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

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Date:	Wed, 3 Apr 2013 10:15:09 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	kexec@...ts.infradead.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jeff Garzik <jgarzik@...ox.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH bugfix 3.9] PCI: Don't try to disable Bus Master on
 disconnected PCI devices

[+cc linux-pci]

On Mon, Apr 1, 2013 at 2:00 AM, Konstantin Khlebnikov
<khlebnikov@...nvz.org> wrote:
> 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.

Applied to for-linus for v3.9, thanks!

> 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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