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From: Bjorn Helgaas <bjorn.helgaas@gmail.com>
To: Jacob Keller <jacob.e.keller@intel.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
	linux-pci@vger.kernel.org, netdev@vger.kernel.org,
	Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
	QLogic-Storage-Upstream@cavium.com,
	Michael Chan <michael.chan@broadcom.com>
Subject: Re: [PATCH 1/5] pci: introduce pci_get_dsn
Date: Mon, 2 Mar 2020 17:39:58 -0600	[thread overview]
Message-ID: <CABhMZUXJ_Omt-+fwa4Oz-Ly=J+NM8+8Ryv-Ad1u_bgEpDRH7RQ@mail.gmail.com> (raw)
In-Reply-To: <2fa00fef-7d11-d0b6-49a0-85a2b08a144d@intel.com>

On Mon, Mar 2, 2020 at 5:24 PM Jacob Keller <jacob.e.keller@intel.com> wrote:
>
> On 3/2/2020 3:20 PM, Bjorn Helgaas wrote:
> > 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.
>
> Makes sense. So basically, convert pci_get_dsn to a simply return a u64
> instead of copying to an array, and then make callers assume that a
> value of 0 is invalid?

Yep, that's what I would do.

You might have to re-jigger the snprintfs so they still pull out the
same bytes they did before.

  reply	other threads:[~2020-03-02 23:40 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-27 22:36 [PATCH 0/5] pci: implement function to read Device Serial Number Jacob Keller
2020-02-27 22:36 ` [PATCH] ice-shared: add macro specifying max NVM offset Jacob Keller
2020-02-27 22:43   ` Jacob Keller
2020-02-27 22:36 ` [PATCH 1/5] pci: introduce pci_get_dsn Jacob Keller
2020-03-01  5:27   ` David Miller
2020-03-02 19:58     ` Jacob Keller
2020-03-02 22:25   ` Bjorn Helgaas
2020-03-02 22:33     ` Jacob Keller
2020-03-02 23:20       ` Bjorn Helgaas
2020-03-02 23:24         ` Jacob Keller
2020-03-02 23:39           ` Bjorn Helgaas [this message]
2020-03-03  2:24             ` [PATCH v2 0/6] PCI: Implement function to read Device Serial Number Jacob Keller
2020-03-03  2:25               ` [PATCH v2 1/6] PCI: Introduce pci_get_dsn Jacob Keller
2020-03-04 22:42                 ` Bjorn Helgaas
2020-03-03  2:25               ` [PATCH v2 2/6] bnxt_en: Use pci_get_dsn() Jacob Keller
2020-03-03  2:25               ` [PATCH v2 3/6] scsi: qedf: " Jacob Keller
2020-03-03  2:25               ` [PATCH v2 4/6] ice: " Jacob Keller
2020-03-03  2:25               ` [PATCH v2 5/6] ixgbe: " Jacob Keller
2020-03-03  2:25               ` [PATCH v2 6/6] nfp: " Jacob Keller
2020-03-03  3:40                 ` Jakub Kicinski
2020-03-03 17:36                   ` Jacob Keller
2020-03-04 22:28               ` [PATCH v2 0/6] PCI: Implement function to read Device Serial Number David Miller
2020-03-06  1:30               ` David Miller
2020-02-27 22:36 ` [PATCH 2/5] bnxt_en: use pci_get_dsn Jacob Keller
2020-03-02 22:25   ` Bjorn Helgaas
2020-02-27 22:36 ` [PATCH 3/5] scsi: qedf: " Jacob Keller
2020-02-27 22:36 ` [PATCH 4/5] ice: " Jacob Keller
2020-02-27 22:36 ` [PATCH 5/5] ixgbe: " Jacob Keller

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