Re: [RFC PATCH 02/12] powerpc: remove arguments from interrupt handler functions

[Nicholas Piggin <npiggin@gmail.com>]

Excerpts from Christophe Leroy's message of September 7, 2020 7:20 pm:
> 
> 
> Le 05/09/2020 à 19:43, Nicholas Piggin a écrit :
>> Make interrupt handlers all just take the pt_regs * argument and load
>> DAR/DSISR etc from that. Make those that return a value return long.
> 
> I like this, it will likely simplify a bit the VMAP_STACK mess.
> 
> Not sure it is that easy. My board is stuck after the start of init.
> 
> 
> On the 8xx, on Instruction TLB Error exception, we do
> 
> 	andis.	r5,r9,DSISR_SRR1_MATCH_32S@h /* Filter relevant SRR1 bits */
> 
> On book3s/32, on ISI exception we do:
> 	andis.	r5,r9,DSISR_SRR1_MATCH_32S@h /* Filter relevant SRR1 bits */
> 
> On 40x and bookE, on ISI exception we do:
> 	li	r5,0			/* Pass zero as arg3 */
> 
> 
> And regs->dsisr will just contain nothing
> 
> So it means we should at least write back r5 into regs->dsisr from there 
> ? The performance impact should be minimal as we already write _DAR so 
> the cache line should already be in the cache.

Yes, I think that would be required. Sorry I didn't look closely at
32 bit.

> A hacky 'stw r5, _DSISR(r1)' in handle_page_fault() does the trick, 
> allthough we don't want to do it for both ISI and DSI at the end, so 
> you'll have to do it in every head_xxx.S
> 
> 
> While you are at it, it would probably also make sense to do remove the 
> address param of bad_page_fault(), there is no point in loading back 
> regs->dar in handle_page_fault() and machine_check_8xx() and 
> alignment_exception(), just read regs->dar in bad_page_fault()
> 
> The case of do_break() should also be looked at.

Yeah that's valid, I didn't do that because bad_page_fault was also
being called from asm, but an incremental patch should be quite easy.

> Why changing return code from int to long ?

Oh it's to make the next patch work without any changes to function
prototypes. Some handlers are returning int, others long. There is
no reason not to just return long AFAIKS so that's what I changed to.

Thanks,
Nick