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

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Message-ID: <e2749038-bf78-47a6-83da-96f02bd75599@intel.com>
Date: Mon, 29 Sep 2025 09:53:58 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Li Ming <ming.li@...omail.com>, dave@...olabs.net,
 jonathan.cameron@...wei.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 v2 1/1] cxl/port: Avoid missing port component registers
 setup



On 9/28/25 3:14 AM, 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.
> 
> Signed-off-by: Li Ming <ming.li@...omail.com>

That makes sense. Please add a fixes tag. The commit in cxl/next should be stable.

Reviewed-by: Dave Jiang <dave.jiang@...el.com>

> ---
> v2:
> - remove dport from port->dports in case of component registers setup
>   failed.
> 
> base-commit: 46037455cbb748c5e85071c95f2244e81986eb58 cxl/next
> ---
>  drivers/cxl/core/port.c | 26 ++++++++++++++------------
>  1 file changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index d5f71eb1ade8..8128fd2b5b31 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -1182,6 +1182,20 @@ __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) {
> +			xa_erase(&port->dports, (unsigned long)dport->dport_dev);
> +			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 +1214,6 @@ __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;
>  }
>