linux-kernel - Re: linux-next: build failure after merge of the final tree (net-next tree related)

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Message-Id: <20120920.185315.576326460331670020.davem@davemloft.net>
Date:	Thu, 20 Sep 2012 18:53:15 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	benh@...nel.crashing.org
Cc:	sfr@...b.auug.org.au, paulus@...ba.org,
	linuxppc-dev@...ts.ozlabs.org, mika.westerberg@...ux.intel.com,
	netdev@...r.kernel.org, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: linux-next: build failure after merge of the final tree
 (net-next tree related)

From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Date: Fri, 21 Sep 2012 08:22:44 +1000

> Hrm, that's ancient gunk, I'll have to dig. We potentially can support
> ISA devices DMA'ing from an ISA bridge... but via the iommu, which means
> isa_virt_to_bus is a non-starter.
> 
> But then, do we really care ? IE. Is there single device that actually
> requires ISA_DMA_API and that is expected to work on any currently
> supported powerpc hw ? :-)
> 
> We don't even support PReP anymore, so that leaves us with what ?

ISA_DMA_API implies a fixed window of addresses which are <= 32-bits
on the bus, which is a hardware requirement of these devices.

isa_virt_to_bus() goes to that physical address, and the expection is
that you use GFP_DMA and thus the physical addresses fit inside of
an unsigned int.

isa_virt_to_bus() basically amounts to a virt-->phys plus a cast.

> Anybody has an objection to turning ISA_DMA_API off ?

Then you can remove all of the DMA api stuff in powerpc's asm/dma.h
but some of it looks like it might be in use.
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