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From: "a.hajda" <>
To: Maxime Ripard <>,
	Sam Ravnborg <>,
	Daniel Vetter <>,
	David Airlie <>,
	Thierry Reding <>,
	Laurent Pinchart <>,
	Maarten Lankhorst <>,
	Thomas Zimmermann <>,
	Jernej Skrabec <>,
	Neil Armstrong <>,
	Jonas Karlman <>,
	Robert Foss <>
Subject: Re: [PATCH v2 0/8] drm/bridge: Make panel and bridge probe order consistent
Date: Wed, 4 Aug 2021 16:09:38 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Hi Maxime,

I have been busy with other tasks, and I did not follow the list last 
time, so sorry for my late response.

On 28.07.2021 15:32, Maxime Ripard wrote:
> Hi,
> We've encountered an issue with the RaspberryPi DSI panel that prevented the
> whole display driver from probing.
> The issue is described in detail in the commit 7213246a803f ("drm/vc4: dsi:
> Only register our component once a DSI device is attached"), but the basic idea
> is that since the panel is probed through i2c, there's no synchronization
> between its probe and the registration of the MIPI-DSI host it's attached to.
> We initially moved the component framework registration to the MIPI-DSI Host
> attach hook to make sure we register our component only when we have a DSI
> device attached to our MIPI-DSI host, and then use lookup our DSI device in our
> bind hook.
> However, all the DSI bridges controlled through i2c are only registering their
> associated DSI device in their bridge attach hook, meaning with our change

I guess this is incorrect. I have promoted several times the pattern 
that device driver shouldn't expose its interfaces (for example 
component_add, drm_panel_add, drm_bridge_add) until it gathers all 
required dependencies. In this particular case bridges should defer 
probe until DSI bus becomes available. I guess this way the patch you 
reverts would work.

I advised few times this pattern in case of DSI hosts, apparently I 
didn't notice the similar issue can appear in case of bridges. Or there 
is something I have missed???

Anyway there are already eleven(?) bridge drivers using this pattern. I 
wonder if fixing it would be difficult, or if it expose other issues???
The patches should be quite straightforward - move 
of_find_mipi_dsi_host_by_node and mipi_dsi_device_register_full to probe 

Finally I think that if we will not fix these bridge drivers we will 
encounter another set of issues with new platforms connecting "DSI host 
drivers assuming this pattern" and "i2c/dsi device drivers assuming 
pattern already present in the bridges".


  parent reply	other threads:[~2021-08-04 14:09 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-28 13:32 Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 1/8] Revert "drm/vc4: dsi: Only register our component once a DSI device is attached" Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 2/8] drm/bridge: Add a function to abstract away panels Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 3/8] drm/bridge: Add documentation sections Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 4/8] drm/bridge: Document the probe issue with MIPI-DSI bridges Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 5/8] drm/panel: Create attach and detach callbacks Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 6/8] drm/vc4: dsi: Switch to drm_of_get_bridge Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 7/8] drm/panel: raspberrypi-touchscreen: Use the attach hook Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 8/8] drm/panel: raspberrypi-touchscreen: Remove MIPI-DSI driver Maxime Ripard
     [not found] ` <>
2021-08-04 14:09   ` a.hajda [this message]
2021-08-09  8:00     ` [PATCH v2 0/8] drm/bridge: Make panel and bridge probe order consistent Jagan Teki
2021-08-09 12:03       ` Andrzej Hajda
2021-08-20 16:49     ` Maxime Ripard

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