linux-kernel - Re: [PATCH v3 2/3] PCI: Enable PCIe Relaxed Ordering if supported

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Message-ID: <cf91605b-2c9d-150f-ad1d-a8cc17e0a1ee@huawei.com>
Date:   Fri, 9 Jun 2017 17:13:37 +0800
From:   Ding Tianhong <dingtianhong@...wei.com>
To:     John Garry <john.garry@...wei.com>, <leedom@...lsio.com>,
        <ashok.raj@...el.com>, <helgaas@...nel.org>, <werner@...lsio.com>,
        <ganeshgr@...lsio.com>, <asit.k.mallick@...el.com>,
        <patrick.j.cramer@...el.com>, <Suravee.Suthikulpanit@....com>,
        <Bob.Shaw@....com>, <l.stach@...gutronix.de>, <amira@...lanox.com>,
        <gabriele.paoloni@...wei.com>, <David.Laight@...lab.com>,
        <jeffrey.t.kirsher@...el.com>, <catalin.marinas@....com>,
        <will.deacon@....com>, <mark.rutland@....com>,
        <robin.murphy@....com>, <davem@...emloft.net>,
        <alexander.duyck@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>, <netdev@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH v3 2/3] PCI: Enable PCIe Relaxed Ordering if supported


Hi John:

Thanks for the reviewing, I will fix it in next version.

Ding

On 2017/6/8 1:55, John Garry wrote:
> On 07/06/2017 10:16, Ding Tianhong wrote:
> 
> Hi Ding,
> 
> A few general style comments:
> 
>> 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 PCIe device didn't enable the relaxed ordering attribute default,
>> we should not do anything in the PCIe configuration, otherwise we
>> should check if any of the devices above us do not support relaxed
>> ordering by the PCI_DEV_FLAGS_NO_RELAXED_ORDERING flag, then base on
>> the result if we get a return that indicate that the relaxed ordering
>> is not supported we should update our device to disable relaxed ordering
>> in configuration space. If the device above us doesn't exist or isn't
>> the PCIe device, we shouldn't do anything and skip updating relaxed ordering
>> because we are probably running in a guest.
> 
> A guest machine/environment
> 
>>
>> Signed-off-by: Ding Tianhong <dingtianhong@...wei.com>
>> ---
>>  drivers/pci/pci.c   | 29 +++++++++++++++++++++++++++++
>>  drivers/pci/probe.c | 43 +++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/pci.h |  2 ++
>>  3 files changed, 74 insertions(+)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index b01bd5b..3d42b38 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -4878,6 +4878,35 @@ int pcie_set_mps(struct pci_dev *dev, int mps)
>>  EXPORT_SYMBOL(pcie_set_mps);
>>
>>  /**
>> + * 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
> 
> s/relexed/relaxed/
> 
> Check what on relaxed ordering bit?
> 
> And the function name is inconsistent with this discription.
> 
>> + * @dev: PCI device to query
>> + *
>> + * Returns true if relaxed ordering is been set
> 
> If you want to return true/false, then use !!, below in the function
> 
>> + */
>> +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_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..0c94c80 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -1701,6 +1701,48 @@ static void pci_configure_extended_tags(struct pci_dev *dev)
>>                       PCI_EXP_DEVCTL_EXT_TAG);
>>  }
>>
>> +/**
>> + * pci_dev_disable_relaxed_ordering - check if the PCI device
>> + * should disable the relaxed ordering attribute.
> 
> I think that we need a more accurate description. I know some people think a function which just "checks" is vague.
> 
>> + * @dev: PCI device
>> + *
>> + * Return true if any of the PCI devices above us do not support
>> + * relaxed ordering.
>> + */
>> +static int pci_dev_disable_relaxed_ordering(struct pci_dev *dev)
> 
> The function name implies an action - disabling - but this function does nothing except return a value
> 
>> +{
>> +    int ro_disabled = 0;
>> +
>> +    while(dev) {
> 
> Did you run checkpatch?
> 
>> +        if (dev->dev_flags & PCI_DEV_FLAGS_NO_RELAXED_ORDERING) {
>> +            ro_disabled = 1;
> 
> just return true, and return false at the bottom, so you can do away with ro_disabled (which is not a bool)
> 
>> +            break;
>> +        }
>> +        dev = dev->bus->self;
>> +    }
>> +
>> +    return ro_disabled;
>> +}
>> +
>> +static void pci_configure_relaxed_ordering(struct pci_dev *dev)
>> +{
>> +    struct pci_dev *bridge = pci_upstream_bridge(dev);
>> +    int origin_ero;
> 
> You don't need this variable
> 
>> +
>> +    if (!pci_is_pcie(dev) || !bridge || !pci_is_pcie(bridge))
>> +        return;
>> +
>> +    origin_ero = pcie_get_relaxed_ordering(dev);
>> +    /* If the releaxed ordering enable bit is not set, do nothing. */
>> +    if (!origin_ero)
>> +        return;
>> +
>> +    if (pci_dev_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 +1750,7 @@ 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..299d2f3 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);
>> +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)
>>
> 
> 
> 
> .
>