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

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Message-ID: <20260204150045.32892-1-johannes.goede@oss.qualcomm.com>
Date: Wed,  4 Feb 2026 16:00:45 +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: Hans de Goede <johannes.goede@....qualcomm.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] driver core: Make deferred_probe_timeout default a Kconfig option

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.
-- 
2.52.0