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

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Message-ID: <b07ec317-e916-49bf-bec1-1f954c186457@zohomail.com>
Date: Sun, 28 Sep 2025 18:16:34 +0800
From: Li Ming <ming.li@...omail.com>
To: dave@...olabs.net, 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
Cc: linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] cxl/port: Avoid missing port component registers
 setup

Please ignore this version.
If cxl_port_setup_regs() fails, should remove dport from port->dports. send out v2 to fix it.

Ming

On 9/28/2025 4:27 PM, 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
> 	no chance for component registers setup execution
> 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.
>
> Signed-off-by: Li Ming <ming.li@...omail.com>
> ---
> base-commit: 46037455cbb748c5e85071c95f2244e81986eb58 cxl/next
> ---
>  drivers/cxl/core/port.c | 24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index d5f71eb1ade8..e25f326acd7a 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -1182,6 +1182,18 @@ __devm_cxl_add_dport(struct cxl_port *port, struct device *dport_dev,
>  	if (rc)
>  		return ERR_PTR(rc);
>  
> +	/*
> +	 * Setup port register if this is the first dport showed up. Having
> +	 * a dport also means that there is at least 1 active link.
> +	 */
> +	if (port->nr_dports == 1 &&
> +	    port->component_reg_phys != CXL_RESOURCE_NONE) {
> +		rc = cxl_port_setup_regs(port, port->component_reg_phys);
> +		if (rc)
> +			return ERR_PTR(rc);
> +		port->component_reg_phys = CXL_RESOURCE_NONE;
> +	}
> +
>  	get_device(dport_dev);
>  	rc = devm_add_action_or_reset(host, cxl_dport_remove, dport);
>  	if (rc)
> @@ -1200,18 +1212,6 @@ __devm_cxl_add_dport(struct cxl_port *port, struct device *dport_dev,
>  
>  	cxl_debugfs_create_dport_dir(dport);
>  
> -	/*
> -	 * Setup port register if this is the first dport showed up. Having
> -	 * a dport also means that there is at least 1 active link.
> -	 */
> -	if (port->nr_dports == 1 &&
> -	    port->component_reg_phys != CXL_RESOURCE_NONE) {
> -		rc = cxl_port_setup_regs(port, port->component_reg_phys);
> -		if (rc)
> -			return ERR_PTR(rc);
> -		port->component_reg_phys = CXL_RESOURCE_NONE;
> -	}
> -
>  	return dport;
>  }
>