Re: [PATCH v3 23/28] cxl/acpi: Do not add DSDT disabled ACPI0016 host bridge ports

[Dan Williams <dan.j.williams@intel.com>]

On Thu, Sep 2, 2021 at 11:30 AM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Tue, 24 Aug 2021 09:07:28 -0700
> Dan Williams <dan.j.williams@intel.com> wrote:
>
> > From: Alison Schofield <alison.schofield@intel.com>
> >
> > During CXL ACPI probe, host bridge ports are discovered by scanning
> > the ACPI0017 root port for ACPI0016 host bridge devices. The scan
> > matches on the hardware id of "ACPI0016". An issue occurs when an
> > ACPI0016 device is defined in the DSDT yet disabled on the platform.
> > Attempts by the cxl_acpi driver to add host bridge ports using a
> > disabled device fails, and the entire cxl_acpi probe fails.
> >
> > The DSDT table includes an _STA method that sets the status and the
> > ACPI subsystem has checks available to examine it. One such check is
> > in the acpi_pci_find_root() path. Move the call to acpi_pci_find_root()
> > to the matching function to prevent this issue when adding either
> > upstream or downstream ports.
> You could mention that has the side effect that the existing
> call in add_host_bridge_uport() is now guarantee not to fail so
> can be moved closer to where it is used.  That chunk had
> me briefly confused.
>
> >
> > Suggested-by: Dan Williams <dan.j.williams@intel.com>
> > Signed-off-by: Alison Schofield <alison.schofield@intel.com>
> > Fixes: 7d4b5ca2e2cb ("cxl/acpi: Add downstream port data to cxl_port instances")
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> I'd imagine we want to get this in an early rc so perhaps pull out of
> this series.

I'm going to keep it in this series because it causes merge conflicts
for what follows, but I'll merge it independently of the follow-on
reworks which may need to wait another cycle.

>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>
>
> > ---
> >  drivers/cxl/acpi.c |    8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> > index 8ae89273f58e..2d8f1ec1abff 100644
> > --- a/drivers/cxl/acpi.c
> > +++ b/drivers/cxl/acpi.c
> > @@ -243,6 +243,9 @@ static struct acpi_device *to_cxl_host_bridge(struct device *dev)
> >  {
> >       struct acpi_device *adev = to_acpi_device(dev);
> >
> > +     if (!acpi_pci_find_root(adev->handle))
> > +             return NULL;
> > +
> >       if (strcmp(acpi_device_hid(adev), "ACPI0016") == 0)
> >               return adev;
> >       return NULL;
> > @@ -266,10 +269,6 @@ static int add_host_bridge_uport(struct device *match, void *arg)
> >       if (!bridge)
> >               return 0;
> >
> > -     pci_root = acpi_pci_find_root(bridge->handle);
> > -     if (!pci_root)
> > -             return -ENXIO;
> > -
> >       dport = find_dport_by_dev(root_port, match);
> >       if (!dport) {
> >               dev_dbg(host, "host bridge expected and not found\n");
> > @@ -282,6 +281,7 @@ static int add_host_bridge_uport(struct device *match, void *arg)
> >               return PTR_ERR(port);
> >       dev_dbg(host, "%s: add: %s\n", dev_name(match), dev_name(&port->dev));
> >
> > +     pci_root = acpi_pci_find_root(bridge->handle);
> >       ctx = (struct cxl_walk_context){
> >               .dev = host,
> >               .root = pci_root->bus,
> >
>
>