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

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On 31/03/2025 18:39, Christopher Obbard wrote:
> Hi Johan,
> 
> On Mon, 31 Mar 2025 at 09:50, Johan Hovold <johan@kernel.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@linaro.org>
>>> Signed-off-by: Christopher Obbard <christopher.obbard@linaro.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