Messages in this thread | | | From | "Jonathan Zhang (Infra)" <> | Subject | Re: [PATCH 09/15] cxl/acpi: Determine PCI host bridge's ACPI UID | Date | Thu, 8 Sep 2022 22:41:48 +0000 |
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> On Sep 8, 2022, at 3:31 PM, Dan Williams <dan.j.williams@intel.com> wrote: > > !-------------------------------------------------------------------| > This Message Is From an External Sender > > |-------------------------------------------------------------------! > > 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.
Agreed. In this case, ACPI spec should be referred to.
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