Re: [PATCH][RFC] parisc: Use local tlb purges only on PA2.0 machines

[John David Anglin <dave.anglin@bell.net>]

On 2022-09-25 4:11 p.m., Helge Deller wrote:
> n 9/25/22 22:02, John David Anglin wrote:
>> On 2022-09-25 2:57 p.m., Helge Deller wrote:
>>> +#ifdef CONFIG_PA20
>>> +#define ALT_COND_PACACHE    ALT_COND_ALWAYS
>>> +#else
>>> +#define ALT_COND_PACACHE    ALT_COND_NO_SMP
>>> +#endif
>>> +
>>>   ENTRY_CFI(flush_tlb_all_local)
>>>       /*
>>>        * The pitlbe and pdtlbe instructions should only be used to
>>> @@ -539,15 +545,10 @@ ENTRY_CFI(copy_user_page_asm)
>>>
>>>       /* Purge any old translations */
>>>
>>> -#ifdef CONFIG_PA20
>>> -    pdtlb,l        %r0(%r28)
>>> -    pdtlb,l        %r0(%r29)
>>> -#else
>>>   0:    pdtlb        %r0(%r28)
>>>   1:    pdtlb        %r0(%r29)
>>> -    ALTERNATIVE(0b, 0b+4, ALT_COND_NO_SMP, INSN_PxTLB)
>>> -    ALTERNATIVE(1b, 1b+4, ALT_COND_NO_SMP, INSN_PxTLB)
>>> -#endif
>>> +    ALTERNATIVE(0b, 0b+4, ALT_COND_PACACHE, INSN_PxTLB)
>>> +    ALTERNATIVE(1b, 1b+4, ALT_COND_PACACHE, INSN_PxTLB)
>> This doesn't look correct.  If ALT_COND_PACACHE is defined as ALT_COND_NO_SMP, the pdtlb
>> instructions will be converted to pdtlb,l instructions when running UP.  These are not supported
>> on PA 1.1. 
>
> Your concern is correct, but there is an additonal check in the alternative-coding,
> which prevents enabling the local flag if we're not running on a PA2.0 CPU.
> So, those ALTERNATIVE() macros will only apply on PA2.0 machines.
You are correct.  Missed that.

That only leaves the bus serialization issue when pdtlb is used on an SMP machine.

Dave


-- 
John David Anglin  dave.anglin@bell.net