linux-kernel - Re: [PATCH 1/1] cxl/acpi.c: Add buggy BIOS hint for CXL ACPI lookup failure

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Date: Tue, 9 Apr 2024 08:22:41 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: ppwaskie@...nel.org
Cc: Dan Williams <dan.j.williams@...el.com>, linux-cxl@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] cxl/acpi.c: Add buggy BIOS hint for CXL ACPI lookup
 failure

On Sun, Apr 07, 2024 at 02:05:26PM -0700, ppwaskie@...nel.org wrote:
> From: PJ Waskiewicz <ppwaskie@...nel.org>
> 
> Currently, Type 3 CXL devices (CXL.mem) can train using host CXL
> drivers on Emerald Rapids systems.  However, on some production
> systems from some vendors, a buggy BIOS exists that improperly
> populates the ACPI => PCI mappings.

Can you be more specific about what this ACPI => PCI mapping is?
If you already know what the problem is, I'm sure this is obvious, but
otherwise it's not.

> This leads to the cxl_acpi
> driver to fail probe when it cannot find the root port's _UID, in
> order to look up the device's CXL attributes in the CEDT.
> 
> Add a bit more of a descriptive message that the lookup failure
> could be a bad BIOS, rather than just "failed."
> 
> Signed-off-by: PJ Waskiewicz <ppwaskie@...nel.org>
> ---
>  drivers/cxl/acpi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index af5cb818f84d..56019466a09c 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -504,7 +504,7 @@ static int cxl_get_chbs(struct device *dev, struct acpi_device *hb,
>  
>  	rc = acpi_evaluate_integer(hb->handle, METHOD_NAME__UID, NULL, &uid);
>  	if (rc != AE_OK) {
> -		dev_err(dev, "unable to retrieve _UID\n");
> +		dev_err(dev, "unable to retrieve _UID. Potentially buggy BIOS\n");
>  		return -ENOENT;
>  	}
>  
> -- 
> 2.40.1
>