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

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Date:   Thu, 3 Mar 2022 18:05:45 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Paul Cercueil <paul@...pouillou.net>,
        Neil Armstrong <narmstrong@...libre.com>
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Robert Foss <robert.foss@...aro.org>,
        Paul Boddie <paul@...die.org.uk>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maxime Ripard <maxime@...no.tech>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>,
        linux-mips <linux-mips@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Jonas Karlman <jonas@...boo.se>
Subject: Re: [PATCH v16 1/4] drm/bridge: dw-hdmi: introduce
 dw_hdmi_enable_poll()

Hi Paul and Neil,

> Am 03.03.2022 um 17:46 schrieb Paul Cercueil <paul@...pouillou.net>:
> 
> Hi Neil,
> 
> Le jeu., mars 3 2022 at 17:23:02 +0100, Neil Armstrong <narmstrong@...libre.com> a écrit :
>> Hi,
>> On 26/02/2022 18:12, H. Nikolaus Schaller wrote:
>>> so that specialization drivers like ingenic-dw-hdmi can enable polling.
>>> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
>>> ---
>>>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 9 +++++++++
>>>  include/drm/bridge/dw_hdmi.h              | 1 +
>>>  2 files changed, 10 insertions(+)
>>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>>> index 4befc104d2200..43e375da131e8 100644
>>> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
>>> @@ -3217,6 +3217,15 @@ static int dw_hdmi_parse_dt(struct dw_hdmi *hdmi)
>>>  	return 0;
>>>  }
>>>  +void dw_hdmi_enable_poll(struct dw_hdmi *hdmi, bool enable)
>>> +{
>>> +	if (hdmi->bridge.dev)
>>> +		hdmi->bridge.dev->mode_config.poll_enabled = enable;
>>> +	else
>>> +		dev_warn(hdmi->dev, "no hdmi->bridge.dev");
>>> +}
>>> +EXPORT_SYMBOL_GPL(dw_hdmi_enable_poll);
>>> +
>>>  struct dw_hdmi *dw_hdmi_probe(struct platform_device *pdev,
>>>  			      const struct dw_hdmi_plat_data *plat_data)
>>>  {
>>> diff --git a/include/drm/bridge/dw_hdmi.h b/include/drm/bridge/dw_hdmi.h
>>> index 2a1f85f9a8a3f..963960794b40e 100644
>>> --- a/include/drm/bridge/dw_hdmi.h
>>> +++ b/include/drm/bridge/dw_hdmi.h
>>> @@ -196,5 +196,6 @@ enum drm_connector_status dw_hdmi_phy_read_hpd(struct dw_hdmi *hdmi,
>>>  void dw_hdmi_phy_update_hpd(struct dw_hdmi *hdmi, void *data,
>>>  			    bool force, bool disabled, bool rxsense);
>>>  void dw_hdmi_phy_setup_hpd(struct dw_hdmi *hdmi, void *data);
>>> +void dw_hdmi_enable_poll(struct dw_hdmi *hdmi, bool enable);
>>>    #endif /* __IMX_HDMI_H__ */
>> As I understand, this is because the IRQ line of the dw-hdmi IP isn't connected right ? and you use the display-connector ddc gpio instead ?

Ah, I should finish work for today since I am no longer reading every word properly...

No, we do NOT use the display connector for HPD. We use HPD of the dw-hdmi.
Either IRQ is not enabled properly or not working in IRQ mode.
But it works if polling is enabled.

> 
> According to the CI20 schematic, it is wired properly. So that's strange.

Yes, HTPLG input goes through an 1kΩ + 1µF low-pass filter to debounce HDMI_HTPLG.
This goes to the HPD (BGA ball N19).
There is an optional Q14 driving HDMI_DETE_N.
This could become the hpd-gpios property of the connector in the device tree.
But it is optional.

So we have to use dw-hdmi HPD and make it work (in combination with a chained hdmi-connector).

> 
>> In this case I think the Ingenic DRM core should call drm_kms_helper_poll_init(drm) instead.
> 
> Yes, the ingenic-drm driver does not poll for connectors because until now it never has been needed.

Well, if we go back a while we only needed it after introducing the hdmi-connectors
and making dw-hdmi a bridge.

Originally the dw-hdmi driver did properly take care of everything (by registering its own connector).

BR and thanks,
Nikolaus