Re: [PATCH 1/6] drm/connector: report IRQ_HPD events to drm_connector_oob_hotplug_event()

[Dmitry Baryshkov]

On Mon, Apr 20, 2026 at 07:50:46AM +0300, Tomi Valkeinen wrote:
> Hi,
> 
> On 18/04/2026 01:32, Dmitry Baryshkov wrote:
> > On Thu, Apr 16, 2026 at 11:10:03AM +0300, Tomi Valkeinen wrote:
> > > Hi,
> > > 
> > > On 16/04/2026 02:22, Dmitry Baryshkov wrote:
> > > > The DisplayPort standard defines a special kind of events called IRQ.
> > > > These events are used to notify DP Source about the events on the Sink
> > > > side. It is extremely important for DP MST handling, where the MST
> > > > events are reported through this IRQ.
> > > > 
> > > > In case of the USB-C DP AltMode there is no actual HPD pulse, but the
> > > > events are ported through the bits in the AltMode VDOs.
> > > > 
> > > > Extend the drm_connector_oob_hotplug_event() interface and report IRQ
> > > > events to the DisplayPort Sink drivers.
> > > > 
> > > > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
> > > > ---
> > > >    drivers/gpu/drm/drm_connector.c          |  4 +++-
> > > >    drivers/usb/typec/altmodes/displayport.c | 12 ++++++++----
> > > >    include/drm/drm_connector.h              |  3 ++-
> > > >    3 files changed, 13 insertions(+), 6 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> > > > index 47dc53c4a738..5fdacbd84bd7 100644
> > > > --- a/drivers/gpu/drm/drm_connector.c
> > > > +++ b/drivers/gpu/drm/drm_connector.c
> > > > @@ -3510,6 +3510,7 @@ struct drm_connector *drm_connector_find_by_fwnode(struct fwnode_handle *fwnode)
> > > >     * drm_connector_oob_hotplug_event - Report out-of-band hotplug event to connector
> > > >     * @connector_fwnode: fwnode_handle to report the event on
> > > >     * @status: hot plug detect logical state
> > > > + * @irq_hpd: HPD pulse detected
> > > >     *
> > > >     * On some hardware a hotplug event notification may come from outside the display
> > > >     * driver / device. An example of this is some USB Type-C setups where the hardware
> > > > @@ -3520,7 +3521,8 @@ struct drm_connector *drm_connector_find_by_fwnode(struct fwnode_handle *fwnode)
> > > >     * a drm_connector reference through calling drm_connector_find_by_fwnode().
> > > >     */
> > > >    void drm_connector_oob_hotplug_event(struct fwnode_handle *connector_fwnode,
> > > > -				     enum drm_connector_status status)
> > > > +				     enum drm_connector_status status,
> > > > +				     bool irq_hpd)
> > > I find the "IRQ HPD" naming always confusing, even if I'm somewhat familiar
> > > with DP, but if someone has mainly worked on HDMI, I'm sure it's even worse.
> > > 
> > > Can we define this a bit more precisely? Is 'irq_hpd' only for displayport?
> > > If so, perhaps 'dp_irq_hpd' or 'displayport_irq_hpd'. I might even call it
> > > 'dp_hpd_pulse', but maybe that's not good as the spec talks about HPD pulse
> > > for both short and long ones (although in the kernel doc you just write "HPD
> > > pulse")... The kernel doc could be expanded a bit to make it clear what this
> > > flag indicates.
> > 
> > I attempted to stay away from defining a DP-specific flag, keeping it
> > generic enough. HDMI is pretty close (IMO) to requiring separate flag in
> 
> If it's not specifically the DP IRQ HPD, then we need to define what it
> means. I tried to think what it would mean with HDMI, but I didn't come up
> with anything.

I might be mistaken, but I had someting like HEAC HPD / EDID status
changes in mind (or HDCP-triggered HPD status changes). But here I
admit, I hadn't checked if it is actually applicable or not.

Anyway, for e.g. DVI or VGA that means nothing. But, my point really is
to abstain from defining someting as DP-only in the top-level API.

> 
> > Linux. Likewise I'd rather not use "pulse". The DP AltMode defines a bit
> > in the VDO rather than a pulse.
> > 
> > Anyway, if irq_hpd doesn't sound precise enough, what about "bool
> > extra_irq"? This would convey that this is the extra hpd-related IRQ,
> > but it would also be obvious that it's not related to the HPD pin
> > itself.
> We'd still need to define what exactly it means. I think it might be better
> to just define it as the DP IRQ HPD, as then the meaning is clear.
> 
> Also, would an enum flags parameter be better than a bool parameter?

Maybe not enum, but u32 param. Then it can become:

@extra_status: additional type-specific information provided by the sink
without changing the HPD state

void drm_connector_oob_hotplug_event(..., u32 extra_status);

/* DP short HPD pulse or corresponding AltMode flag */
#define DRM_CONNECTOR_OOB_DP_IRQ_HPD BIT(0)
/* DP long HPD pulse, debounced XXX: do we need this? */
#define DRM_CONNECTOR_OOB_DP_REPLUG BIT(1)

For HDMI we might want to define:

/* HDMI 1.4b 8.5, HPD pulse */
#define DRM_CONNECTOR_OOB_HDMI_REPLUG BIT(0)

Or might not, 100ms is long enough for all debouncers.

For HDMI we potentially have another source of OOB events, CDC-messages
from CEC controller. I have not looked in the details of the HEAC 3.

-- 
With best wishes
Dmitry