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

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Date: Mon, 8 Apr 2024 09:34:22 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: PJ Waskiewicz <ppwaskie@...nel.org>
CC: Lukas Wunner <lukas@...ner.de>, 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, 7 Apr 2024 19:03:23 -0700
PJ Waskiewicz <ppwaskie@...nel.org> wrote:

> 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
Move the change log "v2..." etc below the ---
as we don't want it in the long term git log + better to send a fresh
patch in a separate thread.

Other than that seems reasonable to hint it is probably a bios
bug - however I wonder how many other cases we should do this for and
whether it is worth the effort of marking them all?

Jonathan



> 
> 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;
>  	}
>