Hi Tim,

On Thu, Oct 01, 2020 at 11:15:46AM +0100, Tim Gover wrote:
> hdmi_enable_4k60=1 causes the firmware to select 3.3 GHz for the PLLC
> VCO to support a core-frequency of 550 MHz which is the minimum
> frequency required by the HVS at 4Kp60. The side effect is that if the
> display clock requirements are lower than 4Kp60 then you will see
> different core frequencies selected by DVFS.
> 
> If enable_uart=1 and the mini-uart is selected (default unless
> bluetooth is disabled) then the firmware will pin the core-frequency
> to either core_freq max (500 or 550). Although, I think there is a way
> of pinning it to a lower fixed frequency.
> 
> The table in overclocking.md defines options for setting the maximum
> core frequency but unless core_freq_min is specified DVFS will
> automatically pick the lowest idle frequency required by the display
> resolution.

I'm wondering if there's some way to detect this from Linux? I guess it
would be nice to be able to at least detect a broken config to warn /
prevent an user that their situation is not going to be reliable / work
really well (like if they have a 4k display without hdmi_enable_4kp60
set, or the issue we're discussing here)

Thanks!
Maxime