Re: [PATCH] powerpc: Adjust config HOTPLUG_CPU dependency

[Vishal Chourasia <vishalc@linux.ibm.com>]

On 22/11/23 3:03 pm, Aneesh Kumar K V wrote:
> On 11/22/23 2:53 PM, Vishal Chourasia wrote:
>> Changed HOTPLUG_CPU dependency to SMP and either ARCH_HIBERNATION_POSSIBLE or
>> ARCH_SUSPEND_POSSIBLE, aligning with systems' suspend/hibernation capabilities.
>> This update links CPU hotplugging more logically with platforms' capabilities.
>>
>> Other changes include
>>
>> 1. configs ARCH_HIBERNATION_POSSIBLE and ARCH_SUSPEND_POSSIBLE are now selected
>>    only if required platform dependencies are met.
>>
>> 2. Defaults for configs ARCH_HIBERNATION_POSSIBLE and
>>    ARCH_SUSPEND_POSSIBLE has been set to 'N'
>>
>> Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
>> Suggested-by: Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>
>> Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
>> Signed-off-by: Vishal Chourasia <vishalc@linux.ibm.com>
>>
>> v1: https://lore.kernel.org/all/20231114082046.6018-1-vishalc@linux.ibm.com
>> ---
>> During the configuration process with 'make randconfig' followed by
>> 'make olddefconfig', we observed a warning indicating an unmet direct
>> dependency for the HOTPLUG_CPU option. The dependency in question relates to
>> various PowerPC configurations (PPC_PSERIES, PPC_PMAC, PPC_POWERNV,
>> FSL_SOC_BOOKE) which were not enabled, yet the HOTPLUG_CPU was being
>> erroneously selected due to an implicit assumption by the PM_SLEEP_SMP option.
>> This misalignment in dependencies could potentially lead to inconsistent kernel
>> configuration states, especially when considering the necessary hardware
>> support for CPU hot-plugging on PowerPC platforms. The patch aims to correct
>> this by ensuring that ARCH_HIBERNATION_POSSIBLE is contingent upon the
>> appropriate PowerPC configurations being active.
>>
>> steps to reproduce (before applying the patch):
>>
>> Run 'make pseries_le_defconfig'
>> Run 'make menuconfig'
>> Enable hibernation [ Kernel options -> Hibernation (aka 'suspend to disk') ] 
>> Disable [ Platform support -> IBM PowerNV (Non-Virtualized) platform support ]
>> Disable [ Platform support -> IBM pSeries & new (POWER5-based) iSeries ]
>> Enable SMP [ Processor support -> Symmetric multi-processing support ]
>> Save the config
>> Run 'make olddefconfig'
>>
>>  arch/powerpc/Kconfig | 13 +++++--------
>>  1 file changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index 6f105ee4f3cf..6e7e9af2f0c1 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -155,6 +155,8 @@ config PPC
>>  	select ARCH_HAS_TICK_BROADCAST		if GENERIC_CLOCKEVENTS_BROADCAST
>>  	select ARCH_HAS_UACCESS_FLUSHCACHE
>>  	select ARCH_HAS_UBSAN_SANITIZE_ALL
>> +	select ARCH_HIBERNATION_POSSIBLE        if (PPC_PSERIES || PPC_PMAC || PPC_POWERNV || FSL_SOC_BOOKE)
>> +	select ARCH_SUSPEND_POSSIBLE            if (ADB_PMU || PPC_EFIKA || PPC_LITE5200 || PPC_83xx || (PPC_85xx && !PPC_E500MC) || PPC_86xx || PPC_PSERIES || 44x || 40x)
> We should keep that sorted as explained in comment around that. 
Sure. I will send out another patch
>
>>  	select ARCH_HAVE_NMI_SAFE_CMPXCHG
>>  	select ARCH_KEEP_MEMBLOCK
>>  	select ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE	if PPC_RADIX_MMU
>> @@ -380,14 +382,10 @@ config DEFAULT_UIMAGE
>>  	  Used to allow a board to specify it wants a uImage built by default
>>  
>>  config ARCH_HIBERNATION_POSSIBLE
>> -	bool
>> -	default y
>> +	def_bool n
>
> We should be able to keep this 
> config ARCH_HIBERNATION_POSSIBLE
>     bool
>
>
> That is how we have rest of the ARCH_* config. I am not sure we need to explicitly say "def_bool n" 
I believed it improves readability, that all. I can revert it back.
>
>>  
>>  config ARCH_SUSPEND_POSSIBLE
>> -	def_bool y
>> -	depends on ADB_PMU || PPC_EFIKA || PPC_LITE5200 || PPC_83xx || \
>> -		   (PPC_85xx && !PPC_E500MC) || PPC_86xx || PPC_PSERIES \
>> -		   || 44x || 40x
>> +	def_bool n
>>  
>>  config ARCH_SUSPEND_NONZERO_CPU
>>  	def_bool y
>> @@ -568,8 +566,7 @@ config ARCH_USING_PATCHABLE_FUNCTION_ENTRY
>>  
>>  config HOTPLUG_CPU
>>  	bool "Support for enabling/disabling CPUs"
>> -	depends on SMP && (PPC_PSERIES || \
>> -		PPC_PMAC || PPC_POWERNV || FSL_SOC_BOOKE)
>> +	depends on SMP && (ARCH_HIBERNATION_POSSIBLE || ARCH_SUSPEND_POSSIBLE)
>>  	help
>>  	  Say Y here to be able to disable and re-enable individual
>>  	  CPUs at runtime on SMP machines.