On Mon, Mar 02, 2020 at 02:33:12PM -0800, Jacob Keller wrote:
> On 3/2/2020 2:25 PM, Bjorn Helgaas wrote:
> >> +int pci_get_dsn(struct pci_dev *dev, u8 dsn[])
> >> +{
> >> + u32 dword;
> >> + int pos;
> >> +
> >> +
> >> + pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DSN);
> >> + if (!pos)
> >> + return -EOPNOTSUPP;
> >> +
> >> + /*
> >> + * The Device Serial Number is two dwords offset 4 bytes from the
> >> + * capability position.
> >> + */
> >> + pos += 4;
> >> + pci_read_config_dword(dev, pos, &dword);
> >> + put_unaligned_le32(dword, &dsn[0]);
> >> + pci_read_config_dword(dev, pos + 4, &dword);
> >> + put_unaligned_le32(dword, &dsn[4]);
> >
> > Since the serial number is a 64-bit value, can we just return a u64
> > and let the caller worry about any alignment and byte-order issues?
> >
> > This would be the only use of asm/unaligned.h in driver/pci, and I
> > don't think DSN should be that special.
>
> I suppose that's fair, but it ends up leaving most callers having to fix
> this immediately after calling this function.
PCIe doesn't impose any structure on the value; it just says the first
dword is the lower DW and the second is the upper DW. As long as we
put that together correctly into a u64, I think further interpretation
is caller-specific.
> > I think it's OK if we return 0 if the device doesn't have a DSN
> > capability. A DSN that actually contains a zero serial number would
> > be dubious at best.
>
> Hmm. I was trying to match how pre-existing code behaved, based on the
> ice and bnxt drivers.
>
> By returning 0s, we'd have to then perform a memcmp or something to
> catch it.
Can you just do this:
dsn = pci_get_dsn(pdev);
if (!dsn)
return NULL;
snprintf(opt_fw_filename, ...);
return opt_fw_filename;
Or am I missing something?
> >> + return 0;
> >> +}
> >> +EXPORT_SYMBOL_GPL(pci_get_dsn);
> >> +
> >> static int __pci_find_next_ht_cap(struct pci_dev *dev, int pos, int ht_cap)
> >> {
> >> int rc, ttl = PCI_FIND_CAP_TTL;
> >> diff --git a/include/linux/pci.h b/include/linux/pci.h
> >> index 3840a541a9de..883562323df3 100644
> >> --- a/include/linux/pci.h
> >> +++ b/include/linux/pci.h
> >> @@ -1045,6 +1045,8 @@ int pci_find_ht_capability(struct pci_dev *dev, int ht_cap);
> >> int pci_find_next_ht_capability(struct pci_dev *dev, int pos, int ht_cap);
> >> struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
> >>
> >> +int pci_get_dsn(struct pci_dev *dev, u8 dsn[]);
> >> +
> >> struct pci_dev *pci_get_device(unsigned int vendor, unsigned int device,
> >> struct pci_dev *from);
> >> struct pci_dev *pci_get_subsys(unsigned int vendor, unsigned int device,
> >> @@ -1699,6 +1701,9 @@ static inline int pci_find_next_capability(struct pci_dev *dev, u8 post,
> >> static inline int pci_find_ext_capability(struct pci_dev *dev, int cap)
> >> { return 0; }
> >>
> >> +static inline int pci_get_dsn(struct pci_dev *dev, u8 dsn[])
> >> +{ return -EOPNOTSUPP; }
> >> +
> >> /* Power management related routines */
> >> static inline int pci_save_state(struct pci_dev *dev) { return 0; }
> >> static inline void pci_restore_state(struct pci_dev *dev) { }
> >> --
> >> 2.25.0.368.g28a2d05eebfb
> >>
