[Skiboot] [PATCH 07/16] core: hardcode P9 large decrementer width

[Nicholas Piggin]

Stewart Smith's on February 13, 2019 1:38 pm:
> Michael Neuling <mikey at neuling.org> writes:
>> On Tue, 2019-02-12 at 12:23 +1100, Stewart Smith wrote:
>>> Oliver <oohall at gmail.com> writes:
>>> > On Mon, Feb 11, 2019 at 3:12 PM Stewart Smith <stewart at linux.ibm.com> wrote:
>>> > > Nicholas Piggin <npiggin at gmail.com> writes:
>>> > > > There is no good reason to "discover" the large decremeter width.
>>> > > > We are firmware, we know the large decrementer width.
>>> > > > 
>>> > > > Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
>>> > > 
>>> > > Oliver - do you remember the original motivation around detecting it
>>> > > rather than just coding how many bits there were? Was it because we were
>>> > > experimenting with things in sim before the HW design was finalised? Or
>>> > > are we just being fancy?
>>> > 
>>> > Dunno. I'm pretty sure this was one of the first bits of skiboot code
>>> > I wrote so either,
>>> > 
>>> > a) I was overthinking it, or
>>> > b) Mikey told me to.
>>> > 
>>> > I do remember having to get some mambo bugs fixed to test it though.
>>> > So it's possible the actual size wasn't finalised yet.
>>> 
>>> Mikey, was it (b) ?
>>> 
>>> (and at this point am *I* overthinking this? Hard-coding it is *fine*)
>>
>> IIRC, we wanted to make it future proof and it was easy enough to do, so we did.
>>
>> Is there a problem with auto detecting it?
> 
> Not really? I'll drop this patch for the time being.

Ah, I ran into a problem when running a later patch that set a
decrementer timer ticking during boot, bad things happened here,
fixed with this patch.

That's not a serious patch yet, so this can wait.

I'm generally in favour of hard coding things when we know
them, but presumably this could also be fixed by disabling
EE over the detection if people want to keep the detection.

Thanks,
Nick