linux-kernel - Re: [PATCH] PCI/shpchp: fix a bus speed issue on hotplug

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Date:	Thu, 01 May 2014 23:36:37 +0300
From:	Marcel Apfelbaum <marcel.a@...hat.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Matthew Wilcox <matthew@....cx>,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH] PCI/shpchp: fix a bus speed issue on hotplug

On Thu, 2014-05-01 at 14:00 -0600, Bjorn Helgaas wrote:
> On Thu, May 1, 2014 at 12:57 PM, Marcel Apfelbaum
> <marcel.apfelbaum@...il.com> wrote:
> > On Thu, 2014-05-01 at 21:13 +0300, Marcel Apfelbaum wrote:
> >> On Thu, 2014-05-01 at 12:02 -0600, Bjorn Helgaas wrote:
> >> > On Thu, May 1, 2014 at 8:35 AM, Marcel Apfelbaum <marcel.a@...hat.com> wrote:
> >> > > When a board is added, the shpchp driver checks if there
> >> > > is a mismatch between the bridge's adapter and the bus speed.
> >> > > If there is, it sets the subordinate speed (if there is no device on it).
> >> > >
> >> > > However, it takes the reference of the board speed from the primary bus
> >> > > and not from the subordinate. If the primary bus is PCI and not PCIX/PCIe,
> >> > > its speed is not updated and remains 0xff. As a result hotplug fails
> >> > > with error: "Speed of bus ff and adapter 0 mismatch".
> >> >
> >> > It'd be cool to have a bugzilla for this with lspci and dmesg output.
> >> > I'll also have to check the other hotplug drivers for similar issues,
> >> > unless you've already done that.
> >> I'll open a BZ with the details, sure.
> > Done: https://bugzilla.kernel.org/show_bug.cgi?id=75251
> > If you need further details, please let me know.
> 
> Thanks.  Would you mind attaching the "lspci -vv" output?  That should
> show more details, including the information used to compute the bus
> speed.
Sure, done.

> 
> Also, you checked the "regression" box.  Can you confirm that and
> identify a known-working kernel?  If we know which kernels are broken,
> we can potentially mark the fix to be backported to them.
I checked the regression box based on Michael's comment that in early 2009 it did work.
He pointed out a commit he thinks that caused this regression.

I think it can be backported to all the relevant stable versions since
the commit that introduced the code mentioned in the patch.

Thanks,
Marcel

> 
> Bjorn



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