Re: [PATCH V6 06/10] cxl/pci: Find the DOE mailbox which supports CDAT

Ira Weiny
2022-02-01T22:18:45Z

On Tue, Feb 01, 2022 at 10:49:47AM -0800, Widawsky, Ben wrote:
> On 22-01-31 23:19:48, ira.weiny@intel.com wrote:
> > From: Ira Weiny <ira.weiny@intel.com>
> >
> > Memory devices need the CDAT data from the device. This data is read
> > from a DOE mailbox which supports the CDAT protocol.
> >
> > Search the DOE auxiliary devices for the one which supports the CDAT
> > protocol. Cache that device to be used for future queries.
> >
> > Signed-off-by: Ira Weiny <ira.weiny@intel.com>

[snip]

> >
> > diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> > index d4ae79b62a14..dcc55c4efd85 100644
> > --- a/drivers/cxl/pci.c
> > +++ b/drivers/cxl/pci.c
> > @@ -536,12 +536,53 @@ static int cxl_dvsec_ranges(struct cxl_dev_state *cxlds)
> > return rc;
> > }
> >
> > +static int cxl_match_cdat_doe_device(struct device *dev, const void *data)
> > +{
> > + const struct cxl_dev_state *cxlds = data;
> > + struct auxiliary_device *adev;
> > + struct pci_doe_dev *doe_dev;
> > +
> > + /* First determine if this auxiliary device belongs to the cxlds */
> > + if (cxlds->dev != dev->parent)
> > + return 0;
>
> I don't understand auxiliary bus but I'm wondering why it's checking the parent
> of the device?

auxiliary_find_device() iterates all the auxiliary devices in the system. This
check was a way for the match function to know if the auxiliary device belongs
to the cxlds we are interested in...

But now that I think about it we could have other auxiliary devices attached
which are not DOE... :-/ So this check is not complete.

FWIW I'm not thrilled with the way auxiliary_find_device() is defined. And now
that I look at it I think the only user of it currently is wrong. They too
have a check like this but it is after another check... :-/

I was hoping to avoid having a list of DOE devices in the cxlds and simply let
the auxiliary bus infrastructure do that somehow. IIRC Jonathan was thinking
along the same lines. I think he actually suggested auxiliary_find_device()...

It would be nice if I could have an aux_find_child() or something which
iterated the auxiliary devices attached to a particular parent device. I've
just not figured out exactly how to implement that better than what I did here.

>
> > +
> > + adev = to_auxiliary_dev(dev);
> > + doe_dev = container_of(adev, struct pci_doe_dev, adev);
> > +
> > + /* If it is one of ours check for the CDAT protocol */
> > + if (pci_doe_supports_prot(doe_dev, PCI_DVSEC_VENDOR_ID_CXL,
> > + CXL_DOE_PROTOCOL_TABLE_ACCESS))
> > + return 1;
> > +
> > + return 0;
> > +}
> > +
> > static int cxl_setup_doe_devices(struct cxl_dev_state *cxlds)
> > {
> > struct device *dev = cxlds->dev;
> > struct pci_dev *pdev = to_pci_dev(dev);
> > + struct auxiliary_device *adev;
> > + int rc;
> >
> > - return pci_doe_create_doe_devices(pdev);
> > + rc = pci_doe_create_doe_devices(pdev);
> > + if (rc)
> > + return rc;
> > +
> > + adev = auxiliary_find_device(NULL, cxlds, &cxl_match_cdat_doe_device);
> > +
> > + if (adev) {
> > + struct pci_doe_dev *doe_dev = container_of(adev,
> > + struct pci_doe_dev,
> > + adev);
> > +
> > + /*
> > + * No reference need be taken. The DOE device lifetime is
> > + * longer that the CXL device state lifetime
> > + */
>
> You're holding a reference to the adev here. Did you mean to drop it?

Does find device get a reference? ... Ah shoot I did not see that.

Yea the reference should be dropped somewhere.

Thanks,
Ira

>
> > + cxlds->cdat_doe = doe_dev;
> > + }
> > +
> > + return 0;
> > }
> >
> > static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> > --
> > 2.31.1
> >