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

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Date:	Sun, 04 May 2014 16:48:14 +0300
From:	Ronen Hod <rhod@...hat.com>
To:	Marcel Apfelbaum <marcel.a@...hat.com>, linux-pci@...r.kernel.org
CC:	linux-kernel@...r.kernel.org, bhelgaas@...gle.com, matthew@....cx,
	mst@...hat.com
Subject: Re: [PATCH] PCI/shpchp: fix a bus speed issue on hotplug

On 05/01/2014 05:35 PM, Marcel Apfelbaum 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).

Since the speed is irrelevant when running in a VM, I suggest that
you either ignore it altogether, or "normalize" the speed of all the
devices/bridges/buses in QEMU in order to avoid any conflicts
in the first place.

Thanks, Ronen.

>
> 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".
>
> 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))

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