Re: [PATCH 2/2] drm/bridge: display-connector: trigger initial HPD event for DP

[Dmitry Baryshkov]

Hi,

On Wed, 18 Mar 2026 at 19:40, Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>

Sorry, I missed your email.

>
> On Sat, Mar 14, 2026 at 02:43:12AM +0200, Dmitry Baryshkov wrote:
> > If the DisplayPort drivers use display-connector for the HPD detection,
> > the internal HPD state machine might be not active and thus the hardware
> > might be not able to handle cable detection correctly. Instead it will
> > depend on the externall HPD notifications to set the cable state,
> > bypassing the internal HPD state machine (for example this is the case
> > for the msm DP driver).
> >
> > However if the cable has been plugged before the HPD IRQ has been
> > enabled, there will be no HPD event coming. The drivers might fail
> > detection in such a case. Trigger the HPD notification after enabling
> > the HPD IRQ, propagating the cable insertion state.
>
> The explanation makes sense, but it sounds like to could apply the same
> way to HDMI. What am I missing ?

Well... First of all, since HDMI doesn't have all DP magic, there is
no difference between HPD pin state and the display being plugged in
(so, e.g. dp-connector can't implement OP_DETECT, while hdmi-connector
does). For HDMI we usually don't have a complicated state machine in
the hardware. Nor do we have a an AUX bus with timeouts, etc.

>
> Also, wouldn't it be better if the DRM core interrogated the state of
> the HPD signal when enabling HPD, instead of relying on all drivers to
> implement something similar as this patch ?

Most of the drivers don't require this. It is only limited to the
OP_HPD bridges which don't implement OP_DETECT.

>
> > Fixes: 2e2bf3a5584d ("drm/bridge: display-connector: add DP support")
> > Reported-by: Yongxing Mou <yongxing.mou@xxxxxxxxxxxxxxxx>
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/bridge/display-connector.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)



--
With best wishes
Dmitry