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

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Message-Id: <20260122-i3c_rescan-v2-1-84c74a483f03@est.tech>
Date: Thu, 22 Jan 2026 18:58:55 +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, 
 David Nyström <david.nystrom@....tech>
Subject: [PATCH v2] i3c: master: Add sysfs option to rescan bus.

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@....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
---
 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@....tech>