Messages in this thread | | | Date | Thu, 1 Sep 2022 11:41:33 +0100 | From | Jonathan Cameron <> | Subject | Re: [PATCH 09/15] cxl/acpi: Determine PCI host bridge's ACPI UID |
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On Thu, 1 Sep 2022 08:53:36 +0200 Robert Richter <rrichter@amd.com> wrote:
> On 31.08.22 12:00:27, Jonathan Cameron wrote: > > On Wed, 31 Aug 2022 10:15:57 +0200 > > Robert Richter <rrichter@amd.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@amd.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)) > > > > There is an acpi_device_uid() accessor function that should probably be > > used here. > > That accessor actually does not help really, there is no null pointer > check for adev. Using it actually adds more complexity since another > variable is introduced plus you need to look at the function's > implementation anyway. > > The adev->pnp.unique_id access pattern is widely used in the kernel, I > don't expect changes in the data struct here.
Ok.
> > > Also, should a fialure to convert to an integer (or one within > > limits) be something we paper over? Feels like we should fail > > hard if that happens. > > This is a real corner case and close to a broken firmware > implementation. I think current dbg messages are good to find where > the detection stops.
Hmm. I don't like papering over such bugs as it leads to people not fixing their bios as early as they otherwise would, but fair enough I guess.
> > > Admittedly I can't immediately find any spec that states that > > the _UID should be either integer or under 32 bits... > > ACPI allows a string and CXL just says it's 4 bytes long. > > IIRC the UID can be implemented as string or 8 bytes, there is no > limitation then. That's why the range check below. Ok.
All queries answered so
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > -Robert > > > > > > + continue; > > > + > > > + dev_dbg(&adev->dev, "host uid: %llu\n", uid); > > > + > > > + if (uid > U32_MAX) > > > + continue; > > > + > > > dev_info(&host->dev, "host supports CXL\n"); > > > } > > > > >
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