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-zFDDPfRXZYUsbMoBASU6O5mBmqiFNFBtZTL9_vbo_7uANg@mail.gmail.com>
Date: Mon, 31 Mar 2025 23:38:39 +0200
From: Christopher Obbard <christopher.obbard@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Johan Hovold <johan@...nel.org>, 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>, 
	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 Dmitry,

On Mon, 31 Mar 2025 at 17:49, Dmitry Baryshkov
<dmitry.baryshkov@....qualcomm.com> wrote:
>
> On 31/03/2025 18:39, Christopher Obbard wrote:
> > 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.
> No, you won't. There is a HPD line and it is routed to the DP controller.

OK, I think I misunderstand what Johan said. After taking some time to
think about it in more detail:
- The first commit will be changed so that the hpd GPIO will be added
to the X1E DP controller instead of the panel. grepping the source for
dp_hot_plug_det shows me how to do that. This part is clear.

- The panel node in the generic T14s DTSI should not have the
hpd-gpios property / pinctrl set.

- The panel node should not have the hpd-gpios property / pinctrl set.

I hope I understand that correctly. I will send a new series in the
morning unless there is any objection.

Thanks

Chris