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

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Message-ID: <20140515184146.GA14506@google.com>
Date:	Thu, 15 May 2014 12:41:46 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Marcel Apfelbaum <marcel.a@...hat.com>
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	matthew@....cx, mst@...hat.com
Subject: Re: [PATCH] PCI/shpchp: fix a bus speed issue on hotplug

On Thu, May 01, 2014 at 05:35:48PM +0300, 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).
> 
> 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>

I think cpqphp has similar issues.  But I can't test it and I don't know if
anybody even uses it any more, so I'm just going to leave it alone.

I reworked the changelog because I got confused about the bridge, adapter,
board, and what was what.  Let me know if the one below is inaccurate.

I'll include this for v3.15 since it's a regression fix.

Thanks,
  Bjorn

commit be219b7f518a36f62d67f057e9d31ebe9674814f
Author: Marcel Apfelbaum <marcel.a@...hat.com>
Date:   Thu May 1 17:35:48 2014 +0300

    PCI: shpchp: Check bridge's secondary (not primary) bus speed
    
    When a new device is added below a hotplug bridge, the bridge's secondary
    bus speed and the device's bus speed must match.  The shpchp driver
    previously checked the bridge's *primary* bus speed, not the secondary bus
    speed.
    
    This caused hot-add errors like:
    
      shpchp 0000:00:03.0: Speed of bus ff and adapter 0 mismatch
    
    Check the secondary bus speed instead.
    
    [bhelgaas: changelog]
    Link: https://bugzilla.kernel.org/show_bug.cgi?id=75251
    Fixes: 3749c51ac6c1 ("PCI: Make current and maximum bus speeds part of the PCI core")
    Signed-off-by: Marcel Apfelbaum <marcel.a@...hat.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
    Acked-by: Michael S. Tsirkin <mst@...hat.com>
    CC: stable@...r.kernel.org	# v2.6.34+

diff --git a/drivers/pci/hotplug/shpchp_ctrl.c b/drivers/pci/hotplug/shpchp_ctrl.c
index 58499277903a..6efc2ec5e4db 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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