linux-kernel - Re: [PATCH] drm/bridge_connector: enable HPD by default if supported

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Message-ID: <7163f30b-6496-5762-0d9d-96834fb7452d@ideasonboard.com>
Date:   Wed, 31 Aug 2022 16:02:24 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Nikita Yushchenko <nikita.yoush@...entembedded.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge_connector: enable HPD by default if supported

Hi,

On 23/02/2022 19:02, Kieran Bingham wrote:
> Quoting Laurent Pinchart (2022-02-23 16:25:28)
>> Hello,
>>
>> On Wed, Feb 23, 2022 at 04:17:22PM +0000, Kieran Bingham wrote:
>>> Quoting Laurent Pinchart (2021-12-29 23:44:29)
>>>> On Sat, Dec 25, 2021 at 09:31:51AM +0300, Nikita Yushchenko wrote:
>>>>> Hotplug events reported by bridge drivers over drm_bridge_hpd_notify()
>>>>> get ignored unless somebody calls drm_bridge_hpd_enable(). When the
>>>>> connector for the bridge is bridge_connector, such a call is done from
>>>>> drm_bridge_connector_enable_hpd().
>>>>>
>>>>> However drm_bridge_connector_enable_hpd() is never called on init paths,
>>>>> documentation suggests that it is intended for suspend/resume paths.
>>>>
>>>> Hmmmm... I'm in two minds about this. The problem description is
>>>> correct, but I wonder if HPD should be enabled unconditionally here, or
>>>> if this should be left to display drivers to control.
>>>> drivers/gpu/drm/imx/dcss/dcss-kms.c enables HPD manually at init time,
>>>> other drivers don't.
>>>>
>>>> It feels like this should be under control of the display controller
>>>> driver, but I can't think of a use case for not enabling HPD at init
>>>> time. Any second opinion from anyone ?
>>>
>>> This patch solves an issue I have where I have recently enabled HPD on
>>> the SN65DSI86, but without this, I do not get calls to my .hpd_enable or
>>> .hpd_disable hooks that I have added to the ti_sn_bridge_funcs.
>>>
>>> So it needs to be enabled somewhere, and this seems reasonable to me?
>>> It's not directly related to the display controller - as it's a factor
>>> of the bridge?
>>>
>>> On Falcon-V3U with HPD additions to SN65DSI86:
>>> Tested-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
>>
>> If you think this is right, then
>>
>> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> 
> I do, and at the very least it works for me, and fixes Nikita's issue so
> to me that's enough for:

So who disables the HPD now?

Is the drm_bridge_connector_enable_hpd & 
drm_bridge_connector_disable_hpd documentation now wrong as they talk 
about suspend/resume handlers?

  Tomi