Re: [PATCH v2 07/12] drm/msm/hdmi: enable core-vcc/core-vdda-supply for 8996 platform

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

On Thu, 9 Jun 2022 at 00:02, Stephen Boyd <swboyd@chromium.org> wrote:
>
> Quoting Dmitry Baryshkov (2022-06-08 05:07:18)
> > DB820c makes use of core-vcc-supply and core-vdda-supply, however the
> > driver code doesn't support these regulators. Enable them for HDMI on
> > 8996 platform.
>
> The 'vdda-supply' name makes me think this is another scenario where the
> phy isn't powering on the analog supply when it should be and so the
> controller driver is doing it instead. Is that the case here?

Good question. There are different HDMI pins on 8996, with slight
disagreement between the schematics and the datasheet.
vcca_hdmi/vdd_hdmi1: 0.925V, Power for HDMI circuits – low voltage
vdda_hdmi/vdd_hdmi2: 1.8V, Power for HDMI circuits – high voltage
vdda_hdmi_pll/vdd_pll3, 1.8V, Power for PLL circuits

I'm not sure which are required for the PHY and which are required for
the core HDMI. However I'd note that we have a generic tendency of
duplicating pins between the HDMI and the PHY devices. Compare this
with 8064, where core-vdda-supply is also used both by the hdmi-tx and
hdmi-phy devices. I think we unify 8x74/84 with 8996 and allow
powering up the HDMI correctly even if it results in duplication
between the -phy and -tx parts.


-- 
With best wishes
Dmitry