Re: [PATCH v3 04/10] PCI/RCEC: Add pcie_walk_rcec() to walk associated RCiEPs

Kelley, Sean V
2020-09-04T22:19:15Z

Hi Bjorn,

Quick question below...

On Wed, 2020-09-02 at 14:55 -0700, Sean V Kelley wrote:
> Hi Bjorn,
>
> On Wed, 2020-09-02 at 14:00 -0500, Bjorn Helgaas wrote:
> > On Wed, Aug 12, 2020 at 09:46:53AM -0700, Sean V Kelley wrote:
> > > From: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
> > >
> > > When an RCEC device signals error(s) to a CPU core, the CPU core
> > > needs to walk all the RCiEPs associated with that RCEC to check
> > > errors. So add the function pcie_walk_rcec() to walk all RCiEPs
> > > associated with the RCEC device.
> > >
> > > Co-developed-by: Sean V Kelley <sean.v.kelley@intel.com>
> > > Signed-off-by: Sean V Kelley <sean.v.kelley@intel.com>
> > > Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
> > > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > ---
> > > drivers/pci/pci.h | 4 +++
> > > drivers/pci/pcie/rcec.c | 76
> > > +++++++++++++++++++++++++++++++++++++++++
> > > 2 files changed, 80 insertions(+)
> > >
> > > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> > > index bd25e6047b54..8bd7528d6977 100644
> > > --- a/drivers/pci/pci.h
> > > +++ b/drivers/pci/pci.h
> > > @@ -473,9 +473,13 @@ static inline void pci_dpc_init(struct
> > > pci_dev
> > > *pdev) {}
> > > #ifdef CONFIG_PCIEPORTBUS
> > > void pci_rcec_init(struct pci_dev *dev);
> > > void pci_rcec_exit(struct pci_dev *dev);
> > > +void pcie_walk_rcec(struct pci_dev *rcec, int (*cb)(struct
> > > pci_dev
> > > *, void *),
> > > + void *userdata);
> > > #else
> > > static inline void pci_rcec_init(struct pci_dev *dev) {}
> > > static inline void pci_rcec_exit(struct pci_dev *dev) {}
> > > +static inline void pcie_walk_rcec(struct pci_dev *rcec, int
> > > (*cb)(struct pci_dev *, void *),
> > > + void *userdata) {}
> > > #endif
> > >
> > > #ifdef CONFIG_PCI_ATS
> > > diff --git a/drivers/pci/pcie/rcec.c b/drivers/pci/pcie/rcec.c
> > > index 519ae086ff41..405f92fcdf7f 100644
> > > --- a/drivers/pci/pcie/rcec.c
> > > +++ b/drivers/pci/pcie/rcec.c
> > > @@ -17,6 +17,82 @@
> > >
> > > #include "../pci.h"
> > >
> > > +static int pcie_walk_rciep_devfn(struct pci_bus *bus, int
> > > (*cb)(struct pci_dev *, void *),
> > > + void *userdata, const unsigned long
> > > bitmap)
> > > +{
> > > + unsigned int devn, fn;
> > > + struct pci_dev *dev;
> > > + int retval;
> > > +
> > > + for_each_set_bit(devn, &bitmap, 32) {
> > > + for (fn = 0; fn < 8; fn++) {
> > > + dev = pci_get_slot(bus, PCI_DEVFN(devn, fn));
> >
> > Wow, this is a lot of churning to call pci_get_slot() 256 times per
> > bus for the "associated bus numbers" case where we pass a bitmap of
> > 0xffffffff. They didn't really make it easy for software when they
> > added the next/last bus number thing.
> >
> > Just thinking out loud here. What if we could set dev->rcec during
> > enumeration, and then use that to build pcie_walk_rcec()?
>
> I think follow what you are doing.
>
> As we enumerate an RCEC, use the time to discover RCiEPs and
> associate
> each RCiEP's dev->rcec. Although BIOS already set the bitmap for this
> specific RCEC, it's more efficient to simply discover the devices
> through the bus walk and verify each one found against the bitmap.
>
> Further, while we can be certain that an RCiEP found with a matching
> device no. in a bitmap for an associated RCEC is correct, we cannot
> be
> certain that any RCiEP found on another bus range is correct unless
> we
> verify the bus is within that next/last bus range.
>
> Finally, that's where find_rcec() callback for rcec_assoc_rciep()
> does
> double duty by also checking on the "on-a-separate-bus" case captured
> potentially by find_rcec() during an RCiEP's bus walk.
>
>
> > bool rcec_assoc_rciep(rcec, rciep)
> > {
> > if (rcec->bus == rciep->bus)
> > return (rcec->bitmap contains rciep->devfn);
> >
> > return (rcec->next/last contains rciep->bus);
> > }
> >
> > link_rcec(dev, data)
> > {
> > struct pci_dev *rcec = data;
> >
> > if ((dev is RCiEP) && rcec_assoc_rciep(rcec, dev))
> > dev->rcec = rcec;
> > }
> >
> > find_rcec(dev, data)
> > {
> > struct pci_dev *rciep = data;
> >
> > if ((dev is RCEC) && rcec_assoc_rciep(dev, rciep))
> > rciep->rcec = dev;
> > }
> >
> > pci_setup_device
> > ...

I just noticed your use of pci_setup_device(). Are you suggesting
moving the call to pci_rcec_init() out of pci_init_capabilities() and
move it into pci_setup_device()? If so, would pci_rcec_exit() still
remain in pci_release_capabilities()?

I'm just wondering if it could just remain in pci_init_capabilities().

Thanks,

Sean

> > if (dev is RCEC) {
> > pci_rcec_init(dev) # cache bitmap, next/last bus
> > #
> > pci_walk_bus(root_bus, link_rcec, dev); # link any RCiEP
> > already found
> > }
> > if (dev is RCiEP) {
> > pci_walk_bus(root_bus, find_rcec, dev); # link any RCEC already
> > found
> > }
> >
> > Now we should have a valid dev->rcec for everything we've
> > enumerated.
> >
> > struct walk_rcec_data {
> > struct pci_dev *rcec;
> > ... user_callback;
> > void *user_data;
> > };
> >
> > pcie_rcec_helper(dev, callback, data)
> > {
> > struct walk_rcec_data *rcec_data = data;
> >
> > if (dev->rcec == rcec_data->rcec)
> > rcec_data->user_callback(dev, rcec_data->user_data);
> > }
> >
> > pcie_walk_rcec(rcec, callback, data)
> > {
> > struct walk_rcec_data rcec_data;
> > ...
> > rcec_data.rcec = rcec;
> > rcec_data.user_callback = callback;
> > rcec_data.user_data = data;
> > pci_walk_bus(root_bus, pcie_rcec_helper, &rcec_data);
> > }
> >
> > I hate having to walk the bus so many times, but I do like the fact
> > that in the runtime path (pcie_walk_rcec()) we don't have to do 256
> > pci_get_slot() calls per bus, almost all of which are going to
> > fail.
>
> That's really the trade-off and it's slightly harder to follow.
>
> Will implement and see how it looks / tests.
>
>
> > > + if (!dev)
> > > + continue;
> > > +
> > > + if (pci_pcie_type(dev) != PCI_EXP_TYPE_RC_END)
> > > {
> > > + pci_dev_put(dev);
> > > + continue;
> > > + }
> > > +
> > > + retval = cb(dev, userdata);
> > > + pci_dev_put(dev);
> > > + if (retval)
> > > + return retval;
> > > + }
> > > + }
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +/**
> > > + * pcie_walk_rcec - Walk RCiEP devices associating with RCEC and
> > > call callback.
> > > + * @rcec RCEC whose RCiEP devices should be walked.
> > > + * @cb Callback to be called for each RCiEP device found.
> > > + * @userdata Arbitrary pointer to be passed to callback.
> > > + *
> > > + * Walk the given RCEC. Call the provided callback on each RCiEP
> > > device found.
> > > + *
> > > + * We check the return of @cb each time. If it returns anything
> > > + * other than 0, we break out.
> > > + */
> > > +void pcie_walk_rcec(struct pci_dev *rcec, int (*cb)(struct
> > > pci_dev
> > > *, void *),
> > > + void *userdata)
> > > +{
> > > + u8 nextbusn, lastbusn;
> > > + struct pci_bus *bus;
> > > + unsigned int bnr;
> > > +
> > > + if (!rcec->rcec_cap)
> > > + return;
> > > +
> > > + /* Find RCiEP devices on the same bus as the RCEC */
> > > + if (pcie_walk_rciep_devfn(rcec->bus, cb, userdata, rcec-
> > > > rcec_ext->bitmap))
> > > + return;
> > > +
> > > + /* Check whether RCEC BUSN register is present */
> > > + if (rcec->rcec_ext->ver < PCI_RCEC_BUSN_REG_VER)
> > > + return;
> > > +
> > > + nextbusn = rcec->rcec_ext->nextbusn;
> > > + lastbusn = rcec->rcec_ext->lastbusn;
> > > +
> > > + /* All RCiEP devices are on the same bus as the RCEC */
> > > + if (nextbusn == 0xff && lastbusn == 0x00)
> > > + return;
> > > +
> > > + for (bnr = nextbusn; bnr <= lastbusn; bnr++) {
> >
> > I think we also need to skip the RCEC bus here, don't we? 7.9.10.3
> > says the Associated Bus Numbers register does not indicate
> > association
> > between an EC and any Function on the same bus number as the EC
> > itself. Something like this:
> >
> > if (bnr == rcec->bus->number)
> > continue;
>
> Correct. Although it is permitted to include the bus number for the
> RCEC in that range (not sure why), skipping the RCEC's should be
> done.
>
> Will do.
>
> > > + bus = pci_find_bus(pci_domain_nr(rcec->bus), bnr);
> > > + if (!bus)
> > > + continue;
> > > +
> > > + /* Find RCiEP devices on the given bus */
> > > + if (pcie_walk_rciep_devfn(bus, cb, userdata,
> > > 0xffffffff))
> > > + return;
> > > + }
> > > +}
> > > +
> > > void pci_rcec_init(struct pci_dev *dev)
> > > {
> > > u32 rcec, hdr, busn;
> > > --
> > > 2.28.0
> > >