[OpenBIOS] [PATCH v3] ppc: use rfid when running under a CPU from the 970 family.

[Alexander Graf]

> Am 22.06.2016 um 09:29 schrieb Cédric Le Goater <clg at kaod.org>:
> 
> A recent attempt to restrict the use of rfi on 64bit cpus in qemu
> broke 32bit OpenBIOS when run under a 970.
> 
> This patches memory to replace rfi instructions with rfid in the
> vector code.
> 
> Signed-off-by: Cédric Le Goater <clg at kaod.org>
> Suggested-by: Alexander Graf <agraf at suse.de>
> ---
> 
> Tested on qemu.
> 
> Changes since v2 :
> 
> - make it nicer
> 
> arch/ppc/qemu/ofmem.c |   26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
> 
> Index: openbios.git/arch/ppc/qemu/ofmem.c
> ===================================================================
> --- openbios.git.orig/arch/ppc/qemu/ofmem.c
> +++ openbios.git/arch/ppc/qemu/ofmem.c
> @@ -478,6 +478,30 @@ isi_exception(void)
>     hash_page(nip, phys, mode);
> }
> 
> +/* When running on ppc64, we cannot use rfi anymore. Let's patch the
> + * vectors to use rfid instead.

Please use

/*
 * Comments like this
 */

and explain exactly why "we can not use rfi anymore", so that someone looking at the code in 5 years will still know what's going on.

> + */
> +#define RFI     0x4c000064
> +#define RFID    0x4c000024
> +
> +extern char __vectors[];
> +extern char __vectors_end[];
> +
> +static void patch_rfi(void)
> +{
> +    uint32_t* ptr;
> +    uint32_t* vec_start = (uint32_t*) 0x100UL;
> +    uint32_t* vec_end = (uint32_t*) (__vectors_end - __vectors);
> +
> +    if (!is_ppc64())
> +        return;
> +
> +    for (ptr = vec_start; ptr < vec_end; ptr++)  {

Last time I asked < was not really defined for pointers. You can only match (==, !=) or convert to numbers (uintptr_t) them. The smaller comparison might work for now, but I can't guarantee it won't break in gcc7 or so.

In short, please just make it != :).

Alex

> +        if (*ptr == RFI)
> +            *ptr = RFID;
> +    }
> +    flush_icache_range((char*) vec_start , (char*) vec_end);
> +}
> 
> /************************************************************************/
> /*    init / cleanup                            */
> @@ -532,6 +556,8 @@ setup_mmu(unsigned long ramsize)
> 
>     memcpy((void *)get_rom_base(), (void *)OF_CODE_START, OF_CODE_SIZE);
> 
> +    patch_rfi();
> +
>     /* Enable MMU */
> 
>     mtmsr(mfmsr() | MSR_IR | MSR_DR);