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Date:	Tue, 04 Dec 2007 19:09:09 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	ide <linux-ide@...r.kernel.org>, Tejun Heo <htejun@...il.com>
Subject: Re: [PATCH] sata_nv: fix ADMA ATAPI issues with memory over 4GB (v3)

Jeff Garzik wrote:
> Robert Hancock wrote:
>> This fixes some problems with ATAPI devices on nForce4 controllers in 
>> ADMA mode
>> on systems with memory located above 4GB. We need to delay setting the 
>> 64-bit
>> DMA mask until the PRD table and padding buffer are allocated so that 
>> they don't
>> get allocated above 4GB and break legacy mode (which is needed for ATAPI
>> devices).
>>
>> Signed-off-by: Robert Hancock <hancockr@...w.ca>
> 
> This is a bit nasty :/
> 
> I would consider setting the consistent DMA mask to 32-bit, and setting 
> the overall mask to 64-bit.
> 
> Seems like that would solve the problem?

The issue with that is that it would also constrain the ADMA CPB/PRD 
table allocation to 32-bit, which I'd rather avoid having to do. There 
are dual-socket Opteron boxes like HP xw9300 that use this controller, 
and limiting the allocation to 32-bit could force a non-optimal node 
allocation for the table memory.

These type of devices really want a version of dma_alloc_coherent that 
allows overriding the DMA mask for specific allocations to make this 
cleaner. I'm sure this isn't the only device that has different DMA mask 
requirements for different consistent memory allocations..

This patch does has the advantage of being confirmed to fix the 
reporter's problem (https://bugzilla.redhat.com/show_bug.cgi?id=351451) 
which there's something to be said for this late in the .24-rc series..

> 
> Also, does this need to be rebased on top of what I just pushed upstream?

It don't think so.. this change is independent from the "sata_nv: don't 
use legacy DMA in ADMA mode (v3)" patch you just merged.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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