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@xxxxxxxxxxxxxx/ 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. Thierry
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