[PATCH v1] PCI: Make PCI_SCAN_ALL_PCIE_DEVS work for Root as well as Downstream Ports

[Christian Zigotzky]

Hi Bjorn,

Sorry for my late answer. The X1000 boots and works since yesterday. I think the following patch solved the issue: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c591c2e36ccc9a08f265841d2fd68e35327ab3c4

Cheers,
Christian

Sent from my iPhone

> On 10. Feb 2018, at 16:43, Bjorn Helgaas <helgaas at kernel.org> wrote:
> 
>> On Sat, Feb 10, 2018 at 09:05:40AM +0100, Christian Zigotzky wrote:
>> Hi All,
>> 
>> The AmigaOne X1000 doesn’t boot anymore since the PCI updates. I
>> have seen, that the PCI updates are different to the updates below.
>> The code below works but the latest not. Is there a problem with the
>> latest PCI updates currently?
> 
> I'm not aware of a problem, and it *looks* like the patch below is in
> Linus' tree (I'm looking at 9a61df9e5f74 ("Merge tag 'kbuild-v4.16-2'
> of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild")).
> 
> I assume you're still booting with "pci=pcie_scan_all", since I don't
> think we ever got a quirk to set PCI_SCAN_ALL_PCIE_DEVS automatically.
> 
> If AmigaOne X1000 doesn't boot with "pci=pcie_scan_all", can you diff
> the working only_one_child() with the current upstream?  I compared
> the version in my pci/enumeration branch with what's upstream, and
> they're identical.  So maybe the original patch I applied was wrong?
> 
> If you have a patch that works, can you post it and maybe I can sort
> out what's different?
> 
>> On 2. Dec 2017, at 20:18, Bjorn Helgaas <helgaas at kernel.org> wrote:
>> 
>> On Fri, Dec 01, 2017 at 06:27:10PM -0600, Bjorn Helgaas wrote:
>> From: Bjorn Helgaas <bhelgaas at google.com>
>> 
>> PCIe Downstream Ports normally have only a Device 0 below them.  To
>> optimize enumeration, we don't scan for other devices *unless* the
>> PCI_SCAN_ALL_PCIE_DEVS flag is set by set by quirks or the
>> "pci=pcie_scan_all" kernel parameter.
>> 
>> Previously PCI_SCAN_ALL_PCIE_DEVS only affected scanning below Switch
>> Downstream Ports, not Root Ports.
>> 
>> But the "Nemo" system, also known as the AmigaOne X1000, has a PA Semi Root
>> Port whose link leads to an AMD/ATI SB600 South Bridge.  The Root Port is a
>> PCIe device, of course, but the SB600 contains only conventional PCI
>> devices with no visible PCIe port.
>> 
>> Simplify and restructure only_one_child() so that we scan for all possible
>> devices below Root Ports as well as Switch Downstream Ports when
>> PCI_SCAN_ALL_PCIE_DEVS is set.
>> 
>> This is enough to make Nemo work with "pci=pcie_scan_all".  We would also
>> like to add a quirk to set PCI_SCAN_ALL_PCIE_DEVS automatically on Nemo so
>> users wouldn't have to use the "pci=pcie_scan_all" parameter, but we don't
>> have that yet.
>> 
>> Link: https://lkml.kernel.org/r/CAErSpo55Q8Q=5p6_+uu7ahnw+53ibVDNRXxrzRV9QnUr_9EUfw@mail.gmail.com
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=198057
>> Reported-and-Tested-by: Christian Zigotzky <chzigotzky at xenosoft.de>
>> Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
>> 
>> Applied to pci/enumeration for v4.16.
>> 
>> ---
>> drivers/pci/probe.c |   25 +++++++++++++++----------
>> 1 file changed, 15 insertions(+), 10 deletions(-)
>> 
>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> index 14e0ea1ff38b..303c0cb0550c 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -2215,22 +2215,27 @@ static unsigned next_fn(struct pci_bus *bus, struct pci_dev *dev, unsigned fn)
>> 
>> static int only_one_child(struct pci_bus *bus)
>> {
>> -    struct pci_dev *parent = bus->self;
>> +    struct pci_dev *bridge = bus->self;
>> 
>> -    if (!parent || !pci_is_pcie(parent))
>> +    /*
>> +     * Systems with unusual topologies set PCI_SCAN_ALL_PCIE_DEVS so
>> +     * we scan for all possible devices, not just Device 0.
>> +     */
>> +    if (pci_has_flag(PCI_SCAN_ALL_PCIE_DEVS))
>>       return 0;
>> -    if (pci_pcie_type(parent) == PCI_EXP_TYPE_ROOT_PORT)
>> -        return 1;
>> 
>>   /*
>> -     * PCIe downstream ports are bridges that normally lead to only a
>> -     * device 0, but if PCI_SCAN_ALL_PCIE_DEVS is set, scan all
>> -     * possible devices, not just device 0.  See PCIe spec r3.0,
>> -     * sec 7.3.1.
>> +     * A PCIe Downstream Port normally leads to a Link with only Device
>> +     * 0 on it (PCIe spec r3.1, sec 7.3.1).  As an optimization, scan
>> +     * only for Device 0 in that situation.
>> +     *
>> +     * Checking has_secondary_link is a hack to identify Downstream
>> +     * Ports because sometimes Switches are configured such that the
>> +     * PCIe Port Type labels are backwards.
>>    */
>> -    if (parent->has_secondary_link &&
>> -        !pci_has_flag(PCI_SCAN_ALL_PCIE_DEVS))
>> +    if (bridge && pci_is_pcie(bridge) && bridge->has_secondary_link)
>>       return 1;
>> +
>>   return 0;
>> }
>> 
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