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

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Message-ID: <20080924140644.569cdd1d@lxorguk.ukuu.org.uk>
Date:	Wed, 24 Sep 2008 14:06:44 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org, andi@...stfloor.org,
	joerg.roedel@....com, fujita.tomonori@....ntt.co.jp
Subject: Re: [PATCH 3/3] x86: restore old GART alloc_coherent behavior

On Wed, 24 Sep 2008 20:48:37 +0900
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:

> 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 try 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
> 
> That is, it's possible that GART doesn't have virtual I/O address
> space that a device can access to. The above behavior doesn't work for
> a device having dma_masks > 24bit < 32bits.
> 
> This patch restores old GART alloc_coherent behavior (before the
> alloc_coherent rewrite).
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>

Acked-by: Alan Cox <alan@...hat.com>

This is indeed a specific problem found with things like older AACRAID
where control blocks must be below 31bits and the GART is above 0x80000000

Alan
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