Re: [PATCH v1 02/19] powerpc/64e: Tie PPC_BOOK3E_64 to PPC_E500MC

[Christophe Leroy]

Le 09/09/2022 à 07:50, Michael Ellerman a écrit :
> Hi Christophe,
> 
> Thanks for trying to clean up this tangled mess.
> 
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
>> The only 64-bit Book3E CPUs we support is the e500mc.
> 
> AFAIK the e500mc is 32-bit?

Yes it seems.

> 
> We support e5500 and e6500 which are 64-bit Book3E.
> 
> They're derivatives of the e500mc AIUI.
> 
> So CONFIG_PPC_E500MC actually means e500mc *and later derivatives*.
> 
> You can see that with eg:
> 
> config SPE_POSSIBLE
> 	def_bool y
> 	depends on E500 && !PPC_E500MC
> 
> Because e500mc dropped SPE, and so therefore e5500 and e6500 don't have
> it either.
> 
> And eg:
> 
> #ifdef CONFIG_PPC_E500MC
> _GLOBAL(__setup_cpu_e6500)
> 	mflr	r6
> 
> 
>> However our Kconfig allows configurating a kernel that has 64-bit
>> Book3E support, but no e500mc support enabled. Such a kernel
>> would never boot, it doesn't know about any CPUs.
> 
> That is true.
> 
>> To fix this, force e500mc to be selected whenever we are
>> building a 64-bit Book3E kernel.
> 
> I think that's a reasonable fix, just it's important to differentiate
> between CONFIG_PPC_E500MC (the symbol) and e500mc (the CPU).

Ok, I'll see how I can make it more explicit.

> 
>> And add a test to detect futur situations where cpu_specs is empty.
>                             future
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
>> ---
>>   arch/powerpc/kernel/cputable.c         | 2 ++
>>   arch/powerpc/platforms/Kconfig.cputype | 2 ++
>>   2 files changed, 4 insertions(+)
>>
> ..
>> diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
>> index 5185d942b455..19fd95a06352 100644
>> --- a/arch/powerpc/platforms/Kconfig.cputype
>> +++ b/arch/powerpc/platforms/Kconfig.cputype
>> @@ -108,6 +108,8 @@ config PPC_BOOK3S_64
>>   config PPC_BOOK3E_64
>>   	bool "Embedded processors"
>>   	select PPC_FSL_BOOK3E
>> +	select E500
>> +	select PPC_E500MC
>>   	select PPC_FPU # Make it a choice ?
>>   	select PPC_SMP_MUXED_IPI
>>   	select PPC_DOORBELL
> 
> I think that makes the select of PPC_E500MC below redundant:
> 
> config PPC_QEMU_E500
> 	bool "QEMU generic e500 platform"
> 	select DEFAULT_UIMAGE
> 	select E500
> 	select PPC_E500MC if PPC64

That's handled in  [v1,10/19] powerpc: Remove redundant selection of 
E500 and E500MC. Should I reorder patches ?

Thanks
Christophe