Re: [PATCH 6/8] i3c: master: Defer new-device registration out of DAA caller context

[Adrian Hunter]

On 12/05/2026 19:39, Frank Li wrote:
> On Tue, May 12, 2026 at 03:17:30PM +0300, Adrian Hunter wrote:
>> Master drivers may invoke i3c_master_do_daa_ext() during resume to
>> re-run Dynamic Address Assignment.  As well as assigning addresses to
>> any newly arrived devices, this restores the dynamic address of devices
>> that lost it across system suspend, so it has to run as part of the
>> controller's resume path.
>>
>> A side effect of i3c_master_do_daa_ext() today is that it also
>> registers any newly discovered I3C devices with the driver model
>> inline, via i3c_master_register_new_i3c_devs().  Doing that from the
>> resume path is problematic: a hot-join-capable device may join the bus
>> during this same DAA, and registering it immediately would push driver
>> model work (probing, sysfs, etc.) into the controller's resume context,
>> where the rest of the system is not yet fully resumed and the
>> controller driver is still partway through its own resume sequence.
>>
>> Decouple discovery from registration: add a reg_work work item to
>> struct i3c_master_controller and have i3c_master_do_daa_ext() queue it
>> on master->wq (the freezable workqueue) instead of calling
>> i3c_master_register_new_i3c_devs() directly.  The worker performs the
>> registration only when the controller is not shutting_down, and is
>> cancelled alongside hj_work in i3c_master_shutdown().  Because wq is
>> freezable, any newly observed devices end up being registered after
>> the system has finished resuming.
>>
>> i3c_master_register() also routes its initial post-bus-init registration
>> through reg_work, using flush_work() to keep probe-time behavior
>> synchronous.  This keeps a single registration code path and ensures the
>> worker is the only writer of desc->dev.
> 
> why not direct use hj_work?

i3c_master_register_new_i3c_devs() use of desc->dev is racy, so
i3c_master_register_new_i3c_devs() must not be allowed to race
with itself.  Having it only ever run via reg_work achieves that.