On 3/2/2020 2:25 PM, Bjorn Helgaas wrote:
> PCI: Introduce pci_get_dsn()
>
> I learned this from "git log --oneline drivers/pci/pci.c". It looks
> like the other patches could benefit from this as well.
>
Sure, will follow that precedent.
> On Thu, Feb 27, 2020 at 02:36:31PM -0800, Jacob Keller wrote:
>> Several device drivers read their Device Serial Number from the PCIe
>> extended config space.
>>
>> Introduce a new helper function, pci_get_dsn, which will read the
>> eight bytes of the DSN into the provided buffer.
>
> "pci_get_dsn()"
>
>> Signed-off-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>
>> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>> Cc: Jeff Kirsher <jeffrey.t.kirsher@xxxxxxxxx>
>> Cc: QLogic-Storage-Upstream@xxxxxxxxxx
>> Cc: Michael Chan <michael.chan@xxxxxxxxxxxx>
>> ---
>> drivers/pci/pci.c | 33 +++++++++++++++++++++++++++++++++
>> include/linux/pci.h | 5 +++++
>> 2 files changed, 38 insertions(+)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index d828ca835a98..12d8101724d7 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -33,6 +33,7 @@
>> #include <linux/pci-ats.h>
>> #include <asm/setup.h>
>> #include <asm/dma.h>
>> +#include <asm/unaligned.h>
>> #include <linux/aer.h>
>> #include "pci.h"
>>
>> @@ -557,6 +558,38 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap)
>> }
>> EXPORT_SYMBOL_GPL(pci_find_ext_capability);
>>
>> +/**
>> + * pci_get_dsn - Read the 8-byte Device Serial Number
>> + * @dev: PCI device to query
>> + * @dsn: storage for the DSN. Must be at least 8 bytes
>> + *
>> + * Looks up the PCI_EXT_CAP_ID_DSN and reads the 8 bytes into the dsn storage.
>> + * Returns -EOPNOTSUPP if the device does not have the capability.
>> + */
>> +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.
>
> 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.
>
>> + 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
>>
