Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Content-Type: text/plain;
        charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.21\))
Subject: Re: [Letux-kernel] [PATCH v16 1/4] drm/bridge: dw-hdmi: introduce
 dw_hdmi_enable_poll()
From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <02FDA8C2-68FD-4EB8-9846-AF510D16424D@goldelico.com>
Date:   Sat, 5 Mar 2022 08:49:56 +0100
Cc:     Paul Boddie <paul@boddie.org.uk>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Maxime Ripard <maxime@cerno.tech>,
        Jonas Karlman <jonas@kwiboo.se>,
        David Airlie <airlied@linux.ie>,
        Robert Foss <robert.foss@linaro.org>,
        linux-mips <linux-mips@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@openphoenux.org>
Content-Transfer-Encoding: quoted-printable
Message-Id: <C61F337D-7325-43BA-AFF1-A6E7FD602693@goldelico.com>
References: <cover.1645895582.git.hns@goldelico.com>
 <e54838849f80454b863f9f5634dd10f79ef7bb8f.1645895582.git.hns@goldelico.com>
 <983e9064-17ad-e646-f37d-ca9173ba0967@baylibre.com>
 <C8AE9A7A-E288-4637-ACAD-40CD33CD5F8C@goldelico.com>
 <3E620AF4-402E-45EA-9D92-92EAEA9647F5@goldelico.com>
 <SHH68R.Z3J9KSY0GQVA2@crapouillou.net>
 <ABC1BD09-383B-4499-B034-340CE88725B3@goldelico.com>
 <RUI68R.Z009SPJAAD8N1@crapouillou.net>
 <F0F8F36B-3A0A-476C-8C7D-566255C629C6@goldelico.com>
 <a52702bd-c929-8170-8896-d34ba82aba3c@baylibre.com>
 <VYB88R.ATGIVGZ13PFM1@crapouillou.net>
 <929BF693-D54F-40F0-BB61-520301D1C31F@goldelico.com>
 <8JF88R.9V5YQ3Q6E8QO2@crapouillou.net>
 <5CC8B441-AA50-45F5-A5D3-2F40F72A1B50@goldelico.com>
 <NWG88R.ZTPBZB4D9J5Z@crapouillou.net>
 <02FDA8C2-68FD-4EB8-9846-AF510D16424D@goldelico.com>
To:     Paul Cercueil <paul@crapouillou.net>
Precedence: bulk

Hi Paul,

> Am 04.03.2022 um 19:41 schrieb H. Nikolaus Schaller =
<hns@goldelico.com>:
>=20
>=20
>=20
>> Am 04.03.2022 um 19:33 schrieb Paul Cercueil <paul@crapouillou.net>:
>>=20
>>=20
>>=20
>> Le ven., mars 4 2022 at 19:15:13 +0100, H. Nikolaus Schaller =
<hns@goldelico.com> a =C3=A9crit :
>>> 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 =C3=A9crit :
>>>>> Hi Paul, Neil,
>>>>>> Am 04.03.2022 um 17:47 schrieb Paul Cercueil =
<paul@crapouillou.net>:
>>>>>> =46rom 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/dc=
ss-dev.c#L292
>>> =
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/imx/dcss/dc=
ss-kms.c#L145
>>> =
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/omapdrm/oma=
p_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@cogentem=
bedded.com/T/
>>=20
>> Looks correct to me. It has been reviewed by two people so I believe =
it will be merged very soon.
>=20
> Great. I will try asap. If it works we can drop all our private =
ideas...
>=20
> And focus on the last missing piece for jz4780 HDMI: the output format =
negotiation (which still is not working properly - but I have to analyse =
why).

Yes, it works. And I see you have merged it to drm-misc-next so that I =
can build on it.

So there is only the bus format negotiation to be understood and finally =
solved for v17.

Great and thanks,
Nikolaus