Messages in this thread | | | Date | Thu, 8 Sep 2022 15:31:21 -0700 | From | Dan Williams <> | Subject | Re: [PATCH 09/15] cxl/acpi: Determine PCI host bridge's ACPI UID |
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Jonathan Zhang (Infra) wrote: > > > > On Sep 8, 2022, at 2:10 PM, Dan Williams <dan.j.williams@intel.com> wrote: > > > > !-------------------------------------------------------------------| > > This Message Is From an External Sender > > > > |-------------------------------------------------------------------! > > > > Jonathan Zhang (Infra) wrote: > >> > >> > >>> On Aug 31, 2022, at 1:15 AM, 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)) > >> The UID field holds 4 bytes of ASCII characters. kstrtoull() would fail > >> if the UID field has value such as ‘CX03’. > > > > The UID field is not 4 ASCII characters. > > > > We went through this before in the original code in > > drivers/cxl/acpi.c::add_host_bridge_dport(). > > > > The CEDT.CHBS defines _UID as an integer so use acpi_evaluate_integer() > > to retrieve the UID to perform the comparison. I thought there was an > > errata filed to clarify this, but it seems the current spec still just > > says "value". The CFMWS also places _UID values in the target list, > > those are also handled as integers. > > ACPI 6.4 spec section 6.1.12 describes _UID, it says the return value is: > An Integer or String containing the Unique ID. > > In the BIOS I see, the _UIDs of PCIe devices hold ASCII characters (not NULL > terminated).
ASCII characters without NULL termination means that data can be treated as binary data which is what current CFMWWS parsing code chooses to do. I think a spec clarification is needed to make resolve the ambiguity.
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