Re: [PATCH 1/2] powerpc: export the CPU node count

[Laurent Dufour <ldufour@linux.ibm.com>]

On 07/11/2022 13:11:17, Nicholas Piggin wrote:
> On Sat Oct 29, 2022 at 2:00 AM AEST, Laurent Dufour wrote:
>> At boot time, the FDT is parsed to compute the number of CPUs.
>> In addition count the number of CPU nodes and export it.
>>
>> This is useful when building the FDT for a kexeced kernel since we need to
>> take in account the CPU node added since the boot time during CPU hotplug
>> operations.
> 
> It would be nice if it just realloced memory in this case, but that
> looks like a bigger change.

I agree, and I think the best option in long term would be the series 
Sourabh Jain sent in June, updating the crash kernel FDT without reloading
it (https://lore.kernel.org/linuxppc-dev/20220620070106.93141-1-sourabhjain@linux.ibm.com/)

In the meantime, this solves the issue.

> 
> But these patches look okay to me, if you can solve the compile bug.

Indeed, the compile bugs are raised because I added the definition of the new variable 
'boot_cpu_node_count' in kexec_ranges.h, and add the inclusion of that file in prom.c.

I was not confident putting this new variable definition in that header file, but I 
didn't find a better option.

Do you have a better idea of header file to use?

Could I just declare this variable "extern" in arch/powerpc/kexec/file_load_64.c? This looks
ugly to me.

Thanks,
Laurent.


> Thanks,
> Nick
> 
>>
>> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
>> ---
>>  arch/powerpc/include/asm/kexec_ranges.h | 2 ++
>>  arch/powerpc/kernel/prom.c              | 4 ++++
>>  2 files changed, 6 insertions(+)
>>
>> diff --git a/arch/powerpc/include/asm/kexec_ranges.h b/arch/powerpc/include/asm/kexec_ranges.h
>> index f83866a19e87..bf35d00ddd09 100644
>> --- a/arch/powerpc/include/asm/kexec_ranges.h
>> +++ b/arch/powerpc/include/asm/kexec_ranges.h
>> @@ -22,4 +22,6 @@ int add_rtas_mem_range(struct crash_mem **mem_ranges);
>>  int add_opal_mem_range(struct crash_mem **mem_ranges);
>>  int add_reserved_mem_ranges(struct crash_mem **mem_ranges);
>>  
>> +extern unsigned int boot_cpu_node_count;
>> +
>>  #endif /* _ASM_POWERPC_KEXEC_RANGES_H */
>> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
>> index 1eed87d954ba..d326148fd5a4 100644
>> --- a/arch/powerpc/kernel/prom.c
>> +++ b/arch/powerpc/kernel/prom.c
>> @@ -56,6 +56,7 @@
>>  #include <asm/drmem.h>
>>  #include <asm/ultravisor.h>
>>  #include <asm/prom.h>
>> +#include <asm/kexec_ranges.h>
>>  
>>  #include <mm/mmu_decl.h>
>>  
>> @@ -72,6 +73,7 @@ int __initdata iommu_is_off;
>>  int __initdata iommu_force_on;
>>  unsigned long tce_alloc_start, tce_alloc_end;
>>  u64 ppc64_rma_size;
>> +unsigned int boot_cpu_node_count __ro_after_init;
>>  #endif
>>  static phys_addr_t first_memblock_size;
>>  static int __initdata boot_cpu_count;
>> @@ -335,6 +337,8 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
>>  	if (type == NULL || strcmp(type, "cpu") != 0)
>>  		return 0;
>>  
>> +	boot_cpu_node_count++;
>> +
>>  	/* Get physical cpuid */
>>  	intserv = of_get_flat_dt_prop(node, "ibm,ppc-interrupt-server#s", &len);
>>  	if (!intserv)
>> -- 
>> 2.38.1
>