netdev - Re: r8169 64-bit DMA support

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Message-ID: <20090922115356.GB13710@electric-eye.fr.zoreil.com>
Date:	Tue, 22 Sep 2009 13:53:56 +0200
From:	Francois Romieu <romieu@...zoreil.com>
To:	Robert Hancock <hancockrwd@...il.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: r8169 64-bit DMA support

Robert Hancock <hancockrwd@...il.com> :
[...]
> It's not clear (from the mails I've read) exactly what was going on in  
> the case that caused this to be added.

Some AMD + r8169 systems simply did not work.

> Normally these days the PCI subsystem is supposed to detect that DAC
> isn't usable on a machine and refuse setting 64-bit DMA masks, it's
> not the driver's responsibility to handle this.
> I'm guessing that when this change was made that detection didn't exist
> though.

Not exactly. It was required for DAC to be explicitely enabled through
the CPlusCmd register.

> Thoughts on whether this default can be changed now ?

The 8168 does not seem to need the CPlusCmd stuff. I'll check it but it
should be possible to enable high DMA without condition for it.

-- 
Ueimor
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