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

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Message-ID: <515578D0.9090701@ladisch.de>
Date:	Fri, 29 Mar 2013 12:19:44 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	Peter Hurley <peter@...leysoftware.com>
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

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.

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


Regards,
Clemens
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