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

From: "Sankeerth Billakanti (QUIC)" <quic_sbillaka@quicinc.com>
To: Stephen Boyd <swboyd@chromium.org>,
	Doug Anderson <dianders@chromium.org>
Cc: "bjorn.andersson@linaro.org" <bjorn.andersson@linaro.org>,
	"dmitry.baryshkov@linaro.org" <dmitry.baryshkov@linaro.org>,
	Rob Clark <robdclark@chromium.org>,
	Rob Herring <robh+dt@kernel.org>, Vinod Koul <vkoul@kernel.org>,
	"Abhinav Kumar (QUIC)" <quic_abhinavk@quicinc.com>,
	"linux-phy@lists.infradead.org" <linux-phy@lists.infradead.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	freedreno <freedreno@lists.freedesktop.org>,
	Kishon Vijay Abraham I <kishon@ti.com>,
	"Sankeerth Billakanti (QUIC)" <quic_sbillaka@quicinc.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	"Kalyan Thota (QUIC)" <quic_kalyant@quicinc.com>,
	"Kuogee Hsieh (QUIC)" <quic_khsieh@quicinc.com>,
	Daniel Vetter <daniel@ffwll.ch>, David Airlie <airlied@linux.ie>,
	Rob Clark <robdclark@gmail.com>, Sean Paul <sean@poorly.run>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 1/2] dt-bindings: msm/dp: List supplies in the bindings
Date: Thu, 5 May 2022 18:47:20 +0000	[thread overview]
Message-ID: <MW4PR02MB71867A18732B266DE8FA2040E1C29@MW4PR02MB7186.namprd02.prod.outlook.com> (raw)
In-Reply-To: <CAE-0n51Q=cGwrMec3JEQENqWHV3pAUjLPT6RwZLA5xV080sgxQ@mail.gmail.com>

>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@quicinc.com>
>>