Re: [PATCH v3 23/28] cxl/acpi: Do not add DSDT disabled ACPI0016 host bridge ports

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

On Tue, 24 Aug 2021 09:07:28 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> From: Alison Schofield <alison.schofield@intel.com>
> 
> During CXL ACPI probe, host bridge ports are discovered by scanning
> the ACPI0017 root port for ACPI0016 host bridge devices. The scan
> matches on the hardware id of "ACPI0016". An issue occurs when an
> ACPI0016 device is defined in the DSDT yet disabled on the platform.
> Attempts by the cxl_acpi driver to add host bridge ports using a
> disabled device fails, and the entire cxl_acpi probe fails.
> 
> The DSDT table includes an _STA method that sets the status and the
> ACPI subsystem has checks available to examine it. One such check is
> in the acpi_pci_find_root() path. Move the call to acpi_pci_find_root()
> to the matching function to prevent this issue when adding either
> upstream or downstream ports.
You could mention that has the side effect that the existing
call in add_host_bridge_uport() is now guarantee not to fail so
can be moved closer to where it is used.  That chunk had
me briefly confused.

> 
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>
> Fixes: 7d4b5ca2e2cb ("cxl/acpi: Add downstream port data to cxl_port instances")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
I'd imagine we want to get this in an early rc so perhaps pull out of
this series.

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


> ---
>  drivers/cxl/acpi.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index 8ae89273f58e..2d8f1ec1abff 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -243,6 +243,9 @@ static struct acpi_device *to_cxl_host_bridge(struct device *dev)
>  {
>  	struct acpi_device *adev = to_acpi_device(dev);
>  
> +	if (!acpi_pci_find_root(adev->handle))
> +		return NULL;
> +
>  	if (strcmp(acpi_device_hid(adev), "ACPI0016") == 0)
>  		return adev;
>  	return NULL;
> @@ -266,10 +269,6 @@ static int add_host_bridge_uport(struct device *match, void *arg)
>  	if (!bridge)
>  		return 0;
>  
> -	pci_root = acpi_pci_find_root(bridge->handle);
> -	if (!pci_root)
> -		return -ENXIO;
> -
>  	dport = find_dport_by_dev(root_port, match);
>  	if (!dport) {
>  		dev_dbg(host, "host bridge expected and not found\n");
> @@ -282,6 +281,7 @@ static int add_host_bridge_uport(struct device *match, void *arg)
>  		return PTR_ERR(port);
>  	dev_dbg(host, "%s: add: %s\n", dev_name(match), dev_name(&port->dev));
>  
> +	pci_root = acpi_pci_find_root(bridge->handle);
>  	ctx = (struct cxl_walk_context){
>  		.dev = host,
>  		.root = pci_root->bus,
>