linux-kernel - Re: [PATCH 04/10] drm/bridge: Document the probe issue with MIPI-DSI bridges

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Date:   Tue, 27 Jul 2021 11:20:54 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Robert Foss <robert.foss@...aro.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Sam Ravnborg <sam@...nborg.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 04/10] drm/bridge: Document the probe issue with MIPI-DSI
 bridges

On Mon, Jul 26, 2021 at 05:16:57PM +0200, Maxime Ripard wrote:
> Hi Daniel,
> 
> On Wed, Jul 21, 2021 at 02:05:01PM +0200, Daniel Vetter wrote:
> > On Tue, Jul 20, 2021 at 03:45:19PM +0200, Maxime Ripard wrote:
> > > Interactions between bridges, panels, MIPI-DSI host and the component
> > > framework are not trivial and can lead to probing issues when
> > > implementing a display driver. Let's document the various cases we need
> > > too consider, and the solution to support all the cases.
> > > 
> > > Signed-off-by: Maxime Ripard <maxime@...no.tech>
> > 
> > I still have this dream that eventually we resurrect a patch to add
> > device_link to bridges/panels (ideally automatically), to help with some
> > of the suspend/resume issues around here.
> > 
> > Will this make things worse?
> > 
> > I think it'd be really good to figure that out with some coding, since if
> > we have incompatible solution to handle probe issues vs suspend/resume
> > issues, we're screwed.
> > 
> > Atm the duct-tape is to carefully move things around between suspend and
> > suspend_early hooks (and resume and resume_late) and hope it all works ...
> 
> My initial idea to fix this was indeed to use device links. I gave up
> after a while since it doesn't look like there's a way to add a device
> link before either the bridge or encoder probes.
> 
> Indeed the OF-Graph representation is device-specific, so it can't be
> generic, and if you need to probe to add that link, well, it's already
> too late for the probe ordering :)

But don't we still need the device_link for suspend/resume and module
reload? All very annoying indeed anyway.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch