[Nouveau] PWM-based voltage management input clock

[Andy Ritger]

Thanks, Martin.  I'll try to follow up on this next week and get you an answer.  What GPUs have you observed this on?


On Fri, Sep 18, 2015 at 11:13:53PM +0300, Martin Peres wrote:
> Hello,
> 
> We recently reverse engineered PWM-based voltage management but found an
> odity in the input clock frequency for the PWM controller. It seems like RM
> is assuming an input clock of 27.648 MHz instead of the actual 27MHz crystal
> found on the board.
> 
> I thus have the following questions:
>  - Is it a fixed value hardcoded in RM? (Current way it is done in Nouveau)
>  - Should we use crystal_MHz * 1.024?
> 
> I could spend some time hooking up my osciloscope to the VR to check if it
> is a bringup issue but it would not help Nouveau much as we need to
> reproduce the behaviour of RM anyway since this is the only validated
> configuration.
> 
> Thanks in advance,
> Martin
> 
> PS: The registers for this PWM controller are 0x20340 and 0x20344.