linux-kernel - Re: [PATCH 0/3] x86: restore old GART alloc

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Message-ID: <20080924125808.GU24392@amd.com>
Date:	Wed, 24 Sep 2008 14:58:08 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	mingo@...e.hu, linux-kernel@...r.kernel.org, andi@...stfloor.org
Subject: Re: [PATCH 0/3] x86: restore old GART alloc_coherent

On Wed, Sep 24, 2008 at 08:48:34PM +0900, FUJITA Tomonori wrote:
> This pachset is against tip/iommu.
> 
> What this patchset does is restoring old GART alloc_coherent behavior
> (before the alloc_coherent rewrite):
> 
> http://lkml.org/lkml/2008/8/12/200
> 
> Currently, GART alloc_coherent tries to allocate pages with GFP_DMA32
> for a device having dma_masks > 24bit < 32bits. If GART gets an
> address that a device can't access to, GART tries to map the address
> to a virtual I/O address that the device can access to.
> 
> But Andi pointed out, "The GART is somewhere in the 4GB range so you
> cannot use it to map anything < 4GB. Also GART is pretty small."
> 
> http://lkml.org/lkml/2008/9/12/43
> 
> So it's possible that GART doesn't have virtual I/O address space that
> a device can access to. The current behavior might not work for a
> device having dma_masks > 24bit < 32bits. This patchset restores old
> GART alloc_coherent behavior, which doesn't use GART hardware (if an
> user doesn't enable force_iommu option).

Acked-by: Joerg Roedel <joerg.roedel@....com>

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