Re: [PATCH] drm/bridge: Ignore -EPROBE_DEFER when bridge attach fails

["Guido Günther" <agx@sigxcpu.org>]

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@0/bus@30800000/mipi-dsi@30a0 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@sigxcpu.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?

Cheers,
 -- Guido

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