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

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Message-Id: <1222256917-14321-1-git-send-email-fujita.tomonori@lab.ntt.co.jp>
Date:	Wed, 24 Sep 2008 20:48:34 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	mingo@...e.hu
Cc:	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	joerg.roedel@....com, fujita.tomonori@....ntt.co.jp
Subject: [PATCH 0/3] x86: restore old GART alloc_coherent

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).

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