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SubjectRe: [PATCH 09/15] cxl/acpi: Determine PCI host bridge's ACPI UID
On Wed, 31 Aug 2022 10:15:57 +0200
Robert Richter <rrichter@amd.com> wrote:

> The UID is needed to read the RCH's CEDT entry with the RCRB base
> address. Determine the host's UID from its ACPI fw node.
>
> Signed-off-by: Robert Richter <rrichter@amd.com>
> ---
> drivers/cxl/acpi.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index f9cdf23a91a8..b3146b7ae922 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -368,8 +368,20 @@ struct pci_host_bridge *cxl_find_next_rch(struct pci_host_bridge *host)
> static int __init cxl_restricted_host_probe(struct platform_device *pdev)
> {
> struct pci_host_bridge *host = NULL;
> + struct acpi_device *adev;
> + unsigned long long uid = ~0;
>
> while ((host = cxl_find_next_rch(host)) != NULL) {
> + adev = ACPI_COMPANION(&host->dev);
> + if (!adev || !adev->pnp.unique_id ||
> + (kstrtoull(adev->pnp.unique_id, 10, &uid) < 0))

There is an acpi_device_uid() accessor function that should probably be
used here.

Also, should a fialure to convert to an integer (or one within
limits) be something we paper over? Feels like we should fail
hard if that happens.

Admittedly I can't immediately find any spec that states that
the _UID should be either integer or under 32 bits...
ACPI allows a string and CXL just says it's 4 bytes long.

> + continue;
> +
> + dev_dbg(&adev->dev, "host uid: %llu\n", uid);
> +
> + if (uid > U32_MAX)
> + continue;
> +
> dev_info(&host->dev, "host supports CXL\n");
> }
>

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