Re: [PATCH v3] parisc: Fix crash due alternative coding for NP iopdir_fdc bit

[Sven Schnelle <svens@stackframe.org>]

Hi,

On Thu, May 30, 2019 at 09:55:43PM +0200, Sven Schnelle wrote:
> Hi,
> 
> On Wed, May 29, 2019 at 04:15:03PM +0200, Helge Deller wrote:
> > >> Exactly. And as:
> > >>
> > >> a) All C3600 PDC versions clear the NP bit
> > >> b) All C37XX/J5000 PDC version set the NP bit
> > >>
> > >> i don't think there's some bug in the PDC. I would guess that the patch Carlo
> > >> reported to fix issues is just hiding the real problem. Would be interesting
> > >> to run Carlo's Test on a C37XX.
> > >
> > > Probably, hardware cache coherent I/O is not implemented correctly for Elroy based systems.
> > > https://www.hpl.hp.com/hpjournal/96feb/feb96a6.pdf
> > > Does it work on C360?
> > 
> > I slowly start to get confused...
> > Just thinking about another possibility: Maybe we can rely on the value of the
> > NP iopdir_fdc bit only on machines with >= PA8700 CPUs?
> > For older machines (which would need opdir_fdc) HP-UX or other operating
> > systems decides on the found CPU.
> > This would explain why it's not  set on Carlo's C3600, and if Sven's C240
> > (with a PA8200 CPU) doesn't has the bit set too, then this could explain this theory.
> 
> I just re-tested my kexec branch, and the HPMC i was seeing when kexec'ing a new
> kernel on my J5000 is now gone with Helge's patch. J5000 also has PCX-W. It was
> only triggered when i had SMP enabled, but this is somehow not suprising given
> the fact that a cache flush was missing.

Looks like i'm also confused now. My J5000 crashed with the kexec stuff again.
It's much less than before, only 1 out of 10 times.

The patch does:

                if ((cond & ALT_COND_NO_IOC_FDC) &&
                       ((boot_cpu_data.cpu_type < pcxw) ||
                        (boot_cpu_data.cpu_type == pcxw_) ||
                        (boot_cpu_data.pdc.capabilities & PDC_MODEL_IOPDIR_FDC)))
                        continue;

So there should be no change for PCX-W and my statement that this fixes anything
on my J5000 is wrong. I think i'll disable the patching and see whether the problem
disappears.

Regards
Sven