Re: [RFC PATCH v3] drivercore: Add driver probe deferral mechanism

Grant Likely
2011-10-04T15:53:14Z

On Mon, Oct 3, 2011 at 5:02 PM, Kevin Hilman <khilman@ti.com> wrote:
> Grant Likely <grant.likely@secretlab.ca> writes:
>
>> Allow drivers to report at probe time that they cannot get all the resources
>> required by the device, and should be retried at a later time.
>>
>> This should completely solve the problem of getting devices
>> initialized in the right order.  Right now this is mostly handled by
>> mucking about with initcall ordering which is a complete hack, and
>> doesn't even remotely handle the case where device drivers are in
>> modules.  This approach completely sidesteps the issues by allowing
>> driver registration to occur in any order, and any driver can request
>> to be retried after a few more other drivers get probed.
>
> This is great work, thanks!
>
> For the TODO list:
>
> While the proposed patch should solve probe order dependencies, I don't
> think it will solve the suspend/resume ordering dependencies, which are
> typically the same.
>
> Currenly suspend/resume order is based on the order devices are *added*
> (device_add() -> device_pm_add() -> device added to dpm_list), so
> unfortunately, deferring probe isn't going to affect suspend/resume
> ordering.
>
> Extending this to also address suspend/resume ordering by also changing
> when the device is added to the dpm_list (or possibly creating another
> list) should probably be explored as well.

Hmm, yes, I think this is worth exploring. It doesn't help with
runtime pm dependencies, but it has the potential to make PM just work
if the list order is updated each time a device is successfully bound
to a driver. Manjunath, can you investigate what it would take to do
this? (after getting the core deferral patch finalized; I don't want
to block that work)?

g.