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

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Message-ID: <YhZf+Fs2AP+btuJj@pendragon.ideasonboard.com>
Date:   Wed, 23 Feb 2022 18:25:28 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
Cc:     Nikita Yushchenko <nikita.yoush@...entembedded.com>,
        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

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>

> > > 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