linux-kernel - Re: [PATCH] firewire: Enable physical DMA above 4GB

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Message-ID: <1364556661.3559.63.camel@thor.lan>
Date:	Fri, 29 Mar 2013 07:31:01 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	Stefan Richter <stefanr@...6.in-berlin.de>,
	linux1394-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firewire: Enable physical DMA above 4GB

On Fri, 2013-03-29 at 12:19 +0100, Clemens Ladisch wrote:
> Peter Hurley wrote:
> > On Fri, 2013-03-29 at 11:44 +0100, Stefan Richter wrote:
> >>> On Mar 26 Peter Hurley wrote:
> >>>> The FW643e-2 is natively PCIe (not behind a bridge) and supports phys
> >>>> DMA past 4GB (the datasheet says all 48 bits but I can only test it out
> >>>> to 10GB).
> >>>>
> >>>> I thought the FW643e was as well? You'll have to test that out :)
> >>
> >> Does lspci or something similar show which PCI devices are capable of 64 bit
> >> wide addressing?
> >
> > Not definitively.
> >
> > Usually (but not always), if the host registers are 64-bit addressable,
> > then the device supports DAC.
> 
> DACs are a feature of conventional PCI.
> 
> All PCI Express devices are 64-bit addressable.  In the lspci output, PCIe
> devices have the "Express" capability.

The "device" could be sitting behind a PCIe-PCI bridge that _only_
supports the host window for 64-bit. All other 64-bit decodes could
return garbage.

> However, whether a device can *generate* 64-bit DMA requests is completely
> device-specific.


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