linux-kernel - Re: [Letux-kernel] [PATCH v16 1/4] drm/bridge: dw-hdmi: introduce dw_hdmi_enable

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Message-Id: <5CC8B441-AA50-45F5-A5D3-2F40F72A1B50@goldelico.com>
Date:   Fri, 4 Mar 2022 19:15:13 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        Paul Boddie <paul@...die.org.uk>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Maxime Ripard <maxime@...no.tech>,
        Jonas Karlman <jonas@...boo.se>,
        David Airlie <airlied@...ux.ie>,
        Robert Foss <robert.foss@...aro.org>,
        linux-mips <linux-mips@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>
Subject: Re: [Letux-kernel] [PATCH v16 1/4] drm/bridge: dw-hdmi: introduce
 dw_hdmi_enable_poll()

Hi Paul,

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

BR and thanks,
Nikolaus