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

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Date:   Fri, 4 Mar 2022 18:51:14 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Paul Cercueil <paul@...pouillou.net>,
        Neil Armstrong <narmstrong@...libre.com>
Cc:     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, 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.

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