linux-kernel - Re: [PATCH v3 1/2] arm64: dts: qcom: x1e78100-t14s: add hpd gpio to eDP panel

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Message-ID: <CACr-zFA_oSySRnA2VaSQk2ND_AHeyt3v=RuPTbABPM7SYown6g@mail.gmail.com>
Date: Mon, 31 Mar 2025 17:39:35 +0200
From: Christopher Obbard <christopher.obbard@...aro.org>
To: Johan Hovold <johan@...nel.org>
Cc: Douglas Anderson <dianders@...omium.org>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konradybcio@...nel.org>, 
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	Rui Miguel Silva <rui.silva@...aro.org>, Abel Vesa <abel.vesa@...aro.org>, devicetree@...r.kernel.org, 
	"Bryan O'Donoghue" <bryan.odonoghue@...aro.org>
Subject: Re: [PATCH v3 1/2] arm64: dts: qcom: x1e78100-t14s: add hpd gpio to
 eDP panel

Hi Johan,

On Mon, 31 Mar 2025 at 09:50, Johan Hovold <johan@...nel.org> wrote:
>
> On Thu, Mar 27, 2025 at 04:56:53PM +0000, Christopher Obbard wrote:
> > The eDP panel has an HPD GPIO. Describe it in the device tree
> > for the generic T14s model, as the HPD GPIO property is used in
> > both the OLED and LCD models which inherit this device tree.
>
> AFAICT, this patch is not correct as the hotplug detect signal is
> connected directly to the display controller on (these) Qualcomm SoCs
> and is already handled by its driver.
>
> Describing it as you do here leads to less accurate delays, see commits:
>
>         2327b13d6c47 ("drm/panel-edp: Take advantage of wait_hpd_asserted() in struct drm_dp_aux").
>         3b5765df375c ("drm/panel: atna33xc20: Take advantage of wait_hpd_asserted() in struct drm_dp_aux")
>
> Perhaps you lose some other functionality too.
>
> > Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
> > Signed-off-by: Christopher Obbard <christopher.obbard@...aro.org>
> > ---
> >  arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
> > index 962fb050c55c4fd33f480a21a8c47a484d0c82b8..46c73f5c039ed982b553636cf8c4237a20ba7687 100644
> > --- a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
> > +++ b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
> > @@ -980,8 +980,12 @@ &mdss_dp3 {
> >       aux-bus {
> >               panel: panel {
> >                       compatible = "edp-panel";
> > +                     hpd-gpios = <&tlmm 119 GPIO_ACTIVE_HIGH>;
> >                       power-supply = <&vreg_edp_3p3>;
> >
> > +                     pinctrl-0 = <&edp_hpd_n_default>;
> > +                     pinctrl-names = "default";
> > +
> >                       port {
> >                               edp_panel_in: endpoint {
> >                                       remote-endpoint = <&mdss_dp3_out>;
> > @@ -1286,6 +1290,13 @@ hall_int_n_default: hall-int-n-state {
> >               bias-disable;
> >       };
> >
> > +     edp_hpd_n_default: edp-hpd-n-state {
> > +             pins = "gpio119";
> > +             function = "gpio";
> > +             drive-strength = <2>;
> > +             bias-pull-up;
> > +     };
>
> I checked the firmware configuration for this pin on my T14s, which
> does not match what you have here. Instead the function is set to
> "edp0_hot" which forwards the signal to the display controller which
> already handles the signal on panel power on. (And there is also no
> internal pull up enabled).
>
> We may want to describe this pin configuration somewhere, but that's a
> separate issue.

Thanks for your review, I will send another version in coming days and
drop this first patch (adding hpd to the T14s DTSI).

As a consequence I will need to add no-hpd property to the panel node.
I will add a short comment about how the hpd signal is handled by the
driver already.

Thanks!

Chris