[PATCH] drm/nouveau/mmu/nv4a: use nv04 mmu rather than the nv44 one

[Ilia Mirkin]

On Sun, Mar 26, 2017 at 6:14 PM, Ben Skeggs <skeggsb at gmail.com> wrote:
> On 03/19/2017 06:23 AM, Ilia Mirkin wrote:
>>
>> The NV4A (aka NV44A) is an oddity in the family. It only comes in AGP
>> and PCI varieties, rather than a core PCIE chip with a bridge for
>> AGP/PCI as necessary. As a result, it appears that the MMU is also
>> non-functional. For AGP cards, the vast majority of the NV4A lineup,
>> this worked out since we force AGP cards to use the nv04 mmu. However
>> for PCI variants, this did not work.
>>
>> Switching to the NV04 MMU makes it work like a charm. Thanks to mwk for
>> the suggestion. This should be a no-op for NV4A AGP boards, as they were
>> using it already.
>
> This is probably fine for NV4A in that case (more below).
>
>>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=70388
>> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
>> Cc: stable at vger.kernel.org
>> ---
>>
>> OK, so I'm not 100% sure about my claims, but I don't have the necessary
>> hardware to test it out. Right now, AGP nv41+ boards are getting the nv04
>> mmu, while PCI nv41+ boards are getting the PCIE one. Perhaps this works
>> for them, however such boards are rare, and I don't have one. Perhaps all
>> PCI boards should be routed to the nv04 mmu, not just the NV4A ones.
>
> I wonder if it wouldn't be useful to also change the checks in nv41/nv44
> implementations to be "if (device->type != NVKM_DEVICE_PCIE ..." too?

So ... mwk and I were talking about it, and we weren't sure. Were
there non-NV4A, non-IGP PCI boards? And if so, if it's a PCIE <-> PCI
thing that translates the bus transactions, the GPU-side MMU should
still be there, no? (Is there anything PCIE-specific going on?) In
case you can't tell, I'm well past the edge of my understanding of how
all this works...

Perhaps you could check if you have such a board, or if they're purely
mythical? If such boards do exist, see what happens when you plug it
in and boot nouveau with it. My issues with NV4A were immediate - the
fifo basically didn't initialize. If the boards are mythical, then we
can just change nv44/nv41 to check for != PCIE.

Cheers,

  -ilia