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

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Message-ID: <DE840F3C-0CBA-49A5-B9B9-9D279FFAAFFA@fb.com>
Date:   Thu, 8 Sep 2022 20:47:13 +0000
From:   "Jonathan Zhang (Infra)" <jonzhang@...com>
To:     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



> 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’.

> +			continue;
> +
> +		dev_dbg(&adev->dev, "host uid: %llu\n", uid);
> +
> +		if (uid > U32_MAX)
> +			continue;
> +
> 		dev_info(&host->dev, "host supports CXL\n");
> 	}
> 
> -- 
> 2.30.2
> 
>