linux-kernel - Re: [PATCH] driver core: Make deferred_probe

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Message-ID: <63fa1288-c472-4cdd-ae64-dbb32fc6574f@oss.qualcomm.com>
Date: Thu, 5 Feb 2026 10:14:30 +0100
From: Hans de Goede <johannes.goede@....qualcomm.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Danilo Krummrich <dakr@...nel.org>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] driver core: Make deferred_probe_timeout default a
 Kconfig option

Hi all,

On 4-Feb-26 16:00, 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 and allow using a value of -1 to disable the timeout
> (wait indefinitely).
> 
> Signed-off-by: Hans de Goede <johannes.goede@....qualcomm.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 2 +-
>  drivers/base/Kconfig                            | 9 +++++++++
>  drivers/base/dd.c                               | 9 ++++-----
>  3 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 1058f2a6d6a8..80d300c4e16b 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.
>  
>  	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..e57144aa168d 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)
>  {

> @@ -323,6 +319,9 @@ static DECLARE_DELAYED_WORK(deferred_probe_timeout_work, deferred_probe_timeout_
>  
>  void deferred_probe_extend_timeout(void)
>  {
> +	if (driver_deferred_probe_timeout < 0)
> +		return;
> +
>  	/*
>  	 * If the work hasn't been queued yet or if the work expired, don't
>  	 * start a new one.

I just realized that this last bit adding the < 0 check is not necessary.
The work never gets scheduled if driver_deferred_probe_timeout < 0 so
the existing "if (cancel_delayed_work(&deferred_probe_timeout_work))"
check is enough to not re-schedule in this case.

I'll drop this for v2. Note I'm waiting with sending a v2 for a bit
on case there are more remarks.

Regards,

Hans