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

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Date: Sun, 7 Apr 2024 19:03:23 -0700
From: PJ Waskiewicz <ppwaskie@...nel.org>
To: Lukas Wunner <lukas@...ner.de>
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 24/04/07 11:28PM, Lukas Wunner wrote:

Hi Lukas,

> On Sun, Apr 07, 2024 at 02:05:26PM -0700, ppwaskie@...nel.org wrote:
> > --- 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;
> >  	}
> 
> dev_err(dev, FW_BUG "unable to retrieve _UID\n");
>              ^^^^^^
> 
> There's a macro for that.

Doh...it's been awhile since I've crossed buggy BIOS's.  Thanks for the
review and comment.

Updated patch:

cxl/acpi.c: Add buggy BIOS hint for CXL ACPI lookup failure

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.  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."

v2: Updated message to use existing FW_BUG macro

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..d321cfbd4682 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, FW_BUG "unable to retrieve _UID\n");
 		return -ENOENT;
 	}
 
-- 
2.40.1