On 26/06/2024 18:07, Maxime Ripard wrote:
On Wed, Jun 26, 2024 at 12:55:39PM GMT, Tomi Valkeinen wrote:
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.
I'm not sure what you mean by the attach/detach case. Do you expect
device resources allocated in attach to be freed when detach run?
Ah, never mind, the devres_release_all() would of course deal with that too.
However, I just realized/remembered why it crashes.
devm_mipi_dsi_device_register_full() and devm_mipi_dsi_attach() are
given a device which is used for the devres. This device is probably
always the bridge device. So when the bridge device goes away, so do
those resources.
The mipi_dsi_device_unregister() call deals with a DSI device, which was
created in devm_mipi_dsi_device_register_full(). Unregistering that DSI
device, which does happen when the DSI host is removed, does not affect
the devres of the bridge.
So, unloading the DSI host driver causes mipi_dsi_device_unregister()
and mipi_dsi_detach() to be called (as part of
mipi_dsi_host_unregister()), and unloading the bridge driver causes them
to be called again via devres.
Tomi
