[PATCH] i3c: master: Add WO sysfs option to re-DDA bus.

[PATCH] i3c: master: Add WO sysfs option to re-DDA bus.

[David Nyström]

Add ability to rescan the i3c bus from userspace, i.e. provoke a DDA.

Signed-off-by: David Nyström <david.nystrom@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: 9b7977f9e39b7768c70c2aa497f04e7569fd3e00
change-id: 20260116-i3c_rescan-4921d0b41a00

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


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Re: [PATCH] i3c: master: Add WO sysfs option to re-DDA bus.

[Wolfram Sang]

On Thu, Jan 22, 2026 at 12:36:30PM +0100, David Nyström wrote:
> Add ability to rescan the i3c bus from userspace, i.e. provoke a DDA.

Your are describing what you do but what is missing is why you want the
change. What is the use case?


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Re: [PATCH] i3c: master: Add WO sysfs option to re-DDA bus.

[David Nyström]

[-- Attachment #1: Type: text/plain, Size: 851 bytes --]


On Thu, 22 Jan 2026, Wolfram Sang wrote:

> On Thu, Jan 22, 2026 at 12:36:30PM +0100, David Nyström wrote:
>> Add ability to rescan the i3c bus from userspace, i.e. provoke a DDA.
>
> Your are describing what you do but what is missing is why you want the
> change. What is the use case?

The usecase would be an i3cdev userspace driver for a device with 
broken hotjoin support.
The device requires FW loading(userspace framework) before it will respond 
to DAA, and is thus not registered during initial bus probe.
I guess a similiar problem would apply if hot-join is bus disabled 
via sysfs, and resume hook DDA runs before i3c devices are powered up properly.

A bit of a niche usecase, I know.
I found it to be usable though, but perhaps this is better placed in 
debugfs in case its too much of an eyesore for the stable ABI.

[-- Attachment #2: Type: text/plain, Size: 111 bytes --]

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Re: [PATCH] i3c: master: Add WO sysfs option to re-DDA bus.

[Frank Li]

On Thu, Jan 22, 2026 at 04:47:23PM +0100, David Nyström wrote:
>
> On Thu, 22 Jan 2026, Wolfram Sang wrote:
>
> > On Thu, Jan 22, 2026 at 12:36:30PM +0100, David Nyström wrote:
> > > Add ability to rescan the i3c bus from userspace, i.e. provoke a DDA.
> >
> > Your are describing what you do but what is missing is why you want the
> > change. What is the use case?
>
> The usecase would be an i3cdev userspace driver for a device with broken
> hotjoin support.
> The device requires FW loading(userspace framework) before it will respond
> to DAA, and is thus not registered during initial bus probe.
> I guess a similiar problem would apply if hot-join is bus disabled via
> sysfs, and resume hook DDA runs before i3c devices are powered up properly.
>
> A bit of a niche usecase, I know.
> I found it to be usable though, but perhaps this is better placed in debugfs
> in case its too much of an eyesore for the stable ABI.

It is useful. Please improve commit message.

Frank


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