Re: [RFC PATCH v2 20/35] ACPI: Rename acpi_processor_hotadd_init and remove pre-processor guards

[Russell King (Oracle)]

On Mon, Sep 18, 2023 at 03:50:09PM +1000, Gavin Shan wrote:
> 
> On 9/15/23 00:17, Jonathan Cameron wrote:
> > On Wed, 13 Sep 2023 16:38:08 +0000
> > James Morse <james.morse@xxxxxxx> wrote:
> > 
> > > acpi_processor_hotadd_init() will make a CPU present by mapping it
> > > based on its hardware id.
> > > 
> > > 'hotadd_init' is ambiguous once there are two different behaviours
> > > for cpu hotplug. This is for toggling the _STA present bit. Subsequent
> > > patches will add support for toggling the _STA enabled bit, named
> > > acpi_processor_make_enabled().
> > > 
> > > Rename it acpi_processor_make_present() to make it clear this is
> > > for CPUs that were not previously present.
> > > 
> > > Expose the function prototypes it uses to allow the preprocessor
> > > guards to be removed. The IS_ENABLED() check will let the compiler
> > > dead-code elimination pass remove this if it isn't going to be
> > > used.
> > > 
> > > Signed-off-by: James Morse <james.morse@xxxxxxx>
> > > ---
> > >   drivers/acpi/acpi_processor.c | 14 +++++---------
> > >   include/linux/acpi.h          |  2 --
> > >   2 files changed, 5 insertions(+), 11 deletions(-)
> > > 
> > > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > > index 75257fae10e7..22a15a614f95 100644
> > > --- a/drivers/acpi/acpi_processor.c
> > > +++ b/drivers/acpi/acpi_processor.c
> > > @@ -182,13 +182,15 @@ static void __init acpi_pcc_cpufreq_init(void) {}
> > >   #endif /* CONFIG_X86 */
> > >   /* Initialization */
> > > -#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
> > > -static int acpi_processor_hotadd_init(struct acpi_processor *pr)
> > > +static int acpi_processor_make_present(struct acpi_processor *pr)
> > >   {
> > >   	unsigned long long sta;
> > >   	acpi_status status;
> > >   	int ret;
> > > +	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU))
> > > +		return -ENODEV;
> > > +
> > >   	if (invalid_phys_cpuid(pr->phys_id))
> > >   		return -ENODEV;
> > > @@ -222,12 +224,6 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr)
> > >   	cpu_maps_update_done();
> > >   	return ret;
> > >   }
> > > -#else
> > > -static inline int acpi_processor_hotadd_init(struct acpi_processor *pr)
> > > -{
> > > -	return -ENODEV;
> > > -}
> > > -#endif /* CONFIG_ACPI_HOTPLUG_PRESENT_CPU */
> > >   static int acpi_processor_get_info(struct acpi_device *device)
> > >   {
> > > @@ -335,7 +331,7 @@ static int acpi_processor_get_info(struct acpi_device *device)
> > >   	 *  because cpuid <-> apicid mapping is persistent now.
> > >   	 */
> > >   	if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> > > -		int ret = acpi_processor_hotadd_init(pr);
> > > +		int ret = acpi_processor_make_present(pr);
> > >   		if (ret)
> > >   			return ret;
> > > diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> > > index 651dd43976a9..b7ab85857bb7 100644
> > > --- a/include/linux/acpi.h
> > > +++ b/include/linux/acpi.h
> > > @@ -316,12 +316,10 @@ static inline int acpi_processor_evaluate_cst(acpi_handle handle, u32 cpu,
> > >   }
> > >   #endif
> > > -#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
> > >   /* Arch dependent functions for cpu hotplug support */
> > >   int acpi_map_cpu(acpi_handle handle, phys_cpuid_t physid, u32 acpi_id,
> > >   		 int *pcpu);
> > >   int acpi_unmap_cpu(int cpu);
> > 
> > I've lost track somewhat but I think the definitions of these are still under ifdefs
> > which is messy if nothing else and might cause build issues.
> > 
> 
> Yup, it's not safe to use 'if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU))' in
> acpi_processor_make_present() until the ifdefs are removed for those two functions
> in individual architectures.

The same thing appears in a final patch that James seems to have added
to the repository:

ACPI: processor: Only call arch_unregister_cpu() if HOTPLUG_CPU is selected

in which acpi_processor_post_eject() has this change:

-       if (!device)
+       if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || !device)

I'm wondering if that's caused by a previous patch making the weak
definition of arch_unregister_cpu() dependent on HOTPLUG_CPU, and
whether dropping that ifdef around the function would be better. I
think I already asked that question, but this final patch seems to be
the confirmation that we need to provide a definition of it.

I think the reason James did it like that is because unregister_cpu()
is dependent upon CONFIG_HOTPLUG_CPU, but it's probably better to do:

#ifdef CONFIG_HOTPLUG_CPU
void __weak arch_unregister_cpu(int num)
{
	unregister_cpu(&per_cpu(cpu_devices, num));
}
#else
void __weak arch_unregister_cpu(int num)
{
}
#endif

Agreed?

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