Re: [PATCH v5 18/40] cxl/pmem: Introduce a find_cxl_root() helper

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

On Mon, Jan 31, 2022 at 8:20 AM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Wed, 26 Jan 2022 15:59:07 -0800
> Dan Williams <dan.j.williams@intel.com> wrote:
>
> > In preparation for switch port enumeration while also preserving the
> > potential for multi-domain / multi-root CXL topologies. Introduce a
> > 'struct device' generic mechanism for retrieving a root CXL port, if one
> > is registered. Note that the only know multi-domain CXL configurations
> > are running the cxl_test unit test on a system that also publishes an
> > ACPI0017 device.
> >
> > With this in hand the nvdimm-bridge lookup can be with
> > device_find_child() instead of bus_find_device() + custom mocked lookup
> > infrastructure in cxl_test.
> >
> > The mechanism looks for a 2nd level port since the root level topology
> > is platform-firmware specific and the 2nd level down follows standard
> > PCIe topology expectations. The cxl_acpi 2nd level is associated with a
> > PCIe Root Port.
> >
> > Reported-by: Ben Widawsky <ben.widawsky@intel.com>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> A question inline.
>
> Thanks,
>
> Jonathan
>
> > ---
> > Changes since v4:
> > - reset @iter each loop otherwise only the first dport can be scanned.
> >
> >  drivers/cxl/core/pmem.c       |   14 ++++++++---
> >  drivers/cxl/core/port.c       |   50 +++++++++++++++++++++++++++++++++++++++++
> >  drivers/cxl/cxl.h             |    1 +
> >  tools/testing/cxl/Kbuild      |    2 --
> >  tools/testing/cxl/mock_pmem.c |   24 --------------------
> >  5 files changed, 61 insertions(+), 30 deletions(-)
> >  delete mode 100644 tools/testing/cxl/mock_pmem.c
> >
> > diff --git a/drivers/cxl/core/pmem.c b/drivers/cxl/core/pmem.c
> > index 40b3f5030496..8de240c4d96b 100644
> > --- a/drivers/cxl/core/pmem.c
> > +++ b/drivers/cxl/core/pmem.c
> > @@ -57,24 +57,30 @@ bool is_cxl_nvdimm_bridge(struct device *dev)
> >  }
> >  EXPORT_SYMBOL_NS_GPL(is_cxl_nvdimm_bridge, CXL);
> >
> > -__mock int match_nvdimm_bridge(struct device *dev, const void *data)
> > +static int match_nvdimm_bridge(struct device *dev, void *data)
> >  {
> >       return is_cxl_nvdimm_bridge(dev);
> >  }
> >
> >  struct cxl_nvdimm_bridge *cxl_find_nvdimm_bridge(struct cxl_nvdimm *cxl_nvd)
> >  {
> > +     struct cxl_port *port = find_cxl_root(&cxl_nvd->dev);
> >       struct device *dev;
> >
> > -     dev = bus_find_device(&cxl_bus_type, NULL, cxl_nvd, match_nvdimm_bridge);
> > +     if (!port)
> > +             return NULL;
> > +
> > +     dev = device_find_child(&port->dev, NULL, match_nvdimm_bridge);
> > +     put_device(&port->dev);
> > +
> >       if (!dev)
> >               return NULL;
> > +
> >       return to_cxl_nvdimm_bridge(dev);
> >  }
> >  EXPORT_SYMBOL_NS_GPL(cxl_find_nvdimm_bridge, CXL);
> >
> > -static struct cxl_nvdimm_bridge *
> > -cxl_nvdimm_bridge_alloc(struct cxl_port *port)
> > +static struct cxl_nvdimm_bridge *cxl_nvdimm_bridge_alloc(struct cxl_port *port)
> >  {
> >       struct cxl_nvdimm_bridge *cxl_nvb;
> >       struct device *dev;
> > diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> > index 4c921c49f967..6447f12ef71d 100644
> > --- a/drivers/cxl/core/port.c
> > +++ b/drivers/cxl/core/port.c
> > @@ -457,6 +457,56 @@ int devm_cxl_register_pci_bus(struct device *host, struct device *uport,
> >  }
> >  EXPORT_SYMBOL_NS_GPL(devm_cxl_register_pci_bus, CXL);
> >
> > +/* Find a 2nd level CXL port that has a dport that is an ancestor of @match */
> > +static int match_cxl_root_child(struct device *dev, const void *match)
> > +{
> > +     const struct device *iter = NULL;
> > +     struct cxl_port *port, *parent;
> > +     struct cxl_dport *dport;
> > +
> > +     if (!is_cxl_port(dev))
> > +             return 0;
> > +
> > +     port = to_cxl_port(dev);
> > +     if (is_cxl_root(port))
> > +             return 0;
> > +
> > +     parent = to_cxl_port(port->dev.parent);
> > +     if (!is_cxl_root(parent))
> > +             return 0;
> > +
> > +     cxl_device_lock(&port->dev);
> > +     list_for_each_entry(dport, &port->dports, list) {
> > +             iter = match;
>
> This confuses me.  In the call below to bus_find_device()
> data == NULL, which ends up as match here.

I think you misread, @start is NULL @data becomes @match as the
starting point for the search.

>
> So how does that ever find a match?
>
> > +             while (iter) {
> > +                     if (iter == dport->dport)
> > +                             goto out;
> > +                     iter = iter->parent;
> > +             }
> > +     }
> > +out:
> > +     cxl_device_unlock(&port->dev);
> > +
> > +     return !!iter;
>
> return iter; should be sufficient as docs just say non zero for a match
> in bus_find_device() match functions.

drivers/cxl/core/port.c:488:16: error: returning ‘const struct device
*’ from a function with return type ‘int’ makes integer from pointer
without a cast [-Werror=int-conversion]

>
> > +}
> > +
> > +struct cxl_port *find_cxl_root(struct device *dev)
> > +{
> > +     struct device *port_dev;
> > +     struct cxl_port *root;
> > +
> > +     port_dev =
> > +             bus_find_device(&cxl_bus_type, NULL, dev, match_cxl_root_child);
>
> Line breaking is rather ugly to my eye.  Perhaps break
> parameter list up instead?

This is what clang-format picked, but yes it's a tag ugly. I'll go
ahead and s/match_cxl_root_child/match_root_child/ since there are no
public symbol namespace issues with this static helper.