linux-kernel - Re: [PATCH v2] PCI: altera: Retrain link in rootport mode only

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Date:   Wed, 24 Aug 2016 15:07:52 +0800
From:   Ley Foon Tan <lftan@...era.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v2] PCI: altera: Retrain link in rootport mode only

On Mon, Aug 22, 2016 at 11:47 PM, Bjorn Helgaas <helgaas@...nel.org> wrote:
> On Fri, Aug 19, 2016 at 04:24:38PM +0800, Ley Foon Tan wrote:
>> Altera PCIe IP can be configured as rootport or device and they might have
>> same vendor ID. It will cause the system hang issue if Altera PCIe is in
>> endpoint mode and work with other PCIe rootport that from other vendors.
>> So, add the rootport mode checking in link retrain fixup function.
>>
>> Signed-off-by: Ley Foon Tan <lftan@...era.com>
>> ---
>> v2: change to check PCIe type is PCI_EXP_TYPE_ROOT_PORT
>> ---
>>  drivers/pci/host/pcie-altera.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/pci/host/pcie-altera.c b/drivers/pci/host/pcie-altera.c
>> index 58eef99..33b6968 100644
>> --- a/drivers/pci/host/pcie-altera.c
>> +++ b/drivers/pci/host/pcie-altera.c
>> @@ -139,6 +139,9 @@ static void altera_pcie_retrain(struct pci_dev *dev)
>>       u16 linkcap, linkstat;
>>       struct altera_pcie *pcie = dev->bus->sysdata;
>>
>> +     if (pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT)
>> +             return;
>> +
>>       if (!altera_pcie_link_is_up(pcie))
>>               return;
>
> Instead of making this a PCI fixup, can you make an
> altera_pcie_host_init() function, call it from altera_pcie_probe(),
> and do the link retrain there?  Then you wouldn't need to worry about
> whether this is a Root Port or an Endpoint, plus it would make the
> altera driver structure more like the other drivers.
>
> You would call altera_pcie_host_init() before pci_scan_root_bus(), so
> you wouldn't have a pci_dev yet, so you wouldn't be able to use
> pcie_capability_set_word() to set the PCI_EXP_LNKCTL_RL bit.  But I
> assume there's some device-dependent way to access it using
> cra_writel()?
We can't use cra_write() to set PCI_EXP_LNKCTL_RL bit. We can use
pci_bus_find_capability() and pci_bus_read_config_word() with struct
pci_bus instead.
But this only can be called after pci_scan_root_bus(). Found
iproc_pcie_check_link() have similar implementation.
Tested this method is working. Do you think it is okay? If yes, then I
will send in next revision.

Thanks.

Regards
Ley Foon