[Nouveau] Second copy engine on GF116

[Ilia Mirkin]

On Fri, Nov 21, 2014 at 1:16 AM, Andy Ritger <aritger at nvidia.com> wrote:
> Hi Ilia,
>
> Actually 0x90b8 is different than copy engine.  I'm not very familiar
> with it, but 0x90b8 is an engine for performing LZO decompression as
> part of performing the copy.  It has a variety of limitations (e.g.,
> cannot handle blocklinear format), and was only in a few Fermi chips,
> as I understand it.

According to our driver source, GF100, GF104, GF110, GF114, and GF116
all have it. [So GF106, GF108, GF117, GF119 don't have it.] We've only
had problems reported against GF116... and only for some people.

>
> It is probably easiest to just ignore it.  You can distinguish this
> decompress engine from normal copy engine by looking at the CE capability
> register on falcon (0x00000650).  If bit 2 is '1', then the falcon is
> a decompress engine.

I presume you mean a +0x650 register on the pcopy engines (0x104000
and 0x105000). I only have access to the GF108 right now, which
returns 3 for 0x104650 and 4 for 0x105650. We're using the engine at
0x104000 for copy on the GF108...

>From my admittedly limited understanding, both 0x104000 and 0x105000
appear to be falcon engines, where the fuc is presumably able to drive
some underlying hardware. The actual fifo methods are implemented in
the fuc, which in turn does iowr/etc commands.

Are you saying that the "decompress" engine (at 0x105000 right?) has a
different piece of hardware behind it than the copy engine at
0x104000, or does NVIDIA simply provide different fuc for it that
exposes somewhat different functionality via FIFO methods?

>
> I hope that helps,
> - Andy
>
>
> On Thu, Nov 20, 2014 at 02:18:02PM -0500, Ilia Mirkin wrote:
>> Hello,
>>
>> There's a long-standing bug on nouveau (this is a sample bug, but the
>> issue has been around for a while:
>> https://bugs.freedesktop.org/show_bug.cgi?id=85465) whereby we attempt
>> to use the second PCOPY engine on GF116, and it is sometimes does
>> nothing, despite mmio register 22500 saying that it's not disabled
>> (0x22500 == 0 for this user). In the bug you can see a dump from
>> 22400..22600, and all values after 22440 are read as 0. The issue
>> appears to be more common on mobile GF116's, but I don't know that the
>> correlation is 100%. No errors are reported by the FIFO or invalid
>> mmio reads, but the data transfer just does not happen. Switching to
>> using the first copy engine resolves things, so it's unlikely to be a
>> more systemic issue in nouveau's usage of the copy engine.
>>
>> To be clear, when I'm talking about the second PCOPY engine, I'm
>> talking about the engine at mmio 0x105000, and whose fifo class id is
>> 0x90b8.
>>
>> Any information on properly detecting that the engine is, in fact,
>> missing, would be greatly appreciated. Or, conversely, an assurance
>> that the engine _is_ there on all GF116's and we're just not
>> initializing something properly, along with perhaps some suggestions
>> as to what we might be missing.
>>
>> Thanks,
>>
>> Ilia Mirkin
>> imirkin at alum.mit.edu
>> _______________________________________________
>> Nouveau mailing list
>> Nouveau at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/nouveau