From: Vincent Jardin <vjardin@free.fr>

Unbinding and re-binding the root DPRC fails with:

  sysfs: cannot create duplicate filename '/dev/char/10:256'
    misc_register / fsl_mc_uapi_create_device_file /
    dprc_setup / dprc_probe

It happens when the fsl-mc bus probe is not deferred, without SMMU:
- the dprc driver is registered at postcore_initcall,
- the DT node is populated at arch_initcall_sync,
- the root DPRC probes right there, before misc_init() has
  registered misc_class at subsys_initcall.

misc_register() still succeeds but the device gets
no class, so misc_deregister() at unbind cannot find it:
the minor is freed while the device and its /sys/dev/char/ link leak,
and then the next bind collides on the same minor.

Let's move the dprc and allocator drivers registration, and
platform_driver_register(), to subsys_initcall_sync, after misc_init()
at subsys_initcall.
bus_register() and the platform-bus notifier stay at postcore_initcall
so that fsl_mc_bus_notifier() still pauses the MC before the SMMU is probed.

Cc: stable+noautosel@kernel.org # niche: root DPRC unbind/rebind only
Fixes: 2cf1e703f066 ("bus: fsl-mc: add fsl-mc userspace support")
Signed-off-by: Vincent Jardin <vjardin@free.fr>
---
Issue found when unbinding/rebinding the root DPRC on an LX2160A.

The failure is silent at bind time and only shows up as a
duplicate /dev/char entry on the second bind.
---
Changes in v2:
- Commit message: the bug needs a non-deferred fsl-mc bus
  probe (no SMMU) - Ioana Ciornei
- No code change
- Link to v1: https://lore.kernel.org/r/20260901-for-upstream-fsl-mc-initcall-order-v1-1-36ffe48f767d@free.fr
---
 drivers/bus/fsl-mc/fsl-mc-bus.c | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bus.c
index 66a4fa73c5b86..7f283844e4500 100644
--- a/drivers/bus/fsl-mc/fsl-mc-bus.c
+++ b/drivers/bus/fsl-mc/fsl-mc-bus.c
@@ -1264,35 +1264,43 @@ static int __init fsl_mc_bus_driver_init(void)
 	error = bus_register(&fsl_mc_bus_type);
 	if (error < 0) {
 		pr_err("bus type registration failed: %d\n", error);
-		goto error_cleanup_cache;
+		return error;
 	}
 
-	error = platform_driver_register(&fsl_mc_bus_driver);
-	if (error < 0) {
-		pr_err("platform_driver_register() failed: %d\n", error);
+	error = bus_register_notifier(&platform_bus_type, &fsl_mc_nb);
+	if (error < 0)
 		goto error_cleanup_bus;
-	}
+
+	return 0;
+
+error_cleanup_bus:
+	bus_unregister(&fsl_mc_bus_type);
+	return error;
+}
+postcore_initcall(fsl_mc_bus_driver_init);
+
+static int __init fsl_mc_bus_drivers_init(void)
+{
+	int error;
 
 	error = dprc_driver_init();
 	if (error < 0)
-		goto error_cleanup_driver;
+		return error;
 
 	error = fsl_mc_allocator_driver_init();
 	if (error < 0)
 		goto error_cleanup_dprc_driver;
 
-	return bus_register_notifier(&platform_bus_type, &fsl_mc_nb);
+	error = platform_driver_register(&fsl_mc_bus_driver);
+	if (error < 0) {
+		pr_err("platform_driver_register() failed: %d\n", error);
+		goto error_cleanup_dprc_driver;
+	}
+
+	return 0;
 
 error_cleanup_dprc_driver:
 	dprc_driver_exit();
-
-error_cleanup_driver:
-	platform_driver_unregister(&fsl_mc_bus_driver);
-
-error_cleanup_bus:
-	bus_unregister(&fsl_mc_bus_type);
-
-error_cleanup_cache:
 	return error;
 }
-postcore_initcall(fsl_mc_bus_driver_init);
+subsys_initcall_sync(fsl_mc_bus_drivers_init);

---
base-commit: 786262be6048deab760f68c8acc2c85607165894
change-id: 20260922-for-upstream-fsl-mc-initcall-order-e3316390712b

Best regards,
-- 
Vincent Jardin <vjardin@free.fr>

On Wed, 09 Sep 2026 19:04:40 +0200, Vincent Jardin wrote:
> Unbinding and re-binding the root DPRC fails with:
> 
>   sysfs: cannot create duplicate filename '/dev/char/10:256'
>     misc_register / fsl_mc_uapi_create_device_file /
>     dprc_setup / dprc_probe
> 
> It happens when the fsl-mc bus probe is not deferred, without SMMU:
> - the dprc driver is registered at postcore_initcall,
> - the DT node is populated at arch_initcall_sync,
> - the root DPRC probes right there, before misc_init() has
>   registered misc_class at subsys_initcall.
> 
> [...]

Applied, thanks!

[1/1] bus: fsl-mc: register the object drivers after misc_class exists
      commit: 7e9023a18eec88b716d8d46a29c4207186fbd828

Best regards,
-- 
Christophe Leroy (CS GROUP) <chleroy@kernel.org>

On Wed, Sep 09, 2026 at 07:04:40PM +0200, Vincent Jardin via B4 Relay wrote:
> From: Vincent Jardin <vjardin@free.fr>
> 
> Unbinding and re-binding the root DPRC fails with:
> 
>   sysfs: cannot create duplicate filename '/dev/char/10:256'
>     misc_register / fsl_mc_uapi_create_device_file /
>     dprc_setup / dprc_probe
> 
> It happens when the fsl-mc bus probe is not deferred, without SMMU:
> - the dprc driver is registered at postcore_initcall,
> - the DT node is populated at arch_initcall_sync,
> - the root DPRC probes right there, before misc_init() has
>   registered misc_class at subsys_initcall.
> 
> misc_register() still succeeds but the device gets
> no class, so misc_deregister() at unbind cannot find it:
> the minor is freed while the device and its /sys/dev/char/ link leak,
> and then the next bind collides on the same minor.
> 
> Let's move the dprc and allocator drivers registration, and
> platform_driver_register(), to subsys_initcall_sync, after misc_init()
> at subsys_initcall.
> bus_register() and the platform-bus notifier stay at postcore_initcall
> so that fsl_mc_bus_notifier() still pauses the MC before the SMMU is probed.
> 

Thank you for the updated commit message.

> Cc: stable+noautosel@kernel.org # niche: root DPRC unbind/rebind only
> Fixes: 2cf1e703f066 ("bus: fsl-mc: add fsl-mc userspace support")
> Signed-off-by: Vincent Jardin <vjardin@free.fr>

Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>