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

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Date:   Wed, 23 Feb 2022 16:17:22 +0000
From:   Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
To:     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 Laurent, Nikita,

Quoting Laurent Pinchart (2021-12-29 23:44:29)
> Hi Nikita,
> 
> Thank you for the patch.
> 
> 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>


> > In result, once encoders are switched to bridge_connector,
> > bridge-detected HPD stops working.
> > 
> > This patch adds a call to that API on init path.
> > 
> > This fixes HDMI HPD with rcar-du + adv7513 case when adv7513 reports HPD
> > events via interrupts.
> > 
> > Fixes: c24110a8fd09 ("drm: rcar-du: Use drm_bridge_connector_init() helper")
> > Signed-off-by: Nikita Yushchenko <nikita.yoush@...entembedded.com>
> > ---
> >  drivers/gpu/drm/drm_bridge_connector.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_bridge_connector.c b/drivers/gpu/drm/drm_bridge_connector.c
> > index 791379816837..4f20137ef21d 100644
> > --- a/drivers/gpu/drm/drm_bridge_connector.c
> > +++ b/drivers/gpu/drm/drm_bridge_connector.c
> > @@ -369,8 +369,10 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
> >                                   connector_type, ddc);
> >       drm_connector_helper_add(connector, &drm_bridge_connector_helper_funcs);
> >  
> > -     if (bridge_connector->bridge_hpd)
> > +     if (bridge_connector->bridge_hpd) {
> >               connector->polled = DRM_CONNECTOR_POLL_HPD;
> > +             drm_bridge_connector_enable_hpd(connector);
> > +     }
> >       else if (bridge_connector->bridge_detect)
> >               connector->polled = DRM_CONNECTOR_POLL_CONNECT
> >                                 | DRM_CONNECTOR_POLL_DISCONNECT;
> 
> -- 
> Regards,
> 
> Laurent Pinchart