RE: [PATCH 1/2] dt-bindings: msm/dp: List supplies in the bindings

[Sankeerth Billakanti (QUIC)]

>Quoting Sankeerth Billakanti (2022-05-05 11:02:36)
>> >>
>> >> Quoting Douglas Anderson (2022-04-25 14:06:42)
>> >>
>> >> Having 'a' in 'vdda' typically means 'analog' for 'analog'
>> >> circuits, so I'd expect this to only matter for the phy that
>> >> contains the analog circuitry. It would be great to remove the
>> >> regulator code from drivers/gpu/drm/msm/dp/dp_power.c and move
>the
>> >> regulator_set_load() call to the phy driver if possible. Hopefully
>> >> qcom folks can help clarify here.
>> >
>> >Interesting. Oddly enough, the sc7280 datasheet doesn't list the "_A".
>> >It calls these "VDD_VREF_0P9" and "VDD_VREF_1P2". However, on the
>> >schematic in front of me someone labeled these pins on the sc7280
>> >with the "A". ...and the driver looks for a supply with the "a". :-/
>> >
>> >It would be good to get clarification from someone with better
>information.
>> >
>> >-Doug
>>
>> Our internal power grid documents list the regulators as VDD_A_*_1P2
>> and VDD_A_*_0P9 for all the platforms.
>
>Do your internal power grid documents indicate what these supplies are
>powering? The question is if these supplies power any of the logic inside the
>eDP controller or if they only supply power to the analog circuits in the eDP
>phy. If it's the eDP phy only then the regulator usage in the eDP driver should
>be removed. I would suspect this is the case because the controller is
>probably all digital logic and runs at the typical 1.8V that the rest of the SoC
>uses. Similarly, these are voltage references which sound like a PLL reference
>voltage.
>
>Please clarify this further.
>

For the DP driver using the usb-dp combo phy, there were cases where the usb driver
was turning off the phy and pll regulators whenever usb-dp concurrent mode need not be supported.
This caused phy and pll to be powered down causing aux transaction failures and display blankouts. 
From then on, it became a practice for the controller driver to vote for the phy and pll regulators also.

>>
>> So, as a practice, we put the same name in the DT files. Hence,
>>
>> Reviewed-by: Sankeerth Billakanti <quic_sbillaka@xxxxxxxxxxx>
>>