Re: [PATCH -next] arm64: Export __cpu_logical_map

From: Sumit Gupta
Date: Tue Aug 11 2020 - 15:45:04 EST

ERROR: modpost: "__cpu_logical_map" [drivers/cpufreq/tegra194-cpufreq.ko] undefined!

ARM64 tegra194-cpufreq driver use cpu_logical_map, export
__cpu_logical_map to fix build issue.

I wonder why like other instances in the drivers, the mpidr is not get
directly from the cpu. The cpufreq_driver->init call happens when the cpu
is being brought online and is executed on the required cpu IIUC.

Yes, this occurs during hotplug case.
But in the case of system boot, 'cpufreq_driver->init' is called later
during cpufreq platform driver's probe. The value of CPU in 'policy->cpu'
can be different from the current CPU. That's why read_cpuid_mpidr() can't
be used.

Fair enough, why not do cross call like in set_target ? Since it is one-off
in init, I don't see any issue when you are doing it runtime for set_target.

read_cpuid_mpidr() is inline and avoids having to export the logical_cpu_map.
Though we may not add physical hotplug anytime soon, less dependency
on this cpu_logical_map is better given that we can resolve this without
the need to access the map.

To be honest, we have tried to remove all the dependency on cluster id
in generic code as it is not well defined. This one is tegra specific
driver so should be fine. But I am still bit nervous to export
cpu_logical_map as we have no clue what that would mean for physical

As suggested, I have done below change to get the cluster number using
read_cpuid_mpidr(). Please review and suggest if this looks ok?
I will send formal patch if the change is fine.

diff --git a/drivers/cpufreq/tegra194-cpufreq.c
index bae527e..06f5ccf 100644
--- a/drivers/cpufreq/tegra194-cpufreq.c
+++ b/drivers/cpufreq/tegra194-cpufreq.c
@@ -56,9 +56,11 @@ struct read_counters_work {

static struct workqueue_struct *read_counters_wq;

-static enum cluster get_cpu_cluster(u8 cpu)
+static void get_cpu_cluster(void *cluster)
- return MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
+ u64 mpidr = read_cpuid_mpidr() & MPIDR_HWID_BITMASK;
+ *((uint32_t *) cluster) = MPIDR_AFFINITY_LEVEL(mpidr, 1);

@@ -186,8 +188,10 @@ static unsigned int tegra194_get_speed(u32 cpu)
static int tegra194_cpufreq_init(struct cpufreq_policy *policy)
struct tegra194_cpufreq_data *data = cpufreq_get_driver_data();
- int cl = get_cpu_cluster(policy->cpu);
u32 cpu;
+ u32 cl;
+ smp_call_function_single(policy->cpu, get_cpu_cluster, &cl, true);

Thanks for this, looks good to me. You can add:

Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx>

I already merged Kefeng's __cpu_logical_map fix (commit eaecca9e7710)
but if the above goes in, I can drop the EXPORT_SYMBOL part (and keep
the rest as it's a good refactoring).

I have posted the formal patch.