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Message-ID: <149b630d-ba89-453d-aad1-a0d96b0c26b6@linux.microsoft.com>
Date: Mon, 26 Jan 2026 18:50:20 -0800
From: Meagan Lloyd <meaganlloyd@...ux.microsoft.com>
To: Frank Li <Frank.li@....com>, David Nyström
<david.nystrom@....tech>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>,
linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org,
Joshua Yeong <joshua.yeong@...rfivetech.com>
Subject: Re: [PATCH v4] i3c: master: Add sysfs option to rescan bus via entdaa
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@....com>
>> 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;
>> + }
>> +
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@....tech>
>>
>>
>> --
>> linux-i3c mailing list
>> linux-i3c@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-i3c
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