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

[Cédric Le Goater]

On 06/22/2016 09:41 AM, Alexander Graf wrote:
> 
> 
>> 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.

yep.

>> + */
>> +#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.

oh yes. that is true.

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

Thanks,

C.
 
> 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);
>