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

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Message-ID: <aXeh9ORxy0qxKPBj@lizhi-Precision-Tower-5810>
Date: Mon, 26 Jan 2026 12:18:44 -0500
From: Frank Li <Frank.li@....com>
To: 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 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;
> +	}
> +
> +	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>
>
>
> --
> linux-i3c mailing list
> linux-i3c@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-i3c

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