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

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

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@oss.qualcomm.com>
>>> ---
>>>    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.

> 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?

  Tomi