linux-kernel - Re: [PATCH] Disable Bus Master on PCI device shutdown

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Date:	Thu, 07 Jun 2012 10:08:31 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Matthew Garrett <mjg@...hat.com>
Cc:	Khalid Aziz <khalid.aziz@...com>, linux-kernel@...r.kernel.org,
	bhelgaas@...gle.com, linux-pci@...r.kernel.org
Subject: Re: [PATCH] Disable Bus Master on PCI device shutdown

Matthew Garrett <mjg@...hat.com> writes:
>
> This protects against the case where a piece of hardware is continuing 
> to DMA even after the driver shutdown method has been called? I'm not 
> convinced this is safe. Some Broadcom parts will crash if busmastering 
> is disabled while they're still performing DMA, and they'll then hang 
> the bus if reenabled. There's also the risk that the hardware will start 
> DMAing again if it's reenabled after being shut down. It seems like 
> you're covering over the case where the driver didn't correctly quiesce 
> the hardware, but you risk triggering other bugs instead.

One alternative I've been pondering some time is to use AER link reset
instead. But this is mainly on servers, a lot of clients don't have it.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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