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

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Date:	Thu, 01 May 2014 21:13:45 +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 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.

I didn't check the other hotplug drivers, but I do plan
to look into PCIe driver as part of QEMU's PCIe hotplug feature.

Thanks,
Marcel

> 
> > Fixed that by checking the speed against the subordinate bus.
> >
> > Signed-off-by: Marcel Apfelbaum <marcel.a@...hat.com>
> > Acked-by: Michael S. Tsirkin <mst@...hat.com>
> > ---
> >  drivers/pci/hotplug/shpchp_ctrl.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/hotplug/shpchp_ctrl.c b/drivers/pci/hotplug/shpchp_ctrl.c
> > index 5849927..6efc2ec 100644
> > --- a/drivers/pci/hotplug/shpchp_ctrl.c
> > +++ b/drivers/pci/hotplug/shpchp_ctrl.c
> > @@ -282,8 +282,8 @@ static int board_added(struct slot *p_slot)
> >                 return WRONG_BUS_FREQUENCY;
> >         }
> >
> > -       bsp = ctrl->pci_dev->bus->cur_bus_speed;
> > -       msp = ctrl->pci_dev->bus->max_bus_speed;
> > +       bsp = ctrl->pci_dev->subordinate->cur_bus_speed;
> > +       msp = ctrl->pci_dev->subordinate->max_bus_speed;
> >
> >         /* Check if there are other slots or devices on the same bus */
> >         if (!list_empty(&ctrl->pci_dev->subordinate->devices))
> > --
> > 1.8.3.1
> >



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