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Subject: Re: [RFC PATCH 02/12] powerpc: remove arguments from interrupt
 handler functions
To: Nicholas Piggin <npiggin@gmail.com>
References: <20200905174335.3161229-1-npiggin@gmail.com>
 <20200905174335.3161229-3-npiggin@gmail.com>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
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Date: Mon, 7 Sep 2020 11:20:10 +0200
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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.

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.

Why changing return code from int to long ?

Christophe

> 
> This is done to make the function signatures match more closely, which
> will help with a future patch to add wrappers. Explicit arguments could
> be re-added for performance in future but that would require more
> complex wrapper macros.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>   arch/powerpc/include/asm/asm-prototypes.h |  4 ++--
>   arch/powerpc/include/asm/bug.h            |  4 ++--
>   arch/powerpc/kernel/exceptions-64e.S      |  2 --
>   arch/powerpc/kernel/exceptions-64s.S      | 14 ++------------
>   arch/powerpc/mm/book3s64/hash_utils.c     |  8 +++++---
>   arch/powerpc/mm/book3s64/slb.c            | 11 +++++++----
>   arch/powerpc/mm/fault.c                   | 16 +++++++++-------
>   7 files changed, 27 insertions(+), 32 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index d714d83bbc7c..2fa0cf6c6011 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/arch/powerpc/include/asm/bug.h
> @@ -111,8 +111,8 @@
>   #ifndef __ASSEMBLY__
>   
>   struct pt_regs;
> -extern int do_page_fault(struct pt_regs *, unsigned long, unsigned long);
> -extern int hash__do_page_fault(struct pt_regs *, unsigned long, unsigned long);
> +extern long do_page_fault(struct pt_regs *);
> +extern long hash__do_page_fault(struct pt_regs *);

no extern

>   extern void bad_page_fault(struct pt_regs *, unsigned long, int);
>   extern void _exception(int, struct pt_regs *, int, unsigned long);
>   extern void _exception_pkey(struct pt_regs *, unsigned long, int);

Christophe