Re: [Letux-kernel] [PATCH v16 1/4] drm/bridge: dw-hdmi: introduce dw_hdmi_enable_poll()

[Paul Cercueil]

Le ven., mars 4 2022 at 19:15:13 +0100, H. Nikolaus Schaller 
<hns@xxxxxxxxxxxxx> a écrit :
> Hi Paul,
>
> >  Am 04.03.2022 um 19:04 schrieb Paul Cercueil <paul@xxxxxxxxxxxxxxx>:
> >
> >
> >
> >  Le ven., mars 4 2022 at 18:51:14 +0100, H. Nikolaus Schaller 
> > <hns@xxxxxxxxxxxxx> a écrit :
> > >  Hi Paul, Neil,
> > > >  Am 04.03.2022 um 17:47 schrieb Paul Cercueil 
> > > > <paul@xxxxxxxxxxxxxxx>:
> > > >  From what I understood in Nikolaus' last message, HDMI hotplug is 
> > > > actually correctly detected, so there's no need for polling. What 
> > > > is missing is the call to drm_kms_helper_hotplug_event 
> > > > *somewhere*, so that the information is correctly relayed to 
> > > > userspace.
> > >  Exactly.
> > >  As Maxime pointed out it should already be called by 
> > > drm_helper_hpd_irq_event() in dw_hdmi_irq() but isn't
> > >  because mode_config.poll_enabled isn't enabled.
> > >  So we can either
> > >  a) enable mode_config.poll_enabled so that it is called by 
> > > drm_helper_hpd_irq_event() or
> > >  b) make drm_kms_helper_hotplug_event() being called explicitly in 
> > > dw_hdmi_irq().
> > >    We could guard that by mode_config.poll_enabled to avoid 
> > > drm_kms_helper_hotplug_event()
> > >    being called twice (but I think the "changed" mechanism will 
> > > take care of).
> > > >  I think this issue can be fixed by calling 
> > > > drm_bridge_connector_enable_hpd() on the connector in 
> > > > ingenic-drm-drv.c.
> > >  I don't see yet how this would solve it, but it may work.
> >
> >  dw_hdmi_irq() calls drm_bridge_hpd_notify(), which would call 
> > bridge->hpd_cb() if it was non-NULL.
>
> Ok, this is a case c).
>
> I vaguely remember having tried to analyse what bridge->hpd_cb is but 
> stopped since it is NULL...
>
> >  Calling drm_bridge_connector_enable_hpd() will set the 
> > bridge->hpd_cb() callback to point to drm_bridge_connector_hpd_cb(), 
> > which itself will call drm_kms_helper_hotplug_event(). Therefore, 
> > all that is missing is one call to drm_bridge_connector_enable_hpd().
>
> Ah, ok, I see.
>
> > >  Anyways, this all is a missing feature (sometimes called "bug") of 
> > > the *dw-hdmi driver* and IMHO
> > >  neither of the connector nor the ingenic-drm-drv.
>
> Well, a little more analysis shows that 
> drm_bridge_connector_enable_hpd is called
> in the *-drv.c for some other plaforms:
>
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/imx/dcss/dcss-dev.c#L292
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/imx/dcss/dcss-kms.c#L145
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/omapdrm/omap_drv.c#L393
> https://elixir.bootlin.com/linux/v5.17-rc6/source/drivers/gpu/drm/msm/hdmi/hdmi.c#L317
>
> > >  So I think it should not be solved outside dw-hdmi.
>
> Hm. Can we call drm_bridge_connector_enable_hpd() from inside dw-hdmi?
>
> Or would this be the solution if merged? (I currently can't try code).
>
> https://lore.kernel.org/lkml/a7d0b013-6114-07b3-0a7b-0d17db8a3982@xxxxxxxxxxxxxxxxxx/T/

Looks correct to me. It has been reviewed by two people so I believe it 
will be merged very soon.

Cheers,
-Paul