Re: [PATCH v6] i3c: master: Add sysfs option to rescan bus via entdaa

[Meagan Lloyd <meaganlloyd@linux.microsoft.com>]

On Fri, Feb 20, 2026 at 11:05:26AM -0500, Frank Li wrote:
> On Thu, Feb 19, 2026 at 09:58:03PM +0100, David Nyström wrote:
> > Allow userspace to request dynamic address assignment, which is
> > useful for i3cdev devices with broken hot-join support.
> > This will assign dynamic addresses to all devices on the I3C bus
> > which are currently unassigned.
> >
> > Signed-off-by: David Nyström <david.nystrom@est.tech>
> > ---
> Reviewed-by: Frank Li <Frank.Li@nxp.com>

Reviewed-by: Meagan Lloyd <meaganlloyd@linux.microsoft.com>

> > Changes in v6:
> > - Add check for init_done to close race with init.
> > - Link to v5: https://patch.msgid.link/20260219-i3c_rescan-v5-1-42404db20d18@est.tech
> >
> > Changes in v5:
> > - Change sysfs interface to boolean. Comment: Meagan Lloyd
> > - Change sysfs entry name to do_daa: Comment Megan Lloyd, Frank Li
> > - Link to v4: https://patch.msgid.link/20260126-i3c_rescan-v4-1-6b3559d82abc@est.tech
> >
> > Changes in v4:
> > - Improved commit message, once more. Comment: Frank Li
> > - Added required documentation for sysfs addition. Comment: Frank Li
> > - Link to v3: https://patch.msgid.link/20260123-i3c_rescan-v3-1-026429fa0c65@est.tech
> >
> > Changes in v3:
> > - Rename sysfs entry from rescan to entdda, Comment: Joshua Yeong
> > - Link to v2: https://patch.msgid.link/20260122-i3c_rescan-v2-1-84c74a483f03@est.tech
> >
> > Changes in v2:
> > - Improved the commit message with why.
> > - Link to v1: https://patch.msgid.link/20260122-i3c_rescan-v1-1-0c17071e232b@est.tech
> > ---
> >  Documentation/ABI/testing/sysfs-bus-i3c | 20 ++++++++++++++++++++
> >  drivers/i3c/master.c                    | 27 +++++++++++++++++++++++++++
> >  2 files changed, 47 insertions(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-i3c b/Documentation/ABI/testing/sysfs-bus-i3c
> > index c1e048957a01..19f5cf8b1b11 100644
> > --- a/Documentation/ABI/testing/sysfs-bus-i3c
> > +++ b/Documentation/ABI/testing/sysfs-bus-i3c
> > @@ -172,3 +172,23 @@ Description:
> >  		the automatic retries. Exist only when I3C constroller supports
> >  		this retry on nack feature.
> >
> > +What:		/sys/bus/i3c/devices/i3c-<bus-id>/do_daa
> > +KernelVersion:  7.0
> > +Contact:	linux-i3c@vger.kernel.org
> > +Description:
> > +		Write-only attribute that triggers a Dynamic Address Assignment
> > +		(DAA) procedure which discovers new I3C devices on the bus.
> > +		Writing a boolean true value (1, y, yes, true, on) to this
> > +		attribute causes the master controller to perform DAA, which
> > +		includes broadcasting an ENTDAA (Enter Dynamic Address Assignment)
> > +		Common Command Code (CCC) on the bus. Writing a false value
> > +		returns -EINVAL.
> > +
> > +		This is useful for discovering I3C devices that were not present
> > +		during initial bus initialization and are unable to issue
> > +		Hot-Join. Only devices without a currently assigned dynamic address
> > +		will respond to the ENTDAA broadcast and be assigned addresses.
> > +
> > +		Note that this mechanism is distinct from Hot-Join, since this is
> > +		controller-initiated discovery, while Hot-Join is device-initiated
> > +		method to provoke controller discovery procedure.
> > diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> > index 0eae19b3823d..8f49d4ad473d 100644
> > --- a/drivers/i3c/master.c
> > +++ b/drivers/i3c/master.c
> > @@ -758,6 +758,32 @@ static ssize_t dev_nack_retry_count_store(struct device *dev,
> >
> >  static DEVICE_ATTR_RW(dev_nack_retry_count);
> >
> > +static ssize_t do_daa_store(struct device *dev,
> > +			    struct device_attribute *attr,
> > +			    const char *buf, size_t count)
> > +{
> > +	struct i3c_master_controller *master = dev_to_i3cmaster(dev);
> > +	bool val;
> > +	int ret;
> > +
> > +	if (kstrtobool(buf, &val))
> > +		return -EINVAL;
> > +
> > +	if (!val)
> > +		return -EINVAL;
> > +
> > +	if (!master->init_done)
> > +		return -EAGAIN;
> > +
> > +	ret = i3c_master_do_daa(master);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return count;
> > +}
> > +
> > +static DEVICE_ATTR_WO(do_daa);
> > +
> >  static struct attribute *i3c_masterdev_attrs[] = {
> >  	&dev_attr_mode.attr,
> >  	&dev_attr_current_master.attr,
> > @@ -769,6 +795,7 @@ static struct attribute *i3c_masterdev_attrs[] = {
> >  	&dev_attr_dynamic_address.attr,
> >  	&dev_attr_hdrcap.attr,
> >  	&dev_attr_hotjoin.attr,
> > +	&dev_attr_do_daa.attr,
> >  	NULL,
> >  };
> >  ATTRIBUTE_GROUPS(i3c_masterdev);
> >
> > ---
> > base-commit: 44982d352c33767cd8d19f8044e7e1161a587ff7
> > change-id: 20260116-i3c_rescan-4921d0b41a00
> >
> > Best regards,
> > --
> > David Nyström <david.nystrom@est.tech>
> >