linux-kernel - Re: [PATCH 2.6.34] r8169: enable 64-bit DMA by default for PCI Express devices (v2)

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Message-Id: <20100219.171025.09226171.davem@davemloft.net>
Date:	Fri, 19 Feb 2010 17:10:25 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	hancockrwd@...il.com
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	romieu@...zoreil.com
Subject: Re: [PATCH 2.6.34] r8169: enable 64-bit DMA by default for PCI
 Express devices (v2)

From: Robert Hancock <hancockrwd@...il.com>
Date: Fri, 19 Feb 2010 19:00:46 -0600

> Currently use of 64-bit DMA is disabled in r8169 unless the user passes the
> use_dac module option. This is reasonable for conventional PCI devices where
> broken chipsets may not handle dual-address-cycle transfers properly for
> 32-bit slots and so this may not be safe. However, PCI Express should not have
> this problem and not using 64-bit DMA results in DMA transfers needlessly using
> the IOMMU or SWIOTLB. Set the use_dac module parameter to a new default value of
> -1 which results in 64-bit DMA being enabled by default for PCI Express devices
> only.
> 
> Signed-off-by: Robert Hancock <hancockrwd@...il.com>

Applied, thanks Robert.
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