>> Am I missing anything ? I suggested this as Nicola saw OPP duplicate
    >>> warnings when he was hacking up this patch.
    >>>
    >>>>> otherwise no need as they would be duplicated.
    >>>>>> And we don't check the return value of
    >>>>>> the below call anymore, moreover we have to call it twice now.
    >>>
    >>> Yes, that looks wrong, we need to add the check for non zero values, but ....

    will add the check, thanks

    >>>
    >>>>>
    >>>>> This second get_opp_count is required such that we register em with the correct
    >>>>> opp number after having added them. Without this the opp_count would not be correct.
    >>>>
    >>>
    >>> ... I have a question here. Why do you need to call
    >>>
    >>> em_dev_register_perf_domain(cpu_dev, nr_opp, &em_cb, opp_shared_cpus..)
    >>>
    >>> on each CPU ? Why can't that be done once for unique opp_shared_cpus ?

    I left it untouched to reduce changes, but I see your point.

    >>
    >> It just have to be called once, for one CPU from the mask. Otherwise for
    >> the next CPUs you should see error:
    >> "EM: exists for CPU%d"
    >
    > OK cool, at least it is designed and expected to be used like I thought.
    > Ah, I might have seen those, but never thought it was error message 😄
    >
    >> It can happen that this print is not seen when the get_cpu_device(cpu)
    >> failed, but that would lead to investigation why CPU devices are not
    >> there yet.
    >>
    >> Nicola: have you seen that print?
    >>
    >
    > I assume you must see that and you need to pull this inside if condition
    > to do this once for each performance domain.

    I don't see that error, and that's also why I left it there. If there's already
    and em_pd for a device, EM just returns with an error that we don't check.

    I agree that it makes more sense to register em for opp_shared_cpus.

    >
    > --
    > Regards,
    > Sudeep
    >

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