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To: Arnd Bergmann <ibm.com@arndb.de>
cc: "J.E.J. Bottomley" <James.Bottomley@SteelEye.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>,
       Linux Scsi <linux-scsi@vger.kernel.org>,
       Mike Anderson <andmike@us.ibm.com>
Subject: Re: [RFC][PATCH] move dma_mask into struct device 
In-Reply-To: Message from Arnd Bergmann <arndb@de.ibm.com> 
   of "Sat, 16 Nov 2002 18:23:48 +0100." <200211161823.48018.arndb@de.ibm.com> 
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From: "J.E.J. Bottomley" <James.Bottomley@steeleye.com>
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arndb@de.ibm.com said:
> That does not sound like the right way to me. If you need to have the
> dma_mask for the Scsi_Host, you should store it in Scsi_Host itself. A
> struct device must never know about obscure architecture specific
> stuff like dma.

The SCSI host itself has no need of a DMA mask.  What we need the mask for is 
to set up the bounce limits for the block queue, we don't actually ever use it 
again.  Unfortunately, dma_mask isn't architecture specific, its a universal 
property of the block queues used to determine when to bounce memory regions.

The dma_mask is a property of the connection of the Scsi_Host to the machine 
bus, not of the Scsi_Host itself, so it does properly belong in the generic 
device which is used to reflect machine bus attachments.

Think of it this way: we have two struct device's per SCSI host: one for the 
actual HBA card or bus attachment, which contains all of the bus specific 
pieces, and one for the host itself reflecting the fact that it is a bridge 
from the machine bus to the scsi bus.

James



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