Re: [PATCH -next] arm64: Export __cpu_logical_map

Sumit Gupta
2020-08-01T12:19:08Z

>>>>> 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
> hotplug.
>
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.

Thanks,
Sumit

----

diff --git a/drivers/cpufreq/tegra194-cpufreq.c
b/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);

>
> --
> Regards,
> Sudeep