Re: [PATCH v2 2/3] PCI: Enable PCIe Relaxed Ordering if supported

[Alexander Duyck]

On Mon, Jun 5, 2017 at 6:33 AM, Ding Tianhong <dingtianhong@xxxxxxxxxx> wrote:
>
>
> On 2017/6/4 2:19, Alexander Duyck wrote:
>> On Fri, Jun 2, 2017 at 9:04 PM, Ding Tianhong <dingtianhong@xxxxxxxxxx> wrote:
>>> The PCIe Device Control Register use the bit 4 to indicate that
>>> whether the device is permitted to enable relaxed ordering or not.
>>> But relaxed ordering is not safe for some platform which could only
>>> use strong write ordering, so devices are allowed (but not required)
>>> to enable relaxed ordering bit by default.
>>>
>>> If a platform support relaxed ordering but does not enable it by
>>> default, enable it in the PCIe configuration. This allows some device
>>> to send TLPs with the relaxed ordering attributes set, which may
>>> improve the performance.
>>>
>>> Signed-off-by: Ding Tianhong <dingtianhong@xxxxxxxxxx>
>>> ---
>>>  drivers/pci/pci.c   | 42 ++++++++++++++++++++++++++++++++++++++++++
>>>  drivers/pci/probe.c | 11 +++++++++++
>>>  include/linux/pci.h |  3 +++
>>>  3 files changed, 56 insertions(+)
>>>
>>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>>> index b01bd5b..f57a374 100644
>>> --- a/drivers/pci/pci.c
>>> +++ b/drivers/pci/pci.c
>>> @@ -4878,6 +4878,48 @@ int pcie_set_mps(struct pci_dev *dev, int mps)
>>>  EXPORT_SYMBOL(pcie_set_mps);
>>>
>>>  /**
>>> + * pcie_set_relaxed_ordering - set PCI Express relexed ordering bit
>>> + * @dev: PCI device to query
>>> + *
>>> + * If possible sets relaxed ordering
>>> + */
>>> +int pcie_set_relaxed_ordering(struct pci_dev *dev)
>>> +{
>>> +       return pcie_capability_set_word(dev, PCI_EXP_DEVCTL, PCI_EXP_DEVCTL_RELAX_EN);
>>> +}
>>> +EXPORT_SYMBOL(pcie_set_relaxed_ordering);
>>> +
>>> +/**
>>> + * pcie_clear_relaxed_ordering - clear PCI Express relexed 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_get_relaxed_ordering - check PCI Express relexed ordering bit
>>> + * @dev: PCI device to query
>>> + *
>>> + * Returns true if relaxed ordering is been set
>>> + */
>>> +int pcie_get_relaxed_ordering(struct pci_dev *dev)
>>> +{
>>> +       u16 v;
>>> +
>>> +       pcie_capability_read_word(dev, PCI_EXP_DEVCTL, &v);
>>> +
>>> +       return (v & PCI_EXP_DEVCTL_RELAX_EN) >> 4;
>>> +}
>>> +EXPORT_SYMBOL(pcie_get_relaxed_ordering);
>>> +
>>> +/**
>>> + * pcie_set_mps - set PCI Express maximum payload size
>>> +/**
>>>   * 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..aeb22b5 100644
>>> --- a/drivers/pci/probe.c
>>> +++ b/drivers/pci/probe.c
>>> @@ -1701,6 +1701,16 @@ static void pci_configure_extended_tags(struct pci_dev *dev)
>>>                                          PCI_EXP_DEVCTL_EXT_TAG);
>>>  }
>>>
>>> +static void pci_configure_relaxed_ordering(struct pci_dev *dev)
>>> +{
>>> +       int ret;
>>> +
>>> +       if (dev && (dev->dev_flags & PCI_DEV_FLAGS_NO_RELAXED_ORDERING))
>>
>> So there is a minor issue here. The problem is this is only trying to
>> modify relaxed ordering for the device itself. That isn't what we
>> want. What we want is to modify it on all of the upstream port
>> interfaces where there is something the path to the root complex that
>> has an issue. So if the root complex has to set the
>> NO_RELAXED_ORDERING flag on a root port, all of the interfaces below
>> it that would be pushing traffic toward it should not have the relaxed
>> ordering bit set.
>>
>> Also I am pretty sure this is a PCIe capability, not a PCI capability.
>> You probably need to make sure you code is making this distinction
>> which I don't know if it currently is. If you need an example of the
>> kind of checks I am suggesting just take a look at
>> pcie_configure_mps(). It is verifying the function is PCIe before
>> attempting to make any updates. In your case you will probably also
>> need to make sure there is a bus for you to walk up the chain of.
>> Otherwise this shouldn't apply.
>>
>>
>>> +               pcie_set_relaxed_ordering(dev);
>>> +       else
>>> +               pcie_clear_relaxed_ordering(dev);
>>> +}
>>
>> Also I am not a fan of the way this is handled currently. If you don't
>> have relaxed ordering set then you don't need to do anything else, if
>> you do have it set but there is no bus to walk up you shouldn't change
>> it, and if there is a bus to walk up and you find that the root
>> complex on that bus has the NO_RELAXED_ORDERING set you should clear
>> it. Right now this code seems to be enabling relaxed ordering if the
>> NO_RELAXED_ORDERING flag is set.
>>
>
> Hi Alexander:
>
> I reconsidered your suggestion and found I miss something here,
> decide to modify the configure police as your solution, I think
> it is close to our goal.
>
> Thanks
> Ding
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 19c8950..68dee05 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1701,6 +1701,45 @@ static void pci_configure_extended_tags(struct pci_dev *dev)
>                                          PCI_EXP_DEVCTL_EXT_TAG);
>  }
>
> +static int pcie_clearing_relaxed_ordering(struct pci_dev *dev, void *data)
> +{
> + int origin_ero;
> +
> + if (!pci_is_pcie(dev))
> +         return 0;
> +
> + origin_ero = pcie_get_relaxed_ordering(dev);
> +
> + /* If the releaxed ordering enable bit is not set, do nothing. */
> + if (!origin_ero)
> +         return 0;
> +
> + pcie_clear_relaxed_ordering(dev);
> +
> + dev_info(&dev->dev, "Disable Relaxed Ordering\n");
> +
> + return 0;
> +}
> +
> +static void pci_configure_relaxed_ordering(struct pci_dev *dev)
> +{
> + int origin_ero;
> +
> + if (!pci_is_pcie(dev))
> +         return;
> +
> + origin_ero = pcie_get_relaxed_ordering(dev);
> + /* If the releaxed ordering enable bit is not set, do nothing. */
> + if (!origin_ero)
> +         return;
> +
> + if (dev->dev_flags & PCI_DEV_FLAGS_NO_RELAXED_ORDERING) {
> +         pcie_clear_relaxed_ordering(dev);
> +         pci_walk_bus(dev->bus, pcie_clearing_relaxed_ordering, NULL);
> +         dev_info(&dev->dev, "Disable Relaxed Ordering\n");
> + }
> +}
> +

This is kind of backwards from what I was thinking. Basically what I
would like to see is at probe time we should work our way up the PCIe
buses checking to see if any device has
PCI_DEV_FLAGS_NO_RELAXED_ORDERING set. The assumption is if we can't
use relaxed ordering with the downstream facing port we probably
shouldn't be enabling it on our upstream facing port. We don't want to
be writing to other devices and such since we don't know what they
need, we will only know what our device needs and if the root complex
reports that it can't support relaxed ordering we should disable it
for the device we are initializing and move on.

You might use pcie_get_minimum_link as an example of what I am
thinking. Basically what we should do is add a function that will
return true if any of the devices above us do not support relaxed
ordering, otherwise return false. Then based on that result if we get
a return that indicates that relaxed ordering is not supported we
should update our device to disable relaxed ordering. If the device
above us doesn't exist, or isn't PCIe we should just exit and skip
updating relaxed ordering since we are probably running in a guest.

>  static void pci_configure_device(struct pci_dev *dev)
>  {
>         struct hotplug_params hpp;
> @@ -1708,6 +1747,7 @@ 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
>
>
>
>>> +
>>>  static void pci_configure_device(struct pci_dev *dev)
>>>  {
>>>         struct hotplug_params hpp;
>>> @@ -1708,6 +1718,7 @@ 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..84bd6af 100644
>>> --- a/include/linux/pci.h
>>> +++ b/include/linux/pci.h
>>> @@ -1105,6 +1105,9 @@ 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_set_relaxed_ordering(struct pci_dev *dev);
>>> +int pcie_clear_relaxed_ordering(struct pci_dev *dev);
>>> +int pcie_get_relaxed_ordering(struct pci_dev *dev);
>>>
>>>  static inline int pci_enable_wake(struct pci_dev *dev, pci_power_t state,
>>>                                   bool enable)
>>> --
>>> 1.9.0
>>>
>>>
>>
>> .
>>
>