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Subject: RE: [PATCH] cpufreq: Add Kryo CPU scaling driver
Date:   Tue, 22 May 2018 09:56:19 +0300
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> -----Original Message-----
> From: Sudeep Holla <sudeep.holla@arm.com>
> Sent: Monday, May 21, 2018 16:05
> To: ilialin@codeaurora.org; mturquette@baylibre.com; sboyd@kernel.org;
> robh@kernel.org; mark.rutland@arm.com; viresh.kumar@linaro.org;
> nm@ti.com; lgirdwood@gmail.com; broonie@kernel.org;
> andy.gross@linaro.org; david.brown@linaro.org; =
catalin.marinas@arm.com;
> will.deacon@arm.com; rjw@rjwysocki.net; linux-clk@vger.kernel.org
> Cc: Sudeep Holla <sudeep.holla@arm.com>; devicetree@vger.kernel.org;
> linux-kernel@vger.kernel.org; linux-pm@vger.kernel.org; linux-arm-
> msm@vger.kernel.org; linux-soc@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; rnayak@codeaurora.org;
> amit.kucheria@linaro.org; nicolas.dechesne@linaro.org;
> celster@codeaurora.org; tfinkel@codeaurora.org
> Subject: Re: [PATCH] cpufreq: Add Kryo CPU scaling driver
>=20
>=20
>=20
> On 21/05/18 13:57, ilialin@codeaurora.org wrote:
> >
> [...]
>=20
> >>> +#include <linux/cpu.h>
> >>> +#include <linux/err.h>
> >>> +#include <linux/init.h>
> >>> +#include <linux/kernel.h>
> >>> +#include <linux/module.h>
> >>> +#include <linux/nvmem-consumer.h>
> >>> +#include <linux/of.h>
> >>> +#include <linux/platform_device.h>
> >>> +#include <linux/pm_opp.h>
> >>> +#include <linux/slab.h>
> >>> +#include <linux/soc/qcom/smem.h>
> >>> +
> >>> +#define MSM_ID_SMEM	137
> >>> +#define SILVER_LEAD	0
> >>> +#define GOLD_LEAD	2
> >>> +
> >>
> >> So I gather form other emails, that these are physical cpu =
number(not
> >> even unique identifier like MPIDR). Will this work on parts or
> >> platforms that need to boot in GOLD LEAD cpus.
> >
> > The driver is for Kryo CPU, which (and AFAIK all multicore MSMs)
> > always boots on the CPU0.
>=20
>=20
> That may be true and I am not that bothered about it. But assuming =
physical
> ordering from the logical cpu number is *incorrect* and will break if =
kernel
> decides to change the allocation algorithm. Kernel provides no =
guarantee on
> that, so you need to depend on some physical ID or may be DT to =
achieve
> what your want. But the current code as it stands is wrong.

Got your point. In fact CPUs are numbered 0-3 and ordered into 2 =
clusters in the DT:

cpus {
	#address-cells =3D <2>;
	#size-cells =3D <0>;

	CPU0: cpu@0 {
		...
		reg =3D <0x0 0x0>;
		...
	};

	CPU1: cpu@1 {
		...
		reg =3D <0x0 0x1>;
		...
	};

	CPU2: cpu@100 {
		...
		reg =3D <0x0 0x100>;
		...
	};

	CPU3: cpu@101 {
		...
		reg =3D <0x0 0x101>;
		...
	};

	cpu-map {
		cluster0 {
			core0 {
				cpu =3D <&CPU0>;
			};

			core1 {
				cpu =3D <&CPU1>;
			};
		};

		cluster1 {
			core0 {
				cpu =3D <&CPU2>;
			};

			core1 {
				cpu =3D <&CPU3>;
			};
		};
	};
};

As far, as I understand, they are probed in the same order. However, to =
be certain that the physical CPU is the one I intend to configure, I =
have to fetch the device structure pointer for the cpu-map -> clusterX =
-> core0 -> cpu path. Could you suggest a kernel API to do that?


>=20
> --
> Regards,
> Sudeep