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


Le ven., mars 4 2022 at 19:15:13 +0100, H. Nikolaus Schaller
<hns@goldelico.com> a écrit :
> Hi Paul,
>
>> Am 04.03.2022 um 19:04 schrieb Paul Cercueil <paul@crapouillou.net>:
>>
>>
>>
>> Le ven., mars 4 2022 at 18:51:14 +0100, H. Nikolaus Schaller
>> <hns@goldelico.com> a écrit :
>>> Hi Paul, Neil,
>>>> Am 04.03.2022 um 17:47 schrieb Paul Cercueil
>>>> <paul@crapouillou.net>:
>>>> 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@cogentembedded.com/T/

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

Cheers,
-Paul


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