Re: [PATCH v4 09/23] cxl: Add helper function to retrieve ACPI handle of CXL root device

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

On Wed, 19 Apr 2023 13:21:55 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> Provide a helper to find the ACPI0017 device in order to issue the _DSM.
> The helper will take the 'struct device' from a cxl_port and iterate until
> the root device is reached. The ACPI handle will be returned from the root
> device.
> 
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>

Question inline.  If the answer is no then this looks fine to me.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>


> +/**
> + * cxl_acpi_get_rootdev_handle - get the ACPI handle of the CXL root device
> + * @dev: 'struct device' to start searching from. Should be from cxl_port->dev.
> + *
> + * Return: acpi_handle on success, errptr of errno on error.
> + *
> + * Looks for the ACPI0017 device and return the ACPI handle
> + **/

Could we implement this in terms of find_cxl_root()?  I think that will
end up giving you the same device though I haven't tested it.

> +acpi_handle cxl_acpi_get_rootdev_handle(struct device *dev)
> +{
> +	struct device *itr = dev;
> +	struct device *root_dev;
> +	acpi_handle handle;
> +
> +	if (!dev)
> +		return ERR_PTR(-EINVAL);
> +
> +	while (itr->parent) {
> +		root_dev = itr;
> +		itr = itr->parent;
> +	}
> +
> +	if (!dev_is_platform(root_dev))
> +		return ERR_PTR(-ENODEV);
> +
> +	handle = ACPI_HANDLE(root_dev);
> +	if (!handle)
> +		return ERR_PTR(-ENODEV);
> +
> +	return handle;
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_acpi_get_rootdev_handle, CXL);