netdev - Re: pcie_get_minimum_link returns 0 width

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Message-ID: <CAErSpo68LaevaBG8rJD0aj+oy-cp_f2ZsQVEhXL=oUyyRiYwZw@mail.gmail.com>
Date:	Mon, 26 Aug 2013 17:57:34 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yuval Mintz <yuvalmin@...adcom.com>
Cc:	"jacob.e.keller@...el.com" <jacob.e.keller@...el.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: pcie_get_minimum_link returns 0 width

On Mon, Aug 26, 2013 at 5:36 PM, Yuval Mintz <yuvalmin@...adcom.com> wrote:
>> > Hi,
>> >
>> > I tried adding support for the newly added 'pcie_get_minimum_link' into
>> the
>> > bnx2x driver, but found out the some of my devices started showing width
>> x0.
>> >
>> > By adding debug prints, I've found out there were devices up the chain that
>> > Showed 0 when their PCI_EXP_LNKSTA was read by said function.
>> > However, when I tried looking via lspci the output claimed the width was
>> x4.
>>
>> I don't see a 'pcie_get_minimum_link()' function in my current tree
>> (git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git "next"
>> branch).  Maybe seeing your patch (with the debug prints) would give
>> me a hook for somewhere to start looking.
>
> You've acked the patch and it was applied in net-next; Obviously it has yet
> to migrate to your tree.

Oh, yeah, that's right.  I knew it sounded familiar, but I didn't
remember where it went.

Looking at its implementation, one obvious difference is that
pcie_get_minimum_link() traverses up the hierarchy and keeps track of
the minimum values it finds.  lspci, on the other hand, just reads
PCI_EXP_LNKSTA from a single device and decodes it.

You said lspci reports x4 for every device from the Root Port all the
way down to your NIC, so I would think the minimum from
pcie_get_minimum_link() would be x4.  But apparently it's not.  Maybe
there's a bug in it.  Can you post the complete "lspci -vv" output
along with your debug patch and output?

Bjorn
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