linux-kernel - Re: [PATCH] drm/bridge: Ignore -EPROBE

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Message-ID: <YWaJm4u5fWbLHIea@qwark.sigxcpu.org>
Date:   Wed, 13 Oct 2021 09:24:11 +0200
From:   Guido Günther <agx@...xcpu.org>
To:     Andrzej Hajda <andrzej.hajda@...il.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.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>,
        Jyri Sarha <jyri.sarha@....fi>,
        Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: Ignore -EPROBE_DEFER when bridge attach fails

Hi,
On Wed, Oct 13, 2021 at 08:48:32AM +0200, Andrzej Hajda wrote:
> On 12.10.2021 22:47, Guido Günther wrote:
> > Hi Laurent,
> > On Tue, Oct 12, 2021 at 11:17:07PM +0300, Laurent Pinchart wrote:
> > > Hi Guido,
> > > 
> > > Thank you for the patch.
> > > 
> > > On Tue, Oct 12, 2021 at 09:58:58PM +0200, Guido Günther wrote:
> > > > Otherwise logs are filled with
> > > > 
> > > >    [drm:drm_bridge_attach] *ERROR* failed to attach bridge /soc@...us@...00000/mipi-dsi@...0 0000 to encoder None-34: -517
> > > > 
> > > > when the bridge isn't ready yet.
> > > > 
> > > > Fixes: fb8d617f8fd6 ("drm/bridge: Centralize error message when bridge attach fails")
> > > > Signed-off-by: Guido Günther <agx@...xcpu.org>
> > > > ---
> > > >   drivers/gpu/drm/drm_bridge.c | 11 ++++++-----
> > > >   1 file changed, 6 insertions(+), 5 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > > > index a8ed66751c2d..f0508e85ae98 100644
> > > > --- a/drivers/gpu/drm/drm_bridge.c
> > > > +++ b/drivers/gpu/drm/drm_bridge.c
> > > > @@ -227,14 +227,15 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
> > > >   	bridge->encoder = NULL;
> > > >   	list_del(&bridge->chain_node);
> > > > +	if (ret != -EPROBE_DEFER) {
> > > >   #ifdef CONFIG_OF
> > > > -	DRM_ERROR("failed to attach bridge %pOF to encoder %s: %d\n",
> > > > -		  bridge->of_node, encoder->name, ret);
> > > > +		DRM_ERROR("failed to attach bridge %pOF to encoder %s: %d\n",
> > > > +			  bridge->of_node, encoder->name, ret);
> > > >   #else
> > > > -	DRM_ERROR("failed to attach bridge to encoder %s: %d\n",
> > > > -		  encoder->name, ret);
> > > > +		DRM_ERROR("failed to attach bridge to encoder %s: %d\n",
> > > > +			  encoder->name, ret);
> > > >   #endif
> > > > -
> > > > +	}
> > > 
> > > This looks fine as such, but I'm concerned about the direction it's
> > > taking. Ideally, probe deferral should happen at probe time, way before
> > > the bridge is attached. Doing otherwise is a step in the wrong direction
> > > in my opinion, and something we'll end up regretting when we'll feel the
> > > pain it inflicts.
> > 
> > The particular case I'm seeing this is the nwl driver probe deferrals if
> > the panel bridge isn't ready (which needs a bunch of components
> > (dsi, panel, backlight wrapped led, ...) and it probes fine later on so I
> > wonder where you see the actual error cause? That downstream of the
> > bridge isn't ready or that the display controller is already attaching
> > the bridge?
> 
> So it is something wrong there, nwl should not publish bridge interface
> until it gather its resources (the panel in this case).

That helps, I'll look at that. Thanks!
 -- Guido

> 
> Regards
> Andrzej
> 
> 
> > 
> > Cheers,
> >   -- Guido
> > 
> > > 
> > > >   	return ret;
> > > >   }
> > > >   EXPORT_SYMBOL(drm_bridge_attach);
> > > 
> > > -- 
> > > Regards,
> > > 
> > > Laurent Pinchart
> > > 
>