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

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

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?

Frank
>