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

On Tue, 2016-06-28 at 14:01 +0200, Benjamin Herrenschmidt wrote:

On Tue, 2016-06-28 at 13:42 +0200, Gerhard Pircher wrote:

quoted

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).

quoted

quoted

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