linux-kernel - Re: [PATCH v3 21/22] cpufreq: add support for CPU DVFS based on SCMI message protocol

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Date:   Thu, 5 Oct 2017 13:20:11 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     ALKML <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Roy Franz <roy.franz@...ium.com>,
        Harb Abdulhamid <harba@...eaurora.org>,
        Nishanth Menon <nm@...com>, Loc Ho <lho@....com>,
        Alexey Klimov <alexey.klimov@....com>,
        Ryan Harkin <Ryan.Harkin@....com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 21/22] cpufreq: add support for CPU DVFS based on SCMI
 message protocol

On Wed, Oct 4, 2017 at 5:01 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>>> +
>>> +static struct platform_driver scmi_cpufreq_platdrv = {
>>> +       .driver = {
>>> +               .name   = "scmi-cpufreq",
>>> +       },
>>> +       .probe          = scmi_cpufreq_probe,
>>> +       .remove         = scmi_cpufreq_remove,
>>> +};
>>
>> You appear to have split this driver into the 'cpufreq' side and
>> the 'protocol' handler in a different file. I already commented that
>> the way the main scmi driver knows about all the protocols looks
>> bad, here we can see another aspect of the same problem.
>>
>> Rather than manually register a platform_device for the purpose
>> of connecting it to the cpufreq driver, there should be a way
>> to dynamically register the protocol from the cpufreq driver
>> and then have both in the same file.
>>
>
> I agree that should be possible. I took this approach for 2 reasons:
>
> 1. to avoid all sorts of probe ordering issues
> 2. we may have system with multiple instances of SCMI. E.g. a system
>    may have multiple remote processors, each controlling dvfs/power mgmt
>    of a subset of CPUs/devices controller in OS.
>
> I have to admit that I haven't thought too much in details yet. That's
> the main idea behind scmi_handle and restricting access to that only to
> sub-nodes in it. I am open to suggestions.

How about introducing a separate bus_type for protocols?
The platform_device you use here isn't really the best abstraction,
and with a new bus_type, you can handle multiple instances of
scmi as well as decoupling them from the protocol drivers.

      Arnd