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

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Message-Id: <8JF88R.9V5YQ3Q6E8QO2@crapouillou.net>
Date:   Fri, 04 Mar 2022 18:04:20 +0000
From:   Paul Cercueil <paul@...pouillou.net>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
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()



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.

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().

Cheers,
-Paul

> 
> 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.
> 
> So I think it should not be solved outside dw-hdmi.
> 
> BR and thanks,
> Nikolaus
>