[Nouveau] [RESEND PATCH nouveau 3/3] volt: add support for GK20A

[Terje Bergström]

On 29.11.2014 10:44, Alexandre Courbot wrote:
> On Fri, Nov 28, 2014 at 9:09 PM, Roy Spliet <seven at nimrod-online.com> wrote:
>> I'm not sure if I completely understand your reply, so forgive me if I am
>> stating some obvious things:
>> The reason why I brought this up is because, the way I see it, DTS is the
>> replacement for (V)BIOS on ARM platforms, giving a set of parameters that
>> drivers (nouveau) can use for that particular instance (the Tegra K1 SoC) of
>> some more generic IP (gk20a). All the other devices nouveau supports have a
>> VBIOS to describe this kind of information to us, hence we haven't seen this
>> before. For CPUs there are plenty of examples though of such params defined
>> in DT: in arch/arm/boot/dts/ : imx6qdl.dtsi documents the min and max volt
>> for regulators, while the CPUs have a little freq<->volt mapping in
>> imx6q.dtsi. GPUs are new in a sense that NVIDIA is the first to actively
>> support upstream development (thanks!)
> Thanks for raising this point. I agree with your interpretation that
> DT is comparable to the VBIOS in desktop GPUs. The question then
> becomes whether this data can vary between different GK20A-using
> boards (and in this case this should probably be part of DT) or not
> (in which case I would advocate having this static information in the
> driver itself). Since I don't expect different GK20A-using chips to
> require different voltage for given frequencies, my gut feeling for
> the moment is that having this information in the driver is fine. I
> have added a few other NVIDIA people to gather thoughts.

The voltage<->frequency relationship is per chip, not per board. We read
the chip id at runtime, and programmatically determine the DVFS steps
based on that. CVB table contains the parameters for the algorithm.

I think the table belongs in the driver. The table is not per board, and
the values in CVB table do not describe hardware, but parameters to an
algorithm.

Terje

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