From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thierry Reding Subject: Re: [TEGRA194_CPUFREQ Patch 1/3] firmware: tegra: adding function to get BPMP data Date: Tue, 7 Apr 2020 12:05:20 +0200 Message-ID: <20200407100520.GA1720957@ulmo> References: <1575394348-17649-1-git-send-email-sumitg@nvidia.com> <20191203174229.GA1721849@ulmo> <9404232d-84ce-a117-89dd-f2d8de80993e@kapsi.fi> <20191204091703.d32to5omdm3eynon@vireshk-i7> <20191204093339.GA2784830@ulmo> <20191204095138.rrul5vxnkprfwmku@vireshk-i7> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="C7zPtVaVf+AK4Oqc" Return-path: Content-Disposition: inline In-Reply-To: <20191204095138.rrul5vxnkprfwmku@vireshk-i7> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Rob Herring , Viresh Kumar , "Rafael J. Wysocki" Cc: Mikko Perttunen , Sumit Gupta , catalin.marinas-5wv7dgnIgG8@public.gmane.org, will-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, talho-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, linux-pm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, bbasu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, mperttunen-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-tegra@vger.kernel.org --C7zPtVaVf+AK4Oqc Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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. > >=20 > > 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. > >=20 > > 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. > >=20 > > 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. > >=20 > > Adding Rob and the device tree mailing list for feedback on this idea. >=20 > Took some time to find this thread, but something around this was > suggested by Rafael earlier. >=20 > https://lore.kernel.org/lkml/8139001.Q4eV8YG1Il-sKB8Sp2ER+y1GS7QM15AGw@public.gmane.org/ 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 { }; =20 cpus { + compatible =3D "nvidia,tegra194-ccplex"; + nvidia,bpmp =3D <&bpmp>; + #address-cells =3D <1>; #size-cells =3D <0>; =20 --- >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[] =3D { { .compatible =3D "nvidia,tegra194-ccplex", }, { /* sentinel */ } }; MODULE_DEVICE_TABLE(of, tegra194_cpufreq_of_match); static struct platform_driver tegra194_ccplex_driver =3D { .driver =3D { .name =3D "tegra194-cpufreq", .of_match_table =3D tegra194_cpufreq_of_match, }, .probe =3D tegra194_cpufreq_probe, .remove =3D 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. 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