[0/2] dt-bindings: List supplies needed for sc7280 eDP

While looking through dts changes for sc7280 eDP I found that none of
the regulators that were being defined were listed in the
bindings. That being said, the current Linux drivers _were_ looking
for regulators. This series tries to document the reality to the best
of my ability.

If someone from Qualcomm has better documentation than I do and wants
to correct anything here then I'd be more than happy. For the PHY
patch especially I don't have a great way to map what I see in
datasheets / schematics to figure out which is the supply for the
"phy" and the "pll".

Assuming these look OK, I'd expect the PHY patch to land through the
PHY tree and the display patch to land through msm-next. I can split
the series up if need be--the two patches are just in one series
because they have a similar topic--there are no actual dependencies
here.


Douglas Anderson (2):
  dt-bindings: msm/dp: List supplies in the bindings
  dt-bindings: phy: List supplies for qcom,edp-phy

 .../devicetree/bindings/display/msm/dp-controller.yaml      | 6 ++++++
 Documentation/devicetree/bindings/phy/qcom,edp-phy.yaml     | 6 ++++++
 2 files changed, 12 insertions(+)

Hi,

On Mon, Apr 25, 2022 at 2:14 PM Stephen Boyd <swboyd@chromium.org> wrote:
>
> Quoting Douglas Anderson (2022-04-25 14:06:42)
> > We're supposed to list the supplies in the dt bindings but there are
> > none in the DP controller bindings. Looking at the Linux driver and
> > existing device trees, we can see that two supplies are expected:
> > - vdda-0p9-supply
> > - vdda-1p2-supply
> >
> > Let's list them both in the bindings. Note that the datasheet for
> > sc7280 doesn't describe these supplies very verbosely. For the 0p9
> > supply, for instance, it says "Power for eDP 0.9 V circuits". This
> > this is obvious from the property name, we don't bother cluttering the
> > bindings with a description.
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > ---
> >
> >  .../devicetree/bindings/display/msm/dp-controller.yaml      | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/display/msm/dp-controller.yaml b/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
> > index cd05cfd76536..dba31108db51 100644
> > --- a/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
> > +++ b/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
> > @@ -76,6 +76,9 @@ properties:
> >    "#sound-dai-cells":
> >      const: 0
> >
> > +  vdda-0p9-supply: true
> > +  vdda-1p2-supply: true
> > +
> >    ports:
> >      $ref: /schemas/graph.yaml#/properties/ports
> >      properties:
> > @@ -137,6 +140,9 @@ examples:
> >
> >          power-domains = <&rpmhpd SC7180_CX>;
> >
> > +        vdda-0p9-supply = <&vdda_usb_ss_dp_core>;
>
> 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.
>>
>
>That sounds like USB-DP combo phy driver had improper regulator power
>management where aux transactions from DP didn't keep the power on to
>the phy. Where does the power physically go? If the power isn't physically
>going to the DP controller it shouldn't be controlled from the DP controller
>driver. If the aux bus needs the DP phy enabled, the DP controller driver
>should enable the phy power (via phy_power_on()?).

Yes, it was limitation earlier when we did not have proper interface to interact
with the combo phy.

In this case, the power from the regulators go to the combo phy.

Now that there is an interface for the controller to interact with the
combo phy, the proposal to drop the phy regulator voting from the controller
driver seems reasonable to me.

The phy_power_on() is used for getting the phy out of low power state or getting
it ready for data transfer.

The controller driver needs to enable the phy power via the phy_init() before
any interaction with the sink like the aux transactions or before sending the data.
The controller can disable the regulators via the phy_exit() call.

Thank you,
Sankeerth

Hi,

On Fri, May 6, 2022 at 6:36 AM Sankeerth Billakanti (QUIC)
<quic_sbillaka@quicinc.com> wrote:
>
> >> >> 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.
> >>
> >
> >That sounds like USB-DP combo phy driver had improper regulator power
> >management where aux transactions from DP didn't keep the power on to
> >the phy. Where does the power physically go? If the power isn't physically
> >going to the DP controller it shouldn't be controlled from the DP controller
> >driver. If the aux bus needs the DP phy enabled, the DP controller driver
> >should enable the phy power (via phy_power_on()?).
>
> Yes, it was limitation earlier when we did not have proper interface to interact
> with the combo phy.
>
> In this case, the power from the regulators go to the combo phy.
>
> Now that there is an interface for the controller to interact with the
> combo phy, the proposal to drop the phy regulator voting from the controller
> driver seems reasonable to me.
>
> The phy_power_on() is used for getting the phy out of low power state or getting
> it ready for data transfer.
>
> The controller driver needs to enable the phy power via the phy_init() before
> any interaction with the sink like the aux transactions or before sending the data.
> The controller can disable the regulators via the phy_exit() call.

I can confirm that if I stop providing these regulators to the DP
controller that the screen still comes up. ...but also there are lots
of other things (including the PHY) that power these regulators up...