Re: [PATCH] PCI: update device mps when doing pci hotplug

[Yijing Wang <wangyijing@huawei.com>]

On 2014/7/30 11:58, Ethan Zhao wrote:
> 
> 
>> 在 2014年7月30日，上午11:42，Yijing Wang <wangyijing@huawei.com> 写道：
>>
>>> On 2014/7/30 11:33, Ethan Zhao wrote:
>>> Yijing,
>>>    Seems you want to workaround platform bug in generic PCIe hotplug
>>> code, while not specific to some platforms or devices, that is not
>>> safe/fair to other vendor's platform.
>>> and the updating to MPS of device is out of PCIe specification.
>>>    So the best way is to fix within platform, at least, any platform
>>> specific way in Linux code.
>>
>> No, this is not a platform bug, and this is safe, you can refer to my last reply
>> to Alex.
> if is not a platform bug, why Didn't other platforms that can do hotplug report such issue ?
> If it was safe, is it possible that you have all other vendors verify it ? 

This issue was triggered by firmware set the device mps to 256B. It's not related to platform
hardware.

I think this is safe, because I only modified the device newly hot-added, this device is not enabled yet.

Thanks!
Yijing.


>>>
>>>> On Tue, Jul 29, 2014 at 4:17 PM, Yijing Wang <wangyijing@huawei.com> wrote:
>>>> Currently we don't update device's mps value when doing
>>>> pci device hot-add. The hot-added device's mps will be set
>>>> to default value (128B). But the upstream port device's mps
>>>> may be larger than 128B which was set by firmware during
>>>> system bootup. In this case the new added device may not
>>>> work normally. This issue was found in huawei 5885 server
>>>> and Dell R620 server. And if we run the platform with windows,
>>>> this problem is gone. This patch try to update the hot added
>>>> device mps equal to its parent mps, if device mpss < parent mps,
>>>> print warning.
>>>>
>>>> References: https://bugzilla.kernel.org/show_bug.cgi?id=60671
>>>> Reported-by: Keith Busch <keith.busch@intel.com>
>>>> Reported-by: Jordan_Hargrave@Dell.com
>>>> Reported-by: Yijing Wang <wangyijing@huawei.com>
>>>> Signed-off-by: Yijing Wang <wangyijing@huawei.com>
>>>> Cc: Jon Mason <jdmason@kudzu.us>
>>>> ---
>>>> drivers/pci/probe.c |   39 +++++++++++++++++++++++++++++++++++++++
>>>> 1 files changed, 39 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>>>> index e3cf8a2..583ca52 100644
>>>> --- a/drivers/pci/probe.c
>>>> +++ b/drivers/pci/probe.c
>>>> @@ -1613,6 +1613,44 @@ static void pcie_write_mrrs(struct pci_dev *dev)
>>>>                dev_err(&dev->dev, "MRRS was unable to be configured with a safe value.  If problems are experienced, try running with pci=pcie_bus_safe\n");
>>>> }
>>>>
>>>> +/**
>>>> + * pcie_bus_update_set - update device mps when device doing hot-add
>>>> + * @dev: PCI device to set
>>>> + *
>>>> + * After device hot add, mps will be set to default(128B), But the
>>>> + * upstream port device's mps may be larger than 128B which was set
>>>> + * by firmware during system bootup. Then we should update the device
>>>> + * mps to equal to its parent mps, Or the device can not work normally.
>>>> + */
>>>> +static void pcie_bus_update_set(struct pci_dev *dev)
>>>> +{
>>>> +       int mps, p_mps, mpss;
>>>> +       struct pci_dev *parent;
>>>> +
>>>> +       if (!pci_is_pcie(dev) || !dev->bus->self
>>>> +                       || !dev->bus->self->is_hotplug_bridge)
>>>> +               return;
>>>> +
>>>> +       parent = dev->bus->self;
>>>> +       mps = pcie_get_mps(dev);
>>>> +       p_mps = pcie_get_mps(parent);
>>>> +
>>>> +       if (mps >= p_mps)
>>>> +               return;
>>>> +
>>>> +       mpss = 128 << dev->pcie_mpss;
>>>> +       if (mpss < p_mps) {
>>>> +               dev_warn(&dev->dev, "MPSS %d smaller than upstream MPS %d\n"
>>>> +                               "If necessary, use \"pci=pcie_bus_safe\" boot parameter to avoid this problem\n",
>>>> +                               mpss, p_mps);
>>>> +               return;
>>>> +       }
>>>> +
>>>> +       pcie_write_mps(dev, p_mps);
>>>> +       dev_info(&dev->dev, "Max Payload Size set to %4d/%4d (was %4d)\n",
>>>> +                       pcie_get_mps(dev), 128 << dev->pcie_mpss, mps);
>>>> +}
>>>> +
>>>> static void pcie_bus_detect_mps(struct pci_dev *dev)
>>>> {
>>>>        struct pci_dev *bridge = dev->bus->self;
>>>> @@ -1637,6 +1675,7 @@ static int pcie_bus_configure_set(struct pci_dev *dev, void *data)
>>>>                return 0;
>>>>
>>>>        if (pcie_bus_config == PCIE_BUS_TUNE_OFF) {
>>>> +               pcie_bus_update_set(dev);
>>>>                pcie_bus_detect_mps(dev);
>>>>                return 0;
>>>>        }
>>>> --
>>>> 1.7.1
>>>>
>>>> --
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>>>
>>> .
>>
>>
>> -- 
>> Thanks!
>> Yijing
>>
> 
> .
> 


-- 
Thanks!
Yijing