[PATCH 29/38] powerpc: Move 32-bit probe() machine to later in the boot process

[Gerhard Pircher]

On Tue, 2016-06-28 at 14:01 +0200, Benjamin Herrenschmidt wrote:
> On Tue, 2016-06-28 at 13:42 +0200, Gerhard Pircher wrote:
> > The question is, if a compile time option that simply clear ?s
> > CPU_FTR_NEED_COHERENT after identify_cpu() would be acceptable. And
> > then I still wonder why KVM needs its own similar fix to work on the
> > AmigaOne. I specifically had to remove/clear the PTE_M bit
> > inarch/powerpc/kvm/book3s_32_mmu_host.c for th
> 
> No we could just add something to early_init_devtree that does clear
> that bit if it sees the relevant piece of broken HW, it's not the AmigaOne per-se, it's the northbridge right ?
Does that work for CPU_FTR_NEED_COHERENT, given that the feature fixups
are done right after identify_cpu() and instructions within BEGIN_FTR_SECTION
and END_FTR_SECTION* are patched out (if I understand this mechanism
correctly) !?
But yes, the specific northbridge is the problem here.

> We could also make non-coherent cache a runtime option if we really
> wanted, it's just more churn ...
Yeah, I remember a discussion or two about this topic and I always wondered
how driver code would differentiate then between non-coherent and coherent
DMA, given that they sometimes require different handling of the DMA addresses
(e.g. if I look at /sound/core/pcm_native.c or the DRM code).

> > > Do we know where the lockups come from btw ? A problem with the
> > > northbridge ?
> > Yes, it's a problem with the northbridge...as usual. :-(
> 
> Marvell ?
No, the one with the dreaded "A" name: MAI Logic's "Articia S" :-)

BR,
Gerhard