[Nouveau] [PATCH v4] pmu/gk20a: PMU boot support

[Ben Skeggs]

On 12 May 2015 at 19:04, Alexandre Courbot <gnurou at gmail.com> wrote:
> Hi Ben,
>
> On Fri, May 1, 2015 at 8:01 AM, Ben Skeggs <skeggsb at gmail.com> wrote:
>> On 13 April 2015 at 20:42, Alexandre Courbot <acourbot at nvidia.com> wrote:
>>> Ben, I guess our main remaining concern with this patch is how it should
>>> integrate wrt. the existing PMU code. Since it is designed to interact with
>>> the NVIDIA firmware, maybe we should use a different base code, or do you
>>> think we can somehow share code and data structures?
>> Hey Alexandre,
>>
>> Sorry for the delay in responding to this.
>
> It is my turn to apologize - I was (well still am, technically :)) on
> holidays and have just started unpiling my inbox...
>
>>
>> My original thinking with transitioning to use NVIDIA's firmware was
>> that I'd modify our firmware interfaces to match yours, and share the
>> code.  I haven't started on any of this yet due to not having any word
>> on how you guys will be shipping the images, etc.  It would be nice to
>> have some communication on these things :)
>
> Indeed. For the first time with Maxwell GPUs, NVIDIA-provided firmware
> will be required for GPUs to operate properly. This raises several
> questions:
>
> - Should the firmware be released under /lib/firmware/nouveau or
> /lib/firmware/nvidia ? (this directory already exists for Tegra USB
> firmware and makes more sense to me, since the firmware is not
> Nouveau-specific)
I think /lib/firmware/nvidia makes sense here too.

> - For GPCCS/FECS firmware, should we release the netlist "pack" file
> or adopt the same format as Nouveau does? (1 file per firmware)
> - Should we keep the current files names (e.g. nvxx_fucxxxx[cd]), or
> try to switch to more meaningful ones?
I'd actually prefer to have the entire netlists bundled, that gives us
updated reg/ctx production values too as you guys tweak/update them
for hw bugs (etc).  They're also nicer in that you get a single bundle
of everything that's required for that chipset+engine.

I don't have too much opinion on naming.  The current model of
nv{CHIPSET}_{UCODE_TYPE}{REGISTER_BASE}[CODE,DATA] was just nice and
convenient to snprintf into a buffer :)

> - What about signature files that are required for secure boot?
As with above, if it's possible to ship them in a single file with the
ucode that it belongs to, that'd be ideal.  It's not a huge deal
though.

> - Knowing that NVIDIA's firmware ABI is a (very slowly) moving target,
> it is worth to aim at ABI compatibility, or should we assume different
> paths for Nouveau and NVIDIA firmware? If ABI incompatibilities are
> introduced in the way, how do we handle versioning?
For incompatible changes, I think appending a -VERSION to each
firmware blob is probably the simplest approach.  The driver can
select the necessary codepath based on what it finds (probably trying
newer versions first, obviously).

>
> All these issues make me tend towards having a separate handling of
> NVIDIA-released firmware (location, format, and ABI). It will also
> make the firmware easier to release if conversions are not necessary
> on the way out. What are your thoughts on this?
I'm not entirely set here, either way.  I somewhat think that
initially I should adapt our interfaces to match, and a keep single
code path as long as we can.  A lot of the changes so far have seemed
minor enough we could stick conditionals on firmware version, and if
fw changes come along that warrant a radical change in handling from
the host, we can abstract it away then.

But, I'm open to other suggestions :)

Ben.

>
>> I'm suspecting you won't be wanting to modify our falcon assembly, so
>> I guess I'll set aside some time to use this patch as a base and
>> transition our ucode to boot using it?  Then you guys can build more
>> stuff on top of that.  I'm also happy to let you modify our ucode if
>> you wish :)
>
> There may be legal issues with us touching the Nouveau firmware. But
> as I stated above, the first question is do we want to bother with
> this compatiblity at all?