On 2013/10/11 14:53, Gavin Shan wrote:
> On Fri, Oct 11, 2013 at 02:33:58PM +0800, Yijing Wang wrote:
>> On 2013/10/11 14:16, Gavin Shan wrote:
>>> On Fri, Oct 11, 2013 at 04:49:56PM +1100, Benjamin Herrenschmidt wrote:
>>>> On Fri, 2013-09-06 at 14:30 -0600, Bjorn Helgaas wrote:
>>>>> On Thu, Sep 05, 2013 at 03:55:27PM +0800, Yijing Wang wrote:
>
> .../...
>
>>>>>> Use pci_is_pcie() to simplify code.
>>>>>> diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
>>>>>> index 55593ee..6ebbe54 100644
>>>>>> --- a/arch/powerpc/kernel/eeh.c
>>>>>> +++ b/arch/powerpc/kernel/eeh.c
>>>>>> @@ -189,8 +189,7 @@ static size_t eeh_gather_pci_data(struct eeh_dev
>>>>>> *edev, char * buf, size_t len)
>>>>>> }
>>>>>>
>>>>>> /* If PCI-E capable, dump PCI-E cap 10, and the AER */
>>>>>> - cap = pci_find_capability(dev, PCI_CAP_ID_EXP);
>>>>>> - if (cap) {
>>>>>> + if (pci_is_pcie(dev)) {
>>>>>> n += scnprintf(buf+n, len-n, "pci-e cap10:\n");
>>>>>> printk(KERN_WARNING
>>>>>> "EEH: PCI-E capabilities and status follow:\n");
>>>>
>>>> So we remove reading of "cap", but slightly further down the code does:
>>>>
>>>> for (i=0; i<=8; i++) {
>>>> eeh_ops->read_config(dn, cap+4*i, 4, &cfg);
>>>> n += scnprintf(buf+n, len-n, "%02x:%x\n", 4*i, cfg);
>>>> printk(KERN_WARNING "EEH: PCI-E %02x: %08x\n", i, cfg);
>>>> }
>>>>
>>>> Which actually *uses* the value of "cap" ... oops :-)
>>>>
>>>
>>> It's my fault and I should have looked into the changes more closely.
>>> How about changing it like this:
>>>
>>> cap = pci_is_pcie(dev) ? pci_pcie_cap(dev) :
>>> pci_find_capability(dev, PCI_CAP_ID_EXP);
>>> if (cap) {
>>> ...
>>> }
>>>
>>> It would save some PCI-CFG access cycles for most cases :-)
>>
>> Hi Gavin, it's not your fault, it's my fault. :)
>>
>> Because pci_pcie_cap(dev) == dev->pcie_cap == pci_find_capability(dev,
>> PCI_CAP_ID_EXP);
>>
>> so I think it's ok to use dev->pcie_cap instead of stale "cap".
>>
>
> Yijing, There has one exception: dev->pcie_cap isn't updated yet.
In my idea, dev->pcie_cap(here is pci_dev->pcie_cap) will update in
set_pcie_port_type() function,
and this function always be called after allocate pci device. We get pci_dev by
eeh_dev_to_pci_dev(),
I think pci_dev has been initialized completely.
> This function has possibility to be invoked before that. However,
> we don't have the binding (eeh device <-> PCI device) for the case.
> So the piece of code shouldn't be running
In PCI core, I knew
pci_scan_device()
pci_setup_device()
set_pcie_port_type()
pci_dev->pcie_cap = pci_find_capability(pdev, PCI_CAP_ID_EXP);
In powerpc, I also found
of_scan_pci_dev()
of_create_pci_dev()
set_pcie_port_type()
pci_dev->pcie_cap = pci_find_capability(pdev, PCI_CAP_ID_EXP);
>
> However, it's a bit safer to have pci_find_capability(dev, PCI_CAP_ID_EXP)
> as well even though we needn't it for 99.9% cases if you agree :-)
I agree, this function is not the performance bottleneck,
safety is more important. :)
So if Bjorn and Benjamin think it's not safe, it's ok to drop it. :)
Thanks!
Yijing.
>
> Thanks,
> Gavin
>
>
> .
>
--
Thanks!
Yijing
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