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From: Sudeep Holla <sudeep.holla@arm.com>
To: Sumit Gupta <sumitg@nvidia.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mikko Perttunen <mperttunen@nvidia.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Hulk Robot <hulkci@huawei.com>,
	"linux-kernel@vger.kernel.org List"
	<linux-kernel@vger.kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	Bibek Basu <bbasu@nvidia.com>,
	Sudeep Holla <sudeep.holla@arm.com>
Subject: Re: [PATCH -next] arm64: Export __cpu_logical_map
Date: Mon, 27 Jul 2020 17:05:15 +0100	[thread overview]
Message-ID: <20200727160515.GA8003@bogus> (raw)
In-Reply-To: <00cf6e67-16ed-872d-2c16-0ceea6b6f514@nvidia.com>

On Sun, Jul 26, 2020 at 05:16:27PM +0530, Sumit Gupta wrote:
> > > > ERROR: modpost: "__cpu_logical_map" [drivers/cpufreq/tegra194-cpufreq.ko] undefined!
> > > >
> > > > ARM64 tegra194-cpufreq driver use cpu_logical_map, export
> > > > __cpu_logical_map to fix build issue.
> > > >
> >
> > I wonder why like other instances in the drivers, the mpidr is not get
> > directly from the cpu. The cpufreq_driver->init call happens when the cpu
> > is being brought online and is executed on the required cpu IIUC.
> >
> Yes, this occurs during hotplug case.
> But in the case of system boot, 'cpufreq_driver->init' is called later
> during cpufreq platform driver's probe. The value of CPU in 'policy->cpu'
> can be different from the current CPU. That's why read_cpuid_mpidr() can't
> be used.
>

Fair enough, why not do cross call like in set_target ? Since it is one-off
in init, I don't see any issue when you are doing it runtime for set_target.

> > read_cpuid_mpidr() is inline and avoids having to export the logical_cpu_map.
> > Though we may not add physical hotplug anytime soon, less dependency
> > on this cpu_logical_map is better given that we can resolve this without
> > the need to access the map.
> >

To be honest, we have tried to remove all the dependency on cluster id
in generic code as it is not well defined. This one is tegra specific
driver so should be fine. But I am still bit nervous to export
cpu_logical_map as we have no clue what that would mean for physical
hotplug.


--
Regards,
Sudeep

WARNING: multiple messages have this Message-ID
From: Sudeep Holla <sudeep.holla@arm.com>
To: Sumit Gupta <sumitg@nvidia.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	"linux-kernel@vger.kernel.org List"
	<linux-kernel@vger.kernel.org>,
	Mikko Perttunen <mperttunen@nvidia.com>,
	Hulk Robot <hulkci@huawei.com>, Bibek Basu <bbasu@nvidia.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH -next] arm64: Export __cpu_logical_map
Date: Mon, 27 Jul 2020 17:05:15 +0100	[thread overview]
Message-ID: <20200727160515.GA8003@bogus> (raw)
In-Reply-To: <00cf6e67-16ed-872d-2c16-0ceea6b6f514@nvidia.com>

On Sun, Jul 26, 2020 at 05:16:27PM +0530, Sumit Gupta wrote:
> > > > ERROR: modpost: "__cpu_logical_map" [drivers/cpufreq/tegra194-cpufreq.ko] undefined!
> > > >
> > > > ARM64 tegra194-cpufreq driver use cpu_logical_map, export
> > > > __cpu_logical_map to fix build issue.
> > > >
> >
> > I wonder why like other instances in the drivers, the mpidr is not get
> > directly from the cpu. The cpufreq_driver->init call happens when the cpu
> > is being brought online and is executed on the required cpu IIUC.
> >
> Yes, this occurs during hotplug case.
> But in the case of system boot, 'cpufreq_driver->init' is called later
> during cpufreq platform driver's probe. The value of CPU in 'policy->cpu'
> can be different from the current CPU. That's why read_cpuid_mpidr() can't
> be used.
>

Fair enough, why not do cross call like in set_target ? Since it is one-off
in init, I don't see any issue when you are doing it runtime for set_target.

> > read_cpuid_mpidr() is inline and avoids having to export the logical_cpu_map.
> > Though we may not add physical hotplug anytime soon, less dependency
> > on this cpu_logical_map is better given that we can resolve this without
> > the need to access the map.
> >

To be honest, we have tried to remove all the dependency on cluster id
in generic code as it is not well defined. This one is tegra specific
driver so should be fine. But I am still bit nervous to export
cpu_logical_map as we have no clue what that would mean for physical
hotplug.


--
Regards,
Sudeep

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2020-07-27 16:05 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200724030433.22287-1-wangkefeng.wang@huawei.com>
2020-07-24  3:08 ` Kefeng Wang
2020-07-24  3:08   ` Kefeng Wang
2020-07-24  8:16   ` Anshuman Khandual
2020-07-24  8:16     ` Anshuman Khandual
2020-07-24  9:13     ` Mark Rutland
2020-07-24  9:13       ` Mark Rutland
2020-07-24  9:35       ` Catalin Marinas
2020-07-24  9:35         ` Catalin Marinas
2020-07-24 10:33         ` Anshuman Khandual
2020-07-24 10:33           ` Anshuman Khandual
2020-07-24  9:16     ` Kefeng Wang
2020-07-24  9:16       ` Kefeng Wang
2020-07-24  9:30     ` Catalin Marinas
2020-07-24  9:30       ` Catalin Marinas
2020-07-24 10:36       ` Anshuman Khandual
2020-07-24 10:36         ` Anshuman Khandual
2020-07-24  9:43   ` Christoph Hellwig
2020-07-24  9:43     ` Christoph Hellwig
2020-07-24 13:10   ` Sudeep Holla
2020-07-24 13:10     ` Sudeep Holla
2020-07-25  2:00     ` Kefeng Wang
2020-07-25  2:00       ` Kefeng Wang
2020-07-26 11:46     ` Sumit Gupta
2020-07-26 11:46       ` Sumit Gupta
2020-07-27 16:05       ` Sudeep Holla [this message]
2020-07-27 16:05         ` Sudeep Holla
2020-08-01 12:16         ` Sumit Gupta
2020-08-01 12:16           ` Sumit Gupta
2020-08-10  7:49           ` Sudeep Holla
2020-08-10  7:49             ` Sudeep Holla
2020-08-10 10:19             ` Catalin Marinas
2020-08-10 10:19               ` Catalin Marinas
2020-08-10 12:11               ` Sudeep Holla
2020-08-10 12:11                 ` Sudeep Holla
2020-08-11 19:44               ` Sumit Gupta
2020-08-11 19:44                 ` Sumit Gupta

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