linux-kernel - Re: [PATCH v2 1/1] cxl/port: Avoid missing port component registers setup

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Message-ID: <20250930005053.2jme7stunhrmp3om@offworld>
Date: Mon, 29 Sep 2025 17:50:53 -0700
From: Davidlohr Bueso <dave@...olabs.net>
To: Li Ming <ming.li@...omail.com>
Cc: jonathan.cameron@...wei.com, dave.jiang@...el.com,
	alison.schofield@...el.com, vishal.l.verma@...el.com,
	ira.weiny@...el.com, dan.j.williams@...el.com,
	shiju.jose@...wei.com, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] cxl/port: Avoid missing port component registers
 setup

On Sun, 28 Sep 2025, Li Ming wrote:

>port->nr_dports is used to represent how many dports added to the cxl
>port, it will increase in add_dport() when a new dport is being added to
>the cxl port, but it will not be reduced when a dport is removed from
>the cxl port.
>
>Currently, when the first dport is added to a cxl port, it will trigger
>component registers setup on the cxl port, the implementation is using
>port->nr_dports to confirm if the dport is the first dport.
>
>A corner case here is that adding dport could fail after port->nr_dports
>updating and before checking port->nr_dports for component registers
>setup. If the failure happens during the first dport attaching, it will
>cause that CXL subsystem has not chance to execute component registers
>setup for the cxl port. the failure flow like below:
>
>port->nr_dports = 0
>dport 1 adding to the port:
>	add_dport()	# port->nr_dports: 1
>	failed on devm_add_action_or_reset() or sysfs_create_link()
>	return error	# port->nr_dports: 1
>dport 2 adding to the port:
>	add_dport()	# port->nr_dports: 2
>	no failure
>	skip component registers setup because of port->nr_dports is 2
>
>The solution here is that moving component registers setup closer to
>add_dport(), so if add_dport() is executed correctly for the first
>dport, component registers setup on the port will be executed
>immediately after that.

Reviewed-by: Davidlohr Bueso <dave@...olabs.net>