linux-kernel - Re: [PATCH v3] i3c: master: Add sysfs option to rescan bus via entdaa

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Message-ID: <aXOfe/T0gPPbTiHx@lizhi-Precision-Tower-5810>
Date: Fri, 23 Jan 2026 11:19:07 -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 v3] i3c: master: Add sysfs option to rescan bus via entdaa

On Fri, Jan 23, 2026 at 08:55:37AM +0100, David Nyström wrote:
> Add the ability to rescan the i3c bus from userspace, i.e. provoke
> an ENTDDA. 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.

AI helpped rephrase

Allow userspace to request a dynamic address assignment, which is
useful for devices with broken hot-join support or devices that boot
slowly and may miss the initial DDA during system startup.

Need update ABI document

Documentation/ABI/testing/sysfs-bus-i3c

Frank
>
> Signed-off-by: David Nyström <david.nystrom@....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
> ---
>  drivers/i3c/master.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> 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>
>