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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <b4983b93-97fc-43ed-a41c-a44f90773062@oss.qualcomm.com>
Date: Mon, 31 Mar 2025 18:49:18 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Christopher Obbard <christopher.obbard@...aro.org>,
        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>,
        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

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.

> I will add a short comment about how the hpd signal is handled by the
> driver already.

-- 
With best wishes
Dmitry