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

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Message-ID: <6b15a03c-57ae-021a-581c-4f83e58842e8@est.tech>
Date: Thu, 22 Jan 2026 16:47:23 +0100 (CET)
From: David Nyström <david.nystrom@....tech>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>
cc: David Nyström <david.nystrom@....tech>, 
    Alexandre Belloni <alexandre.belloni@...tlin.com>, 
    Frank Li <Frank.Li@....com>, linux-i3c@...ts.infradead.org, 
    linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i3c: master: Add WO sysfs option to re-DDA bus.

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.