linux-kernel - Re: [PATCH] cpufreq: Register cpufreq drivers only after CPU devices are registered

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Message-ID: <20191114084327.ra5hnpizeffxzis2@vireshk-i7>
Date:   Thu, 14 Nov 2019 14:13:27 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: Register cpufreq drivers only after CPU devices
 are registered

On 14-11-19, 09:40, Rafael J. Wysocki wrote:
> On Thu, Nov 14, 2019 at 4:36 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > The cpufreq core heavily depends on the availability of the struct
> > device for CPUs and if they aren't available at the time cpufreq driver
> > is registered, we will never succeed in making cpufreq work.
> >
> > This happens due to following sequence of events:
> >
> > - cpufreq_register_driver()
> >   - subsys_interface_register()
> >   - return 0; //successful registration of driver
> >
> > ... at a later point of time
> >
> > - register_cpu();
> >   - device_register();
> >     - bus_probe_device();
> >       - sif->add_dev();
> >         - cpufreq_add_dev();
> >           - get_cpu_device(); //FAILS
> >   - per_cpu(cpu_sys_devices, num) = &cpu->dev; //used by get_cpu_device()
> >   - return 0; //CPU registered successfully
> >
> > Because the per-cpu variable cpu_sys_devices is set only after the CPU
> > device is regsitered, cpufreq will never be able to get it when
> > cpufreq_add_dev() is called.
> >
> > This patch avoids this failure by making sure device structure of at
> > least CPU0 is available when the cpufreq driver is registered, else
> > return -EPROBE_DEFER.
> >
> > Reported-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > Signed-off-by: Amit Kucheria <amit.kucheria@...aro.org>
> > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> > ---
> > @Amit: I have added your sob without asking as you were involved in
> > getting us to this patch, you did a lot of testing yesterday to find the
> > root cause.
> 
> Co-developed-by is for that, so I used it in the commit.
> 
> > @Rafael: This fixes the issues reported by Bjorn on Amit's series and so
> > should land before Amit's series, if at all this is acceptable to you.
> 
> Well, yes it is.
> 
> Applied for 5.5 with a reworded subject, thanks!

Thanks.

-- 
viresh