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

[Alexander Graf]

On 06/20/2016 02:59 PM, Cédric Le Goater wrote:
> On 06/20/2016 11:49 AM, Mark Cave-Ayland wrote:
>> On 20/06/16 10:33, Alexander Graf wrote:
>>
>>> On 06/20/2016 11:32 AM, Cédric Le Goater wrote:
>>>> On 06/20/2016 09:39 AM, Alexander Graf wrote:
>>>>> On 20.06.16 09:34, Cédric Le Goater wrote:
>>>>>> A recent attempt to restrict the use of rfi to 64bit cpus in qemu
>>>>>> broke 32bit OpenBIOS when run under a 970.
>>>>>>
>>>>>> This is adding a dynamic check on the pvr to choose between rfi and
>>>>>> rfid. Only the 970 family is supported.
>>>>>>
>>>>>> Signed-off-by: Cédric Le Goater <clg at kaod.org>
>>>>>> ---
>>>>>>
>>>>>>    Tested on qemu.
>>>>>>
>>>>>>    arch/ppc/qemu/start.S |   25 +++++++++++++++++++++++--
>>>>>>    arch/ppc/start.S      |   25 +++++++++++++++++++++++--
>>>>>>    2 files changed, 46 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> Index: openbios.git/arch/ppc/qemu/start.S
>>>>>> ===================================================================
>>>>>> --- openbios.git.orig/arch/ppc/qemu/start.S
>>>>>> +++ openbios.git/arch/ppc/qemu/start.S
>>>>>> @@ -27,6 +27,27 @@
>>>>>>      #ifdef CONFIG_PPC_64BITSUPPORT
>>>>>>    +/* When running on ppc64, we cannot use rfi anymore. Let's try to
>>>>>> + * catch which cpu we are running on and act accordingly. This is
>>>>>> + * for 970s only.
>>>>> Do you think you could move the check into the cpu init function and use
>>>>> a global variable / live patching instead? I don't remember if we need
>>>>> to handle any faults before we reach that path.
>>>> So we get an ISI really early, when returning from setup_mmu(), which is
>>>> the first call in _entry.
>>> Ok, can we add the check there?
>> Bear in mind that the code for entry/context switching has been reworked
>> pending commit whilst we switch the OpenBIOS repository over from SVN to
>> git. The relevant commits are here:
>> https://www.coreboot.org/pipermail/openbios/2016-May/009395.html.
>>
>> So please consider OpenBIOS git master plus the patchset above to be the
>> latest code.
> OK. The first version applies fine. I pushed everything here :
>
> 	https://github.com/legoater/openbios/commits/master
>
> I am still looking at what Alex is asking for : a global variable doing
> live patching for rfi.

It's not both - it's either or :).

So either you define a global variable that we can just read from to 
determine whether we do rfi or rfid or we live patch. Looking at the 
code, it's probably easiest to live patch even. Just call a function 
from setup_mmu() that checks PVR and if it's 64bit, loops through (0x0 
.. 0x1000) in 32bit steps and checks if *p == INST_RFI. If so, replace 
with INST_RFID and flush the cache.


Alex