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

[Hans de Goede <johannes.goede@oss.qualcomm.com>]

Hi,

On 12-Feb-26 16:22, Saravana Kannan wrote:
> On Thu, Feb 12, 2026 at 6:54 AM Hans de Goede
> <johannes.goede@oss.qualcomm.com> 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@kernel.org>
>> Signed-off-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
>> ---
>> Changes in v2:
>> - Remove unnecessary addition of "if (driver_deferred_probe_timeout < 0)"
>>   check
>> - Add Acked-by from Saravana
>> ---
>>  Documentation/admin-guide/kernel-parameters.txt | 2 +-
>>  drivers/base/Kconfig                            | 9 +++++++++
>>  drivers/base/dd.c                               | 6 +-----
>>  3 files changed, 11 insertions(+), 6 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index aa0031108bc1..d26957741713 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1250,7 +1250,7 @@ Kernel parameters
>>                         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.
>> +                       retrying. Set to -1 to wait indefinitely.
> 
> Forgot to fix this?

As mentioned in the updated commit message:

"While at it document that a value of -1 can be used to disable the timeout
(wait indefinitely)."

I dropped the code-changes for this since -1 is already supported,
it still seems like a good idea to document that -1 can be used
so I decided to keep the documentation change.

Regards,

Hans




 
>>
>>         delayacct       [KNL] Enable per-task delay accounting
>>
>> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
>> index 1786d87b29e2..f7d385cbd3ba 100644
>> --- a/drivers/base/Kconfig
>> +++ b/drivers/base/Kconfig
>> @@ -73,6 +73,15 @@ config DEVTMPFS_SAFE
>>           with the PROT_EXEC flag. This can break, for example, non-KMS
>>           video drivers.
>>
>> +config DRIVER_DEFERRED_PROBE_TIMEOUT
>> +       int "Default value for deferred_probe_timeout"
>> +       default 0 if !MODULES
>> +       default 10 if MODULES
>> +       help
>> +         Set the default value for the deferred_probe_timeout kernel parameter.
>> +         See Documentation/admin-guide/kernel-parameters.txt for a description
>> +         of the deferred_probe_timeout kernel parameter.
>> +
>>  config STANDALONE
>>         bool "Select only drivers that don't need compile-time external firmware"
>>         default y
>> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
>> index bea8da5f8a3a..2f358e29e0e8 100644
>> --- a/drivers/base/dd.c
>> +++ b/drivers/base/dd.c
>> @@ -257,11 +257,7 @@ static int deferred_devs_show(struct seq_file *s, void *data)
>>  }
>>  DEFINE_SHOW_ATTRIBUTE(deferred_devs);
>>
>> -#ifdef CONFIG_MODULES
>> -static int driver_deferred_probe_timeout = 10;
>> -#else
>> -static int driver_deferred_probe_timeout;
>> -#endif
>> +static int driver_deferred_probe_timeout = CONFIG_DRIVER_DEFERRED_PROBE_TIMEOUT;
>>
>>  static int __init deferred_probe_timeout_setup(char *str)
>>  {
>> --
>> 2.52.0
>>