Re: [PATCH v2 2/3] cxl/port: Use scoped_guard()/guard() to drop device_lock() for cxl_port

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Mon, 26 Aug 2024 08:30:57 +0000
Li Ming <ming4.li@intel.com> wrote:

> A device_lock() and device_unlock() pair can be replaced by a cleanup
> helper scoped_guard() or guard(), that can enhance code readability. In
> CXL subsystem, still use device_lock() and device_unlock() pairs for cxl
> port resource protection, most of them can be replaced by a
> scoped_guard() or a guard() simply.
> 
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Li Ming <ming4.li@intel.com>

Hi Li Ming,

The advantages of previous patch become clearer here.  So
overall I think I'm convinced it's worth making the change.

Follow on comment below,

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index b50dda6610e3..7b87b5142fa7 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c

> @@ -1561,40 +1556,38 @@ static int add_port_attach_ep(struct cxl_memdev *cxlmd,
>  		return -EAGAIN;
>  	}
>  
> -	device_lock(&parent_port->dev);
> -	if (!parent_port->dev.driver) {
> -		dev_warn(&cxlmd->dev,
> -			 "port %s:%s disabled, failed to enumerate CXL.mem\n",
> -			 dev_name(&parent_port->dev), dev_name(uport_dev));
> -		port = ERR_PTR(-ENXIO);
> -		goto out;
> -	}

As per comment in previous patch, I'd pull the instantiation of
port down here.  That way constructor and destructor are at least nearby
and the ordering is more what I'd expect.

> +	scoped_guard(device, &parent_port->dev) {
> +		if (!parent_port->dev.driver) {
> +			dev_warn(&cxlmd->dev,
> +				 "port %s:%s disabled, failed to enumerate CXL.mem\n",
> +				 dev_name(&parent_port->dev), dev_name(uport_dev));
> +			return -ENXIO;
> +		}
> +
> +		port = find_cxl_port_at(parent_port, dport_dev, &dport);
> +		if (!port) {
> +			component_reg_phys = find_component_registers(uport_dev);
> +			port = devm_cxl_add_port(&parent_port->dev, uport_dev,
> +						 component_reg_phys, parent_dport);
> +			if (IS_ERR(port))
> +				return PTR_ERR(port);
>  
> -	port = find_cxl_port_at(parent_port, dport_dev, &dport);
> -	if (!port) {
> -		component_reg_phys = find_component_registers(uport_dev);
> -		port = devm_cxl_add_port(&parent_port->dev, uport_dev,
> -					 component_reg_phys, parent_dport);
> -		/* retry find to pick up the new dport information */
> -		if (!IS_ERR(port))
> +			/* retry find to pick up the new dport information */
>  			port = find_cxl_port_at(parent_port, dport_dev, &dport);
> +			if (!port)
> +				return -ENXIO;
> +		}
>  	}
> -out:
> -	device_unlock(&parent_port->dev);
>  
> -	if (IS_ERR(port))
> -		rc = PTR_ERR(port);
> -	else {
> -		dev_dbg(&cxlmd->dev, "add to new port %s:%s\n",
> -			dev_name(&port->dev), dev_name(port->uport_dev));
> -		rc = cxl_add_ep(dport, &cxlmd->dev);
> -		if (rc == -EBUSY) {
> -			/*
> -			 * "can't" happen, but this error code means
> -			 * something to the caller, so translate it.
> -			 */
> -			rc = -ENXIO;
> -		}
> +	dev_dbg(&cxlmd->dev, "add to new port %s:%s\n",
> +		dev_name(&port->dev), dev_name(port->uport_dev));
> +	rc = cxl_add_ep(dport, &cxlmd->dev);
> +	if (rc == -EBUSY) {
> +		/*
> +		 * "can't" happen, but this error code means
> +		 * something to the caller, so translate it.
> +		 */
> +		rc = -ENXIO;
>  	}
>  
>  	return rc;