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SubjectRe: [PATCH -v2 1/3] PCI: introduce PCIe Device Serial Number Capability support
On 07/11/2013 04:09 PM, Bjorn Helgaas wrote:
> On Thu, Jul 11, 2013 at 3:51 AM, Don Dutile<ddutile@redhat.com> wrote:
>> On 07/11/2013 05:43 AM, Yijing Wang wrote:
>>>
>>> Introduce PCIe Ext Capability Device Serial Number support,
>>> so we can use the unique device serial number to identify
>>> the physical device. During system suspend, if the PCIe
>>> device was removed and inserted a new same device, after
>>> system resume there is no good way to identify it, maybe
>>> Device Serial Number is a good choice if device support.
>>>
>>> Signed-off-by: Yijing Wang<wangyijing@huawei.com>
>>> ---
>>> drivers/pci/pci.c | 27 +++++++++++++++++++++++++++
>>> drivers/pci/probe.c | 2 ++
>>> include/linux/pci.h | 3 +++
>>> 3 files changed, 32 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>>> index e37fea6..2e855b5 100644
>>> --- a/drivers/pci/pci.c
>>> +++ b/drivers/pci/pci.c
>>> @@ -2048,6 +2048,33 @@ void pci_free_cap_save_buffers(struct pci_dev *dev)
>>> }
>>>
>>> /**
>>> + * pci_device_serial_number - get device serial number
>>> + * @dev: the PCI device
>>> + *
>>> + * return the device serial number if device support,
>>> + * otherwise return 0.
>>> + */
>>> +u64 pci_device_serial_number(struct pci_dev *dev)
>>
>> See comment below:
>> void pci_device_serial_number(struct pci_dev *dev)
>>
>>
>>> +{
>>> + int pos;
>>> + u64 sn;
>>> + u32 lo, hi;
>>> +
>>> + if (!pci_is_pcie(dev))
>>> + return 0;
>>> +
>>
>> See comment below:
>> if (!pci_is_pcie(dev)) {
>> dev->sn = 0;
>> return;
>>
>> }
>>>
>>> + pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DSN);
>>> + if (!pos)
>>> + return 0;
>>> +
>>> + pci_read_config_dword(dev, pos + 4,&lo);
>>> + pci_read_config_dword(dev, pos + 8,&hi);
>>> + sn = ((u64)hi<< 32) | lo;
>>
>> See comment below:
>> dev->sn = ((u64)hi<< 32) | lo;
>> return;
>>
>>> + return sn;
>>> +}
>>> +EXPORT_SYMBOL(pci_device_serial_number);
>>> +
>>> +/**
>>> * pci_configure_ari - enable or disable ARI forwarding
>>> * @dev: the PCI device
>>> *
>>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>>> index 46ada5c..c4c1a2b 100644
>>> --- a/drivers/pci/probe.c
>>> +++ b/drivers/pci/probe.c
>>> @@ -1322,6 +1322,8 @@ static void pci_init_capabilities(struct pci_dev
>>> *dev)
>>> /* Power Management */
>>> pci_pm_init(dev);
>>>
>>> + dev->sn = pci_device_serial_number(dev);
>>> +
>>
>> Finally, 'the comment below':
>> I know you were following Bjorn's suggestion, which I thought
>> was an improvement, but why not do above assignment in
>> pci_device_serial_number() ?
>> See above....
>
> pci_device_serial_number() would then have the side-effect of saving
> the result somewhere, and callers would have to know where to look.
Ah, like so many other features of a PCI device? -- what are all those
flags/status bits in pdev for ??? ;-)

> Personally, I think it's simpler to return the serial number directly
> and avoid the side-effect, but maybe this is just bike-shedding.
>
What struck me about rtning a value is in pci_init_capabilities(),
it was the only function with a rtn value that had to be put into a pci_dev
struct element,
while all the others stored their related capabilities in the pdev, or other struct
related to it.

So, maybe there should be a "pci_device_serial_number_init()" function
which does the storage in the pdev struct, and another (wrapper,
dare I shoot myself, inline) that is "pci_device_serial_number()" that returns
the value of the pdev's sn element, if another module or other core component
want to get it. .... and do that in a future patch... :-/

> As long as we are bike-shedding, I'd just drop "sn" and do:
>
> return ((u64)hi<< 32) | lo;
>
> And of course, you need spaces before "&hi" and "&lo" in the
> pci_read_config_dword() calls.



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