From: Thierry Reding <thierry.reding@gmail.com>
To: Rob Herring <robh+dt@kernel.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Mikko Perttunen <cyndis@kapsi.fi>,
Sumit Gupta <sumitg@nvidia.com>,
catalin.marinas@arm.com, will@kernel.org, jonathanh@nvidia.com,
talho@nvidia.com, linux-pm@vger.kernel.org,
linux-tegra@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, bbasu@nvidia.com,
mperttunen@nvidia.com, devicetree@vger.kernel.org
Subject: Re: [TEGRA194_CPUFREQ Patch 1/3] firmware: tegra: adding function to get BPMP data
Date: Mon, 27 Apr 2020 09:18:00 +0200 [thread overview]
Message-ID: <20200427071800.GA3451400@ulmo> (raw)
In-Reply-To: <20200407100520.GA1720957@ulmo>
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On Tue, Apr 07, 2020 at 12:05:20PM +0200, Thierry Reding wrote:
> On Wed, Dec 04, 2019 at 03:21:38PM +0530, Viresh Kumar wrote:
> > On 04-12-19, 10:33, Thierry Reding wrote:
> > > Yeah, the code that registers this device is in drivers/base/cpu.c in
> > > register_cpu(). It even retrieves the device tree node for the CPU from
> > > device tree and stores it in cpu->dev.of_node, so we should be able to
> > > just pass &cpu->dev to tegra_bpmp_get() in order to retrieve a reference
> > > to the BPMP.
> > >
> > > That said, I'm wondering if perhaps we could just add a compatible
> > > string to the /cpus node for cases like this where we don't have an
> > > actual device representing the CPU complex. There are a number of CPU
> > > frequency drivers that register dummy devices just so that they have
> > > something to bind a driver to.
> > >
> > > If we allow the /cpus node to represent the CPU complex (if no other
> > > "device" does that yet), we can add a compatible string and have the
> > > cpufreq driver match on that.
> > >
> > > Of course this would be slightly difficult to retrofit into existing
> > > drivers because they'd need to remain backwards compatible with existing
> > > device trees. But it would allow future drivers to do this a little more
> > > elegantly. For some SoCs this may not matter, but especially once you
> > > start depending on additional resources this would come in handy.
> > >
> > > Adding Rob and the device tree mailing list for feedback on this idea.
> >
> > Took some time to find this thread, but something around this was
> > suggested by Rafael earlier.
> >
> > https://lore.kernel.org/lkml/8139001.Q4eV8YG1Il@vostro.rjw.lan/
>
> I gave this a try and came up with the following:
>
> --- >8 ---
> diff --git a/arch/arm64/boot/dts/nvidia/tegra194.dtsi b/arch/arm64/boot/dts/nvidia/tegra194.dtsi
> index f4ede86e32b4..e4462f95f0b3 100644
> --- a/arch/arm64/boot/dts/nvidia/tegra194.dtsi
> +++ b/arch/arm64/boot/dts/nvidia/tegra194.dtsi
> @@ -1764,6 +1764,9 @@ bpmp_thermal: thermal {
> };
>
> cpus {
> + compatible = "nvidia,tegra194-ccplex";
> + nvidia,bpmp = <&bpmp>;
> +
> #address-cells = <1>;
> #size-cells = <0>;
>
> --- >8 ---
>
> Now I can do something rougly like this, although I have a more complete
> patch locally that also gets rid of all the global variables because we
> now actually have a struct platform_device that we can anchor everything
> at:
>
> --- >8 ---
> static const struct of_device_id tegra194_cpufreq_of_match[] = {
> { .compatible = "nvidia,tegra194-ccplex", },
> { /* sentinel */ }
> };
> MODULE_DEVICE_TABLE(of, tegra194_cpufreq_of_match);
>
> static struct platform_driver tegra194_ccplex_driver = {
> .driver = {
> .name = "tegra194-cpufreq",
> .of_match_table = tegra194_cpufreq_of_match,
> },
> .probe = tegra194_cpufreq_probe,
> .remove = tegra194_cpufreq_remove,
> };
> module_platform_driver(tegra194_ccplex_driver);
> --- >8 ---
>
> I don't think that's exactly what Rafael (Cc'ed) had in mind, since the
> above thread seems to have mostly talked about binding a driver to each
> individual CPU.
>
> But this seems a lot better than having to instantiate a device from
> scratch just so that a driver can bind to it and it allows additional
> properties to be associated with the CCPLEX device.
>
> Rob, any thoughts on this from a device tree point of view? The /cpus
> bindings don't mention the compatible property, but there doesn't seem
> to be anything in the bindings that would prohibit its use.
>
> If we can agree on that, I can forward my local changes to Sumit for
> inclusion or reference.
Rob, do you see any reason why we shouldn't be able to use a compatible
string in the /cpus node for devices such as Tegra194 where there is no
dedicated hardware block for the CCPLEX?
Thierry
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next prev parent reply other threads:[~2020-04-27 7:18 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-03 17:32 [TEGRA194_CPUFREQ Patch 1/3] firmware: tegra: adding function to get BPMP data Sumit Gupta
2019-12-03 17:32 ` [TEGRA194_CPUFREQ Patch 2/3] cpufreq: Add Tegra194 cpufreq driver Sumit Gupta
2019-12-04 5:40 ` Viresh Kumar
2019-12-04 10:55 ` sumitg
2019-12-04 11:27 ` Viresh Kumar
2019-12-04 13:57 ` Dmitry Osipenko
2019-12-05 2:51 ` Viresh Kumar
2019-12-05 12:55 ` Dmitry Osipenko
2020-03-25 23:59 ` sumitg
2019-12-04 13:59 ` Dmitry Osipenko
2019-12-05 14:15 ` Dmitry Osipenko
2020-03-26 11:50 ` Viresh Kumar
2020-04-04 18:38 ` sumitg
2020-04-06 2:55 ` Viresh Kumar
2020-04-07 18:18 ` sumitg
2020-04-08 5:53 ` Viresh Kumar
2020-04-08 11:24 ` sumitg
2020-04-09 7:44 ` Viresh Kumar
2020-04-09 11:21 ` Sumit Gupta
2020-04-13 6:21 ` Viresh Kumar
2020-04-13 12:20 ` Sumit Gupta
2020-04-14 5:45 ` Viresh Kumar
2020-04-15 11:25 ` Sumit Gupta
2020-04-16 3:37 ` Viresh Kumar
2020-04-16 7:06 ` Sumit Gupta
2019-12-03 17:32 ` [TEGRA194_CPUFREQ Patch 3/3] arm64: defconfig: Enable CONFIG_ARM_TEGRA194_CPUFREQ Sumit Gupta
2019-12-03 17:42 ` [TEGRA194_CPUFREQ Patch 1/3] firmware: tegra: adding function to get BPMP data Thierry Reding
2019-12-04 8:45 ` Mikko Perttunen
2019-12-04 9:17 ` Viresh Kumar
2019-12-04 9:33 ` Thierry Reding
2019-12-04 9:51 ` Viresh Kumar
2020-04-07 10:05 ` Thierry Reding
2020-04-27 7:18 ` Thierry Reding [this message]
2020-04-29 8:21 ` Sumit Gupta
2020-05-06 16:58 ` Thierry Reding
2020-05-20 14:43 ` Rob Herring
2020-05-20 15:38 ` Thierry Reding
2020-05-20 16:21 ` Rob Herring
2019-12-04 10:21 ` Mikko Perttunen
2019-12-04 10:26 ` Viresh Kumar
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