Re: [PATCH v4 2/3] PCI: Enable PCIe Relaxed Ordering if supported

[Alexander Duyck]

On Thu, Jun 15, 2017 at 6:10 PM, Ding Tianhong <dingtianhong@xxxxxxxxxx> wrote:
>
>
> On 2017/6/13 5:28, Alexander Duyck wrote:
>> On Mon, Jun 12, 2017 at 4:05 AM, Ding Tianhong <dingtianhong@xxxxxxxxxx> wrote:
> ...
>>>  /**
>>> + * pcie_clear_relaxed_ordering - clear PCI Express relaxed ordering bit
>>> + * @dev: PCI device to query
>>> + *
>>> + * If possible clear relaxed ordering
>>> + */
>>> +int pcie_clear_relaxed_ordering(struct pci_dev *dev)
>>> +{
>>> +       return pcie_capability_clear_word(dev, PCI_EXP_DEVCTL,
>>> +                                         PCI_EXP_DEVCTL_RELAX_EN);
>>> +}
>>> +EXPORT_SYMBOL(pcie_clear_relaxed_ordering);
>>> +
>>> +/**
>>> + * pcie_relaxed_ordering_supported - Probe for PCIe relexed ordering support
>>> + * @dev: PCI device to query
>>> + *
>>> + * Returns true if the device support relaxed ordering attribute.
>>> + */
>>> +bool pcie_relaxed_ordering_supported(struct pci_dev *dev)
>>> +{
>>> +       bool ro_supported = false;
>>> +       u16 v;
>>> +
>>> +       pcie_capability_read_word(dev, PCI_EXP_DEVCTL, &v);
>>> +       if ((v & PCI_EXP_DEVCTL_RELAX_EN) >> 4)
>>> +               ro_supported = true;
>>
>> Instead of "return ro_supported" why not just "return !!(v &
>> PCIE_EXP_DEVCTL_RELAX_EN)"? You can cut out the extra steps and save
>> yourself some extra steps this way since the shift by 4 shouldn't even
>> really be needed since you are just testing for a bit anyway.
>>
>
> OK.
>
>>> +
>>> +       return ro_supported;
>>> +}
>>> +EXPORT_SYMBOL(pcie_relaxed_ordering_supported);
>>> +
>>> +/**
>>>   * pcie_get_minimum_link - determine minimum link settings of a PCI device
>>>   * @dev: PCI device to query
>>>   * @speed: storage for minimum speed
>>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>>> index 19c8950..ed1f717 100644
>>> --- a/drivers/pci/probe.c
>>> +++ b/drivers/pci/probe.c
>>> @@ -1701,6 +1701,46 @@ static void pci_configure_extended_tags(struct pci_dev *dev)
>>>                                          PCI_EXP_DEVCTL_EXT_TAG);
>>>  }
>>>
>>> +/**
>>> + * pci_dev_should_disable_relaxed_ordering - check if the PCI device
>>> + * should disable the relaxed ordering attribute.
>>> + * @dev: PCI device
>>> + *
>>> + * Return true if any of the PCI devices above us do not support
>>> + * relaxed ordering.
>>> + */
>>> +static bool pci_dev_should_disable_relaxed_ordering(struct pci_dev *dev)
>>> +{
>>> +       bool ro_disabled = false;
>>> +
>>> +       while (dev) {
>>> +               if (dev->dev_flags & PCI_DEV_FLAGS_NO_RELAXED_ORDERING) {
>>> +                       ro_disabled = true;
>>> +                       break;
>>> +               }
>>> +               dev = dev->bus->self;
>>> +       }
>>> +
>>> +       return ro_disabled;
>>
>> Same thing here. I would suggest just returning either true or false,
>> and drop the ro_disabled value. It will return the lines of code and
>> make things a bit bit more direct.
>>
>
> OK.
>
>>> +}
>>> +
>>> +static void pci_configure_relaxed_ordering(struct pci_dev *dev)
>>> +{
>>> +       struct pci_dev *bridge = pci_upstream_bridge(dev);
>>> +
>>> +       if (!pci_is_pcie(dev) || !bridge || !pci_is_pcie(bridge))
>>> +               return;
>>
>> The pci_is_pcie check is actually redundant based on the
>> pcie_relaxed_ordering_supported check using pcie_capability_read_word.
>>
>
> Yes, pcie_capability_read_word already check it, thanks.
>
>
>> Also I am not sure what the point is of the pci_upstream_bridge()
>> check is, it seems like you should be able to catch all the same stuff
>> in your pci_dev_should_disable_relaxed_ordering() call. Though it did
>> give me a thought. I don't think we can alter this for a VF, so you
>> might want to add a check for dev->is_virtfn to the list of checks and
>> if it is a virtual function just return since I don't think there are
>> any VFs that would let you alter this bit anyway.
>>
> If the upstream device is null, does it mean that it is in a guest OS device? maybe I miss something.
> also I will check the dev->is_virtfn to avoid trying to change the configuration space for VF.

Yes, usually the upstream device is NULL in guest setups where all the
devices are hung off of a single PCI bus.

> Another question: Because it looks like that maybe the Casey is too busy these days, should we
> delay the modification of the cxgb4 and instead to update the ixgbe? what do you think about it. :)

I would still submit the cxgb4 changes with the one change we have
made. It should work as is. We can just leave any follow-up work to
Casey in terms of enabling the peer-to-peer mode if the bits related
to relaxed ordering are cleared.

> Thanks.
> Ding
>
>>> +       /* If the releaxed ordering enable bit is not set, do nothing. */
>>> +       if (!pcie_relaxed_ordering_supported(dev))
>>> +               return;
>>> +
>>> +       if (pci_dev_should_disable_relaxed_ordering(dev)) {
>>> +               pcie_clear_relaxed_ordering(dev);
>>> +               dev_info(&dev->dev, "Disable Relaxed Ordering\n");
>>> +       }
>>> +}
>>> +
>>>  static void pci_configure_device(struct pci_dev *dev)
>>>  {
>>>         struct hotplug_params hpp;
>>> @@ -1708,6 +1748,7 @@ static void pci_configure_device(struct pci_dev *dev)
>>>
>>>         pci_configure_mps(dev);
>>>         pci_configure_extended_tags(dev);
>>> +       pci_configure_relaxed_ordering(dev);
>>>
>>>         memset(&hpp, 0, sizeof(hpp));
>>>         ret = pci_get_hp_params(dev, &hpp);
>>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>>> index e1e8428..9870781 100644
>>> --- a/include/linux/pci.h
>>> +++ b/include/linux/pci.h
>>> @@ -1105,6 +1105,8 @@ int __pci_enable_wake(struct pci_dev *dev, pci_power_t state,
>>>  void pci_pme_wakeup_bus(struct pci_bus *bus);
>>>  void pci_d3cold_enable(struct pci_dev *dev);
>>>  void pci_d3cold_disable(struct pci_dev *dev);
>>> +int pcie_clear_relaxed_ordering(struct pci_dev *dev);
>>> +bool pcie_relaxed_ordering_supported(struct pci_dev *dev);
>>>
>>>  static inline int pci_enable_wake(struct pci_dev *dev, pci_power_t state,
>>>                                   bool enable)
>>> --
>>> 1.9.0
>>>
>>>
>>
>> .
>>
>