linux-kernel - Re: [PATCH bugfix 3.9] PCI: Don't try to disable Bus Master on disconnected PCI devices

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Date:	Mon, 01 Apr 2013 12:00:01 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	linux-kernel@...r.kernel.org
CC:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	kexec@...ts.infradead.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jeff Garzik <jgarzik@...ox.com>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH bugfix 3.9] PCI: Don't try to disable Bus Master on disconnected
 PCI devices

BUMP. This is degradation from 3.8, so this patch must be in 3.9.

I still don't like this forced clearing bus-master bit. But this hack
definitely fixes problems in kexec, so there is reason to keep it here.

Konstantin Khlebnikov wrote:
> This is fix for commit 7897e6022761ace7377f0f784fca059da55f5d71 from v3.9-rc1
> ("PCI: Disable Bus Master unconditionally in pci_device_shutdown()")
> in turn that was fix for b566a22c23327f18ce941ffad0ca907e50a53d41 from v3.5-rc1
> ("PCI: disable Bus Master on PCI device shutdown")
>
> Unfortunately fixing one bug uncovers another:
> ->shutdown() callback might switch device to deep sleep state.
> PCI config space no longer available after that.
>
> Link: https://lkml.org/lkml/2013/3/12/529
> Signed-off-by: Konstantin Khlebnikov<khlebnikov@...nvz.org>
> Reported-and-Tested-by: Vivek Goyal<vgoyal@...hat.com>
> Cc: Bjorn Helgaas<bhelgaas@...gle.com>
> Cc: Rafael J. Wysocki<rafael.j.wysocki@...el.com>
> ---
>   drivers/pci/pci-driver.c |    5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 1fa1e48..79277fb 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -390,9 +390,10 @@ static void pci_device_shutdown(struct device *dev)
>
>   	/*
>   	 * Turn off Bus Master bit on the device to tell it to not
> -	 * continue to do DMA
> +	 * continue to do DMA. Don't touch devices in D3cold or unknown states.
>   	 */
> -	pci_clear_master(pci_dev);
> +	if (pci_dev->current_state <= PCI_D3hot)
> +		pci_clear_master(pci_dev);
>   }
>
>   #ifdef CONFIG_PM
>

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