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

Jonathan Cameron
2024-04-08T08:34:31Z

On Sun, 7 Apr 2024 19:03:23 -0700
PJ Waskiewicz <ppwaskie@kernel.org> wrote:

> On 24/04/07 11:28PM, Lukas Wunner wrote:
>
> Hi Lukas,
>
> > On Sun, Apr 07, 2024 at 02:05:26PM -0700, ppwaskie@kernel.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@kernel.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@kernel.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;
> }
>