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

[Yijing Wang <wangyijing@huawei.com>]

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.

> 
> Thanks,
> Ethan
> 
> 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