Re: [PATCH] drm/vc4: dsi: Only register our component once a DSI device is attached

[Eric Anholt]

On Tue, Jul 7, 2020 at 3:26 AM Maxime Ripard <maxime@xxxxxxxxxx> wrote:
>
> If the DSI driver is the last to probe, component_add will try to run all
> the bind callbacks straight away and return the error code.
>
> However, since we depend on a power domain, we're pretty much guaranteed to
> be in that case on the BCM2711, and are just lucky on the previous SoCs
> since the v3d also depends on that power domain and is further in the probe
> order.
>
> In that case, the DSI host will not stick around in the system: the DSI
> bind callback will be executed, will not find any DSI device attached and
> will return EPROBE_DEFER, and we will then remove the DSI host and ask to
> be probed later on.
>
> But since that host doesn't stick around, DSI devices like the RaspberryPi
> touchscreen whose probe is not linked to the DSI host (unlike the usual DSI
> devices that will be probed through the call to mipi_dsi_host_register)
> cannot attach to the DSI host, and we thus end up in a situation where the
> DSI host cannot probe because the panel hasn't probed yet, and the panel
> cannot probe because the DSI host hasn't yet.
>
> In order to break this cycle, let's wait until there's a DSI device that
> attaches to the DSI host to register the component and allow to progress
> further.
>
> Suggested-by: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> Signed-off-by: Maxime Ripard <maxime@xxxxxxxxxx>

I feel like I've written this patch before, but I've thankfully
forgotten most of my battle with DSI probing.  As long as this still
lets vc4 probe in the absence of a DSI panel in the DT as well, then
this is enthusiastically acked.