[PATCH v2] powerpc xmon: use `dcbf` inplace of `dcbi` instruction for 64bit Book3S

[Christophe Leroy]

Le 26/03/2020 à 07:15, Balamuruhan S a écrit :
> Data Cache Block Invalidate (dcbi) instruction was implemented back in PowerPC
> architecture version 2.03. It is obsolete and attempt to use of this illegal
> instruction results in a hypervisor emulation assistance interrupt. So, ifdef
> it out the option `i` in xmon for 64bit Book3S.

I don't understand. You say two contradictory things:
1/ You say it _was_ added back.
2/ You say it _is_ obsolete.

How can it be obsolete if it was added back ?

[...]

> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 0ec9640335bb..bfd5a97689cd 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -335,10 +335,12 @@ static inline void cflush(void *p)
>   	asm volatile ("dcbf 0,%0; icbi 0,%0" : : "r" (p));
>   }
>   
> +#ifndef CONFIG_PPC_BOOK3S_64

You don't need that #ifndef. Keeping it should be harmless.

>   static inline void cinval(void *p)
>   {
>   	asm volatile ("dcbi 0,%0; icbi 0,%0" : : "r" (p));
>   }
> +#endif
>   
>   /**
>    * write_ciabr() - write the CIABR SPR
> @@ -1791,8 +1793,9 @@ static void prregs(struct pt_regs *fp)
>   
>   static void cacheflush(void)
>   {
> -	int cmd;
>   	unsigned long nflush;
> +#ifndef CONFIG_PPC_BOOK3S_64

Don't make it so complex, see below

> +	int cmd;
>   
>   	cmd = inchar();
>   	if (cmd != 'i')
> @@ -1800,13 +1803,14 @@ static void cacheflush(void)
>   	scanhex((void *)&adrs);
>   	if (termch != '\n')
>   		termch = 0;
> +#endif
>   	nflush = 1;
>   	scanhex(&nflush);
>   	nflush = (nflush + L1_CACHE_BYTES - 1) / L1_CACHE_BYTES;
>   	if (setjmp(bus_error_jmp) == 0) {
>   		catch_memory_errors = 1;
>   		sync();
> -
> +#ifndef CONFIG_PPC_BOOK3S_64

You don't need that ifndef, just ensure below that regardless of cmd, 
book3s/64 calls cflush and not cinval.

>   		if (cmd != 'i') {

The only thing you have to do is to replace the above test by:

		if (cmd != 'i' || IS_ENABLED(CONFIG_PPC_BOOK3S_64)) {

>   			for (; nflush > 0; --nflush, adrs += L1_CACHE_BYTES)
>   				cflush((void *) adrs);
> @@ -1814,6 +1818,10 @@ static void cacheflush(void)
>   			for (; nflush > 0; --nflush, adrs += L1_CACHE_BYTES)
>   				cinval((void *) adrs);
>   		}
> +#else

Don't need that at all, it's a duplication of the above.

> +		for (; nflush > 0; --nflush, adrs += L1_CACHE_BYTES)
> +			cflush((void *)adrs);
> +#endif
>   		sync();
>   		/* wait a little while to see if we get a machine check */
>   		__delay(200);
> 
> base-commit: a87b93bdf800a4d7a42d95683624a4516e516b4f
> 

Christophe