linux-kernel - [PATCH v4] i3c: master: Add sysfs option to rescan bus via entdaa

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Message-Id: <20260126-i3c_rescan-v4-1-6b3559d82abc@est.tech>
Date: Mon, 26 Jan 2026 09:37:01 +0100
From: David Nyström <david.nystrom@....tech>
To: Alexandre Belloni <alexandre.belloni@...tlin.com>, 
 Frank Li <Frank.Li@....com>
Cc: linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Joshua Yeong <joshua.yeong@...rfivetech.com>, 
 David Nyström <david.nystrom@....tech>
Subject: [PATCH v4] i3c: master: Add sysfs option to rescan bus via entdaa

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@....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 | 19 +++++++++++++++++++
 drivers/i3c/master.c                    | 24 ++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-i3c b/Documentation/ABI/testing/sysfs-bus-i3c
index c1e048957a01..040824ac7401 100644
--- a/Documentation/ABI/testing/sysfs-bus-i3c
+++ b/Documentation/ABI/testing/sysfs-bus-i3c
@@ -172,3 +172,22 @@ Description:
 		the automatic retries. Exist only when I3C constroller supports
 		this retry on nack feature.
 
+What:		/sys/bus/i3c/devices/i3c-<bus-id>/entdaa
+KernelVersion:  6.20
+Contact:	linux-i3c@...r.kernel.org
+Description:
+		Write-only attribute that triggers a Dynamic Address Assignment
+		(DAA) procedure which discovers new I3C devices on the bus.
+		Writing any non-zero value to this attribute
+		causes the master controller to broadcast an ENTDAA
+		(Enter Dynamic Address Assignment) Common Command Code(CCC) on
+		the bus.
+
+		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 80dda0e85558..a1d816634a25 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 entdaa_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(entdaa);
+
 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_entdaa.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(i3c_masterdev);

---
base-commit: e3b32dcb9f23e3c3927ef3eec6a5842a988fb574
change-id: 20260116-i3c_rescan-4921d0b41a00

Best regards,
--  
David Nyström <david.nystrom@....tech>