Re: [PATCH v2 2/8] driver core: add a deferred probe timeout

On Thu, May 24, 2018 at 12:50:18PM -0500, Rob Herring wrote:

Deferring probe can wait forever on dependencies that may never appear for a variety of reasons. This can be difficult to debug especially if the console has dependencies or userspace fails to boot to a shell. Add a timeout to retry probing without possibly optional dependencies and to dump out the deferred probe pending list after retrying.

This mechanism is intended for debug purposes. It 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).

Signed-off-by: Rob Herring robh@kernel.org

.../admin-guide/kernel-parameters.txt | 7 +++++ drivers/base/dd.c | 28 ++++++++++++++++++- 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 11fc28ecdb6d..dd3f40b34a24 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -809,6 +809,13 @@ Defaults to the default architecture's huge page size if not specified.

• deferred_probe_timeout=

• 	[KNL] 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. This option also dumps out devices
  

• 	still on the deferred probe list after retrying.
  

Doesn't sound like a debugging-only option. I can see devices enabling this when they figure out that's the only way their platform can boot :)

thanks,

greg k-h