Re: [PATCH v4] i3c: master: Add sysfs option to rescan bus via entdaa

[Meagan Lloyd]

On 1/26/2026 9:18 AM, Frank Li wrote:
> On Mon, Jan 26, 2026 at 09:37:01AM +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.
> Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
>> Signed-off-by: David Nyström <david.nystrom@xxxxxxxx>
>> ---
>> 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@xxxxxxxx
>>
>> 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@xxxxxxxx
>>
>> Changes in v2:
>> - Improved the commit message with "why".
>> - Link to v1: https://patch.msgid.link/20260122-i3c_rescan-v1-1-0c17071e232b@xxxxxxxx
>> ---
>>  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@xxxxxxxxxxxxxxx
>> +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;
>> +	}
>> +

Why not use kstrtobool and return -EINVAL for inputs that evaluate to false?

>> +	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,
Is 'entdaa' the best naming here? Keeping it general i.e. 'daa' or 'trigger_daa' would be more flexible/extensible in my opinion.
>>  	NULL,
>>  };
>>  ATTRIBUTE_GROUPS(i3c_masterdev);
>>
>> ---
>> base-commit: e3b32dcb9f23e3c3927ef3eec6a5842a988fb574
>> change-id: 20260116-i3c_rescan-4921d0b41a00
>>
>> Best regards,
>> --
>> David Nyström <david.nystrom@xxxxxxxx>
>>
>>
>> --
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