Sequoia kernel crash workaround.

[Valentine Barshak]

Josh Boyer wrote:
> On Thu, 20 Sep 2007 12:32:56 -0500 (CDT)
> Milton Miller <miltonm at bga.com> wrote:
> 
>> On Fri Sep 21 02:56:32 EST 2007, Valentine Barshak wrote:
>>> Josh Boyer wrote:
>>>> On Wed, 19 Sep 2007 14:30:24 -0500
>>>> Olof Johansson <olof at lixom.net> wrote:
>>>>
>>>>> On Wed, Sep 19, 2007 at 09:19:47PM +0200, Stefan Roese wrote:
>>>>>> Hi Valentine,
>>>>>>
>>>>>> On Wednesday 19 September 2007, Valentine Barshak wrote:
>>>>>>> Disabling write pipelining really helps.
>>>>>>> Josh, David, what is the right place to put this workaround to?
>>>>>>>
>>>>>>> Is it OK to do mtdcr(PLB4A0_ACR, mfdcr(PLB4A0_ACR) & ~PLB4_WRP); in
>>>>>>> arch/powerpc/boot/cuboot-sequoia.c:sequoia_fixups()?
>>>>>>> or
>>>>>>> should this be done in
>>>>>>> arch/powerpc/platforms/44x/sequoia.c:sequoia_setup_arch()
>>>>>>> with dcr_map, dcr_read/write stuff?
>>>>>> I vote for putting it into sequoia.c, since it's very likely to happen that 
>>>>>> Sequoia will at one point be booted without the bootwrapper. Or perhaps it 
>>>>>> should go into some common code checking the PVR and disabling it when this 
>>>>>> 440EPx/GRx is detected, since all those boards are affected.
>>>>> This is what we have setup_cpu functions in the cpu table for. Please
>>>>> put it there instead of in board code.
>>>> Yes, agreed.
>>> I was thinking about it. Looks like it's the best place, but the code 
>>> that actually calls setup_cpu is under ifdef CONFIG_PPC64, while lots of 
>>> cpu_setup functions are defined for ppc32 processors.
>>> Is it OK to remove this ifdef, or should I do CONFIG_PPC64 || CONFIG_44x?
>> head_32.S calls call_setup_cpu in misc_32.S to call the cpu setup functon.
>>
>> Note that these functions are called before the kernel is copied down to
>> 0, so on ppc32 you will need the PTRRELOC type stuff.  Also the callsite
>> implies that the cpu number is available in r24, which may or may not be
>> true when called from C.
>>
>> Its probably easier to just call call_setup_cpu in the other 32 bit 
>> head_xxx files.
> 
> Hm.  I'll have to see how well that would work for 4xx.  Seems 8xx and
> FSL BookE are in a similar situation.

I started preparing the patch after Olof's "take out the ifdef" :)
I've tested it on 4xx. seems to work fine. FPU works OK and EPX/GRX 
workaround is fine also, but it has to be tested on 8xx and fsl.
Adding call_setup_cpu to head_44x is no problem.

> 
> josh