OK, I think I found out the way. Would this be correct?
-----------------------------------------------------------------------------------------------
extern struct cpu_topology cpu_topology[NR_CPUS];

static struct device *qcom_cpufreq_kryo_get_cluster_lead(int cluster)
{
	unsigned cpu;

	for_each_possible_cpu(cpu) {
		if ((cluster == cpu_topology[cpu].cluster_id) &&
			(0 == cpu_topology[cpu].core_id))
			return get_cpu_device(cpu);
	}

	return NULL;
}
-----------------------------------------------------------------------------------------------

-----Original Message-----
From: ilialin at codeaurora.org <redacted>
Sent: Tuesday, May 22, 2018 09:56
To: 'Sudeep Holla' <redacted>; 'mturquette at baylibre.com'
[off-list ref]; 'sboyd at kernel.org' [off-list ref];
'robh at kernel.org' [off-list ref]; 'mark.rutland at arm.com'
[off-list ref]; 'viresh.kumar at linaro.org'
[off-list ref]; 'nm at ti.com' [off-list ref];
'lgirdwood at gmail.com' [off-list ref]; 'broonie at kernel.org'
[off-list ref]; 'andy.gross at linaro.org' [off-list ref];
'david.brown at linaro.org' [off-list ref];
'catalin.marinas at arm.com' [off-list ref];
'will.deacon at arm.com' [off-list ref]; 'rjw at rjwysocki.net'
[off-list ref]; 'linux-clk at vger.kernel.org' <linux-
clk at vger.kernel.org>
Cc: 'devicetree at vger.kernel.org' <redacted>; 'linux-
kernel at vger.kernel.org' [off-list ref]; 'linux-
pm at vger.kernel.org' [off-list ref]; 'linux-arm-
msm at vger.kernel.org' [off-list ref]; 'linux-
soc at vger.kernel.org' [off-list ref]; 'linux-arm-
kernel at lists.infradead.org' [off-list ref];
'rnayak at codeaurora.org' [off-list ref];
'amit.kucheria at linaro.org' [off-list ref];
'nicolas.dechesne at linaro.org' [off-list ref];
'celster at codeaurora.org' [off-list ref];
'tfinkel at codeaurora.org' [off-list ref]
Subject: RE: [PATCH] cpufreq: Add Kryo CPU scaling driver

quoted

-----Original Message-----
From: Sudeep Holla <redacted>
Sent: Monday, May 21, 2018 16:05
To: ilialin at codeaurora.org; mturquette at baylibre.com; sboyd at kernel.org;
robh at kernel.org; mark.rutland at arm.com; viresh.kumar at linaro.org;
nm at ti.com; lgirdwood at gmail.com; broonie at kernel.org;
andy.gross at linaro.org; david.brown at linaro.org;
catalin.marinas at arm.com; will.deacon at arm.com; rjw at rjwysocki.net;
linux-clk at vger.kernel.org
Cc: Sudeep Holla <redacted>; devicetree at vger.kernel.org;
linux-kernel at vger.kernel.org; linux-pm at vger.kernel.org; linux-arm-
msm at vger.kernel.org; linux-soc at vger.kernel.org; linux-arm-
kernel at lists.infradead.org; rnayak at codeaurora.org;
amit.kucheria at linaro.org; nicolas.dechesne at linaro.org;
celster at codeaurora.org; tfinkel at codeaurora.org
Subject: Re: [PATCH] cpufreq: Add Kryo CPU scaling driver



On 21/05/18 13:57, ilialin at codeaurora.org wrote:

quoted

[...]

quoted

quoted

quoted

+#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.

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 = <2>;
	#size-cells = <0>;

	CPU0: cpu at 0 {
		...
		reg = <0x0 0x0>;
		...
	};

	CPU1: cpu at 1 {
		...
		reg = <0x0 0x1>;
		...
	};

	CPU2: cpu at 100 {
		...
		reg = <0x0 0x100>;
		...
	};

	CPU3: cpu at 101 {
		...
		reg = <0x0 0x101>;
		...
	};

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

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

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

			core1 {
				cpu = <&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?

quoted

--
Regards,
Sudeep