[PATCH v2] i3c: master: Add sysfs option to rescan bus.

[Frank Li]

On Thu, Jan 22, 2026 at 06:08:29PM +0000, Joshua Yeong wrote:
> On Friday, January 23, 2026 1:58 AM, David Nyström wrote:
>
> > Add the ability to rescan the i3c bus from userspace, i.e. provoke a DDA.
> > The usecase could be f.ex. an i3cdev userspace driver for a device with broken hotjoin support. If the i3c device boots slowly, it might be miss the DDA during boot.
> >
> > Signed-off-by: David Nyström <david.nystrom at est.tech>
> > ---
>
> Can we rename rescan to something where indicate we are only doing ENTDAA? I think rescan keyword should be reserved for complete rescan of i3c bus.
> DISEC -> RSTDAA -> ENTDAA -> ...

Look like this is more userful. The only do_daa() is not enough for rescan.

Frank
>
> > Changes in v2:
> > - Improved the commit message with "why".
> > - Link to v1: https://patch.msgid.link/20260122-i3c_rescan-v1-1-0c17071e232b@est.tech
> > ---
> >  drivers/i3c/master.c | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> >
> > diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c index 80dda0e85558..edeae7493b3b 100644
> > --- a/drivers/i3c/master.c
> > +++ b/drivers/i3c/master.c
> > @@ -758,6 +758,29 @@ static ssize_t dev_nack_retry_count_store(struct device *dev,
> >
> >  static DEVICE_ATTR_RW(dev_nack_retry_count);
> >
> > +static ssize_t rescan_store(struct device *dev,
> > +			    struct device_attribute *attr,
> > +			    const char *buf, size_t count)
> > +{
> > +	struct i3c_master_controller *master = dev_to_i3cmaster(dev);
> > +	unsigned long val;
> > +	int ret;
> > +
> > +	ret = kstrtoul(buf, 0, &val);
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (val) {
> > +		ret = i3c_master_do_daa(master);
> > +		if (ret)
> > +			return ret;
> > +	}
> > +
> > +	return count;
> > +}
> > +
> > +static DEVICE_ATTR_WO(rescan);
> > +
> >  static struct attribute *i3c_masterdev_attrs[] = {
> >  	&dev_attr_mode.attr,
> >  	&dev_attr_current_master.attr,
> > @@ -769,6 +792,7 @@ static struct attribute *i3c_masterdev_attrs[] = {
> >  	&dev_attr_dynamic_address.attr,
> >  	&dev_attr_hdrcap.attr,
> >  	&dev_attr_hotjoin.attr,
> > +	&dev_attr_rescan.attr,
> >  	NULL,
> >  };
> >  ATTRIBUTE_GROUPS(i3c_masterdev);
> >
> > ---
> > base-commit: e3b32dcb9f23e3c3927ef3eec6a5842a988fb574
> > change-id: 20260116-i3c_rescan-4921d0b41a00
> >
> > Best regards,
> > --
> > David Nyström <david.nystrom at est.tech>
> >
> >
> > --
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> > linux-i3c at lists.infradead.org
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