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

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Message-ID: <20210726151657.c46qmkdvqfhlg6ox@gilmour>
Date:   Mon, 26 Jul 2021 17:16:57 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     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

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 :)

Maxime

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