linux-kernel - Re: [PATCH 09/15] cxl/acpi: Determine PCI host bridge's ACPI UID

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Message-ID: <631a5a27f22ac_166f29479@dwillia2-xfh.jf.intel.com.notmuch>
Date:   Thu, 8 Sep 2022 14:10:00 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Jonathan Zhang (Infra)" <jonzhang@...com>,
        Robert Richter <rrichter@....com>
CC:     Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>
Subject: Re: [PATCH 09/15] cxl/acpi: Determine PCI host bridge's ACPI UID

Jonathan Zhang (Infra) wrote:
> 
> 
> > On Aug 31, 2022, at 1:15 AM, Robert Richter <rrichter@....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@....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.