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

[Frank Li <Frank.li@nxp.com>]

On Fri, May 15, 2026 at 07:42:20PM +0300, Adrian Hunter wrote:
> 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

i3c_bus_normaluse_lock() may is wrong, suppose it should be
i3c_bus_maintenance_lock(), register new devices change i3c bus's
hierarchical structure.

Frank

> 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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