Re: [PATCH v2 resend] driver core: Make deferred_probe_timeout default a Kconfig option

[Hans de Goede]

Hi Danilo,

On 30-Mar-26 21:13, Danilo Krummrich wrote:
> On Sat Mar 14, 2026 at 9:49 AM CET, Hans de Goede wrote:
>> Code using driver_deferred_probe_check_state() differs from most
>> EPROBE_DEFER handling in the kernel. Where other EPROBE_DEFER handling
>> (e.g. clks, gpios and regulators) waits indefinitely for suppliers to
>> show up, code using driver_deferred_probe_check_state() will fail
>> after the deferred_probe_timeout.
>>
>> This is a problem for generic distro kernels which want to support many
>> boards using a single kernel build. These kernels want as much drivers to
>> be modular as possible. The initrd also should be as small as possible,
>> so the initrd will *not* have drivers not needing to get the rootfs.
>>
>> Combine this with waiting for a full-disk encryption password in
>> the initrd and it is pretty much guaranteed that the default 10s timeout
>> will be hit, causing probe() failures when drivers on the rootfs happen
>> to get modprobe-d before other rootfs modules providing their suppliers.
>>
>> Make the default timeout configurable from Kconfig to allow distro kernel
>> configs where many of the supplier drivers are modules to set the default
>> through Kconfig.
>>
>> While at it document that a value of -1 can be used to disable the timeout
>> (wait indefinitely).
>>
>> Acked-by: Saravana Kannan <saravanak@xxxxxxxxxx>
>> Signed-off-by: Hans de Goede <johannes.goede@xxxxxxxxxxxxxxxx>
> 
> Applied to driver-core-testing, thanks!
> 
>     [ Drop deferred_probe_timeout documentation change in
>       kernel-parameters.txt. - Danilo ]

Thank you!

> Sorry for the delay

No problem, as you see from my reply speed I've been busy
with other things myself too.

> I dropped the documentation change as I think it deserves
> a separate patch and I think that just adding "Set to -1 to wait indefinitely."
> at the end doesn't read very well.

Ok, I'll submit a separate patch for this soon.

> (Also, I think every negative value will result in waiting indefinitely.)
> 
> I also upgraded Saravana's ACK (which already was conditional on this change
> before) to an RB, as offered in [1].

Ack.

> 	deferred_probe_timeout=
> 		[KNL] Debugging option to set a timeout in seconds for
> 		deferred probe to give up waiting on dependencies to
> 		probe. Only specific dependencies (subsystems or
> 		drivers) that have opted in will be ignored. A timeout
> 		of 0 will timeout at the end of initcalls. If the time
> 		out hasn't expired, it'll be restarted by each
> 		successful driver registration. This option will also
> 		dump out devices still on the deferred probe list after
> 		retrying. Set to -1 to wait indefinitely.
> 
> Maybe something like this?
> 
> 	deferred_probe_timeout=
> 		[KNL] Debugging option to set a timeout in seconds for
> 		deferred probe to give up waiting on dependencies to
> 		probe. Only specific dependencies (subsystems or
> 		drivers) that have opted in will be ignored. A timeout
> 		of 0 will timeout at the end of initcalls; a negative value
> 		is treated as an infinite timeout value. If the timeout
> 		hasn't expired, it'll be restarted by each successful
> 		driver registration. This option will also dump out devices
> 		still on the deferred probe list after retrying.

Sounds good, I'll send a patch with the suggested text.

Regards,

Hans