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From:   AceLan Kao <acelan.kao@canonical.com>
Date:   Thu, 9 Aug 2018 14:29:31 +0800
Message-ID: <CAFv23QmqwgS-wcO+RWMKb9Ejo4zjqmWTvKorar1uJuZzfJ1iHw@mail.gmail.com>
Subject: Re: [PATCH] PCI: Fix calculation of bridge window's size
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     Bjorn Helgaas <bhelgaas@google.com>, linux-pci@vger.kernel.org,
        "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>
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Hi Bjorn,

Here is the public bug.
https://bugzilla.kernel.org/show_bug.cgi?id=200769

Best regards,
AceLan Kao.

2018-08-09 2:00 GMT+08:00 Bjorn Helgaas <helgaas@kernel.org>:
> On Wed, Aug 08, 2018 at 01:48:37PM +0800, AceLan Kao wrote:
>> There are some 0 resource size pci devices, and it leads to the
>> accumulator fails to maintain the correct value.
>> It results in a strange issue on my machine that xhci_hcd failed to init.
>>    [    2.437278] xhci_hcd 0000:05:00.0: init 0000:05:00.0 fail, -16
>>    [    2.437300] xhci_hcd: probe of 0000:05:00.0 failed with error -16
>
> I don't think it's possible for a PCI device to have a BAR of zero
> size.  Bits 0-3 of memory BARs are read-only, leading to a minimum BAR
> size of 16 bytes; similarly, bits 0-1 of I/O BARs are read-only,
> giving a minimum size of 4 ports.
>
> My guess is that if you have a pci_dev with a resource that looks like
> it's valid but has zero size, that resource came from OF or device
> tree.  If that's the case, I'd say we should fix the OF or DT parsing
> code to reject those resources.  If we do that, we shouldn't need the
> patch below.
>
> Can you open a bugzilla.kernel.org report and attach the complete
> dmesg log leading up to this, as well as the "sudo lspci -vv" output
> for this device?  It should have clues about how we got here.
>
>> To fix this, check if the resource size equals to 0, doesn't increase size.
>>
>> Fixes: c9c75143a596 ("PCI: Fix calculation of bridge window's size and alignment")
>> CC: stable@vger.kernel.org # 4.14+
>>
>> Signed-off-by: AceLan Kao <acelan.kao@canonical.com>
>> ---
>>  drivers/pci/setup-bus.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
>> index 79b1824e83b4..ae05dde8c6e3 100644
>> --- a/drivers/pci/setup-bus.c
>> +++ b/drivers/pci/setup-bus.c
>> @@ -1061,7 +1061,8 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
>>                               r->flags = 0;
>>                               continue;
>>                       }
>> -                     size += max(r_size, align);
>> +                     if (r_size != 0)
>> +                             size += max(r_size, align);
>>                       /* Exclude ranges with size > align from
>>                          calculation of the alignment. */
>>                       if (r_size <= align)
>> --
>> 2.17.1
>>