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authorRob Herring <robh@kernel.org>2018-07-09 18:41:48 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-07-10 18:22:35 +0300
commit25b4e70dcce92168eab4d8113817bb4dd130ebd2 (patch)
treeeb08ff1080319008d0e75df75f7fbc1c1b5848fc /Documentation/admin-guide
parent28af109a57d14211e5e8ba1551f00428be2fd508 (diff)
downloadlinux-25b4e70dcce92168eab4d8113817bb4dd130ebd2.tar.xz
driver core: allow stopping deferred probe after init
Deferred probe will currently wait forever on dependent devices to probe, but sometimes a driver will never exist. It's also not always critical for a driver to exist. Platforms can rely on default configuration from the bootloader or reset defaults for things such as pinctrl and power domains. This is often the case with initial platform support until various drivers get enabled. There's at least 2 scenarios where deferred probe can render a platform broken. Both involve using a DT which has more devices and dependencies than the kernel supports. The 1st case is a driver may be disabled in the kernel config. The 2nd case is the kernel version may simply not have the dependent driver. This can happen if using a newer DT (provided by firmware perhaps) with a stable kernel version. Deferred probe issues can be difficult to debug especially if the console has dependencies or userspace fails to boot to a shell. There are also cases like IOMMUs where only built-in drivers are supported, so deferring probe after initcalls is not needed. The IOMMU subsystem implemented its own mechanism to handle this using OF_DECLARE linker sections. This commit adds makes ending deferred probe conditional on initcalls being completed or a debug timeout. Subsystems or drivers may opt-in by calling driver_deferred_probe_check_init_done() instead of unconditionally returning -EPROBE_DEFER. They may use additional information from DT or kernel's config to decide whether to continue to defer probe or not. The timeout mechanism is intended for debug purposes and WARNs loudly. The remaining deferred probe pending list will also be dumped after the timeout. Not that this timeout won't work for the console which needs to be enabled before userspace starts. However, if the console's dependencies are resolved, then the kernel log will be printed (as opposed to no output). Cc: Alexander Graf <agraf@suse.de> Signed-off-by: Rob Herring <robh@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt9
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index efc7aa7a0670..e83ef4648ea4 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -804,6 +804,15 @@
Defaults to the default architecture's huge page size
if not specified.
+ 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. This option will also
+ dump out devices still on the deferred probe list after
+ retrying.
+
dhash_entries= [KNL]
Set number of hash buckets for dentry cache.