linux-kernel - Re: [PATCH 1/2] acpi: cppc: add cpufreq device

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Date:   Thu, 10 Dec 2020 15:02:23 +0000
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Mian Yousaf Kaukab <yousaf.kaukab@...e.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Mian Yousaf Kaukab <ykaukab@...e.de>,
        Petr Cervinka <pcervinka@...e.com>
Subject: Re: [PATCH 1/2] acpi: cppc: add cpufreq device

Hi guys,

On Thursday 10 Dec 2020 at 15:32:09 (+0100), Rafael J. Wysocki wrote:
> On Thu, Dec 10, 2020 at 3:23 PM Mian Yousaf Kaukab
> <yousaf.kaukab@...e.com> wrote:
> >
> > From: Mian Yousaf Kaukab <ykaukab@...e.de>
> >
> > Since commit 28f06f770454 ("cppc_cpufreq: replace per-cpu structures with
> > lists"), cppc-cpufreq driver doesn't check availability of PSD data before
> > registering with cpufreq core. As a result on a ThunderX2 platform when
> > CPPC is disabled from BIOS, kernel log is spammed with following messages:
> >
> > [  180.974166] CPPC Cpufreq: Error in acquiring _CPC/_PSD data for CPUxx
> >
> > acpi_cppc_processor_probe() never succeed in this case because
> > acpi_evaluate_object_typed("_CPC") always returns AE_NOT_FOUND. When
> > cpufreq core calls cppc_cpufreq_cpu_init(), driver fails to obtain PSD data
> > and print error messages.
> >
> > Convert cppc-cpufreq driver to a platform driver (done in a separate patch)
> > and add cppc-cpufreq device when acpi_cppc_processor_probe() succeeds.
> 
> Honestly, I prefer to drop 28f06f770454 (along with its follower)
> instead of making this change.
> 
> > Fixes: 28f06f770454 ("cppc_cpufreq: replace per-cpu structures with lists")
> 

Sorry for introducing this, I though it was enough to bail out of cpu
init if _CPC entries are not present.

I'll defer to Rafael to decide whether to drop the patches or accept
alternative fixes, but I believe the rework of the data structures and
initialisation is useful.

As alternative fix, would it be okay to introduce a check function to
verify for !cpc_ptr, to be called in cppc_cpufreq_init()? In that case
the driver would not be registered if this check fails.

Thanks,
Ionela.

> Thanks!