On Tue, Jul 29, 2014 at 10:04 PM, Edward Cree <ecree@xxxxxxxxxxxxxx> wrote:
> Not sure if this list is the right place to ask, but:
> I'm working on fallback code in the sfc driver where in some
> configurations the device won't support using VFs, but will still
> advertise them as present [1]. This is discovered at PF probe time, and
> what I want to do is just set sriov_totalvfs to 0 in this case.
>
> As far as I can tell, pci_sriov_set_totalvfs (drivers/pci/iov.c) is the
> function to call, but I'm confused by the comment on that function which
> states "Should be called from PF driver's probe routine with device's
> mutex held."
device_attach()
device_lock(dev); <--------
driver_probe_device()
really_probe()
drv->probe(dev)
ixgbe_probe()
pci_sriov_set_totalvfs()
device_unlock(dev); <--------
>
> Specifically, it's unclear what mutex is meant. struct pci_dev doesn't
> have one; struct pci_sriov /does/ but the struct is only defined in
> drivers/pci/pci.h which I don't appear to be able to include from a
> driver. There's also one in the 'struct device dev' member of struct
> pci_dev, but that seems rather unlikely.
>
> Also, the wording of the comment makes me wonder if being in the PF
> probe routine /implies/ that the mutex is held already, in which case I
> don't have to do anything. This is supported by the only callers,
> igb_probe (via igb_sw_init and igb_probe_vfs) and ixgbe_probe, not
> appearing to take any mutexes before calling pci_sriov_set_totalvfs.
>
> Please CC on replies, as I'm not subscribed to the list.
>
> Thanks,
> -Edward
>
> [1] SFC9120-based NICs support multiple PFs per port and these can be
> used as a kind of "poor-man's SR-IOV" (we're calling it 'PF-IOV') by
> placing the firmware v-switch below the PFs. However, this then
> precludes adding a v-switch above the PF to direct VF traffic, meaning
> that VFs are useless in this configuration. Consequently, our
> configuration tools won't allow VFs and PF-IOV to be enabled
> simultaneously, but bugs or corruption could cause this to happen.
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