Re: [PATCH] drm/mipi-dsi: Fix devm unregister & detach

[Tomi Valkeinen]

On 26/06/2024 11:49, Maxime Ripard wrote:
> Hi,
>
> On Wed, Jun 19, 2024 at 12:07:48PM GMT, Tomi Valkeinen wrote:
> > From: Tomi Valkeinen <tomi.valkeinen+renesas@xxxxxxxxxxxxxxxx>
> >
> > When a bridge driver uses devm_mipi_dsi_device_register_full() or
> > devm_mipi_dsi_attach(), the resource management is moved to devres,
> > which releases the resource automatically when the bridge driver is
> > unbound.
> >
> > However, if the DSI host goes away first, the host unregistration code
> > will automatically detach and unregister any DSI peripherals, without
> > notifying the devres about it. So when the bridge driver later is
> > unbound, the resources are released a second time, leading to crash.
>
> That's super surprising. mipi_dsi_device_unregister calls
> device_unregister, which calls device_del, which in turn calls
> devres_release_all.

Hmm, right.

> If that doesn't work like that, then it's what needs to be fixed, and
> not worked around in the MIPI-DSI bus.

Well, something causes a crash for both the device register/unregister 
case and the attach/detach case, and the call stacks and debug prints 
showed a double unregister/detach...

I need to dig up the board and check again why the devres_release_all() 
in device_del() doesn't solve this. But I can probably only get back to 
this in August, so it's perhaps best to ignore this patch for now.

However, the attach/detach case is still valid? I see no devres calls in 
the detach paths.

 Tomi