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

[Ding Tianhong]

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.

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. :)

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
>>
>>
> 
> .
>