linux-kernel - Re: [RFC PATCH] Let device drivers disable msi on shutdown

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Date:	Thu, 10 Jul 2014 13:53:36 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Keith Busch <keith.busch@...el.com>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	Nagalakshmi Nandigama <Nagalakshmi.Nandigama@....com>,
	Sreekanth Reddy <Sreekanth.Reddy@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] Let device drivers disable msi on shutdown

On Thu, Jul 10, 2014 at 12:53 PM, Keith Busch <keith.busch@...el.com> wrote:
> On Thu, 10 Jul 2014, Bjorn Helgaas wrote:
>>
>> [+cc LKML, Greg KH for driver core async shutdown question]
>> On Tue, Jun 24, 2014 at 10:48:57AM -0600, Keith Busch wrote:
>>>
>>> To provide context why I want to do this asynchronously, NVM-Express has
>>> one PCI device per controller, of which there could be dozens in a
>>> system,
>>> and each one may take many seconds (I've heard over ten in some cases)
>>> to safely shutdown.
>>
>>
>> I don't see anything in device_shutdown() that would wait for this
>> sort of asynchronous shutdown to complete.  So how do we know it's
>> finished before we turn off the power, reset, kexec, etc.?
>>
>> If we need to do asynchronous shutdown, it seems like we need some
>> sort of driver core infrastructure to manage that.
>
>
> Yes, good point! To address that, I did submit this patch:
>
> http://lists.infradead.org/pipermail/linux-nvme/2014-May/000827.html
>
> I need to fix the EXPORT_SYMBOL_GPL usage for a v2, but before that, I
> wan't to know the reason the driver can't use MSIx in an async shutdown
> shutdown, and came to the patch mentioned above.
>
> I'd originally had the async shutdown use legacy interrupts, but I
> know some NVMe devices do not support legacy, so can't use my original
> proposal. If I can't rely on MSI/MSI-x being enabled in an async shutdown,
> then I have to add polling, which I suppose we can live with.

OK, I wasn't aware of your async shutdown patch.  Given that, I would
think we'd want to somehow delay the rest of pci_device_shutdown()
until after the driver's async shutdown completes.  We don't want to
do either the MSI shutdown or the pci_clear_master() until after it
completes, do we?  And if we delay that, there would be no need to
move the MSI shutdown from the core to the driver.

Bjorn
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