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

[Adrian Hunter <adrian.hunter@intel.com>]

On 13/05/2026 22:03, Frank Li wrote:
> On Wed, May 13, 2026 at 08:45:55AM +0300, Adrian Hunter wrote:
>> 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.
> 
> Sorry, I have not understand these, Can provide some detail?

From i3c_master_register_new_i3c_devs():

	i3c_bus_for_each_i3cdev(&master->bus, desc) {
		if (desc->dev || !desc->info.dyn_addr || desc == master->this)
			continue;

		desc->dev = kzalloc_obj(*desc->dev);
		...
		ret = device_register(&desc->dev->dev);

This is done under the shared i3c_bus_normaluse_lock(), so there can
be 2 or more instances of i3c_master_register_new_i3c_devs() running
at the same time.  They might all see desc->dev is NULL and then all
of them try to initialize and register a dev for the same I3C device.


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