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From: Andi Kleen <andi@firstfloor.org>
To: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: andi@firstfloor.org, mingo@elte.hu, joerg.roedel@amd.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] fix GART to respect device's dma_mask about virtual mappings
Date: Tue, 16 Sep 2008 19:58:24 +0200	[thread overview]
Message-ID: <20080916175824.GF25711@one.firstfloor.org> (raw)
In-Reply-To: <20080917021319O.fujita.tomonori@lab.ntt.co.jp>

> > Those always are handled elsewhere in the block layer (using the bounce_pfn
> > mechanism)
> 
> I don't think that the bounce guarantees that dma_alloc_coherent()
> returns an address that a device can access to.

dma_alloc_coherent() is not used for block IO data. And dma_alloc_coherent()
does handle masks > 24bit < 32bits just fine.


> I'm not familiar with what the networking does, for example, seems
> that b44 sets dev->dma_mask to DMA_30BIT_MASK and b44_start_xmit()
> does:
> 

b44 (and related designs like the bcm wireless chipset) 
has its own bouncing scheme. IT doesn't need any hacks in map_sg
 
> IOMMUs can try to return an address that the NIC can access to.

It's not worth to handle this strange case. The drivers do anyways.
These are very cheap devices which are only rarely used in systems
with >2GB and for those cases the existing bouncing setup works fine.

-Andi

-- 
ak@linux.intel.com

  reply	other threads:[~2008-09-16 17:54 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-09-12 10:42 FUJITA Tomonori
2008-09-12 10:42 ` [PATCH 1/3] add iommu_device_max_index IOMMU helper function FUJITA Tomonori
2008-09-12 10:42   ` [PATCH 2/3] add dma_get_mask " FUJITA Tomonori
2008-09-12 10:42     ` [PATCH 3/3] x86: make GART to respect device's dma_mask about virtual mappings FUJITA Tomonori
2008-09-12 14:52       ` Joerg Roedel
2008-09-12 15:11         ` FUJITA Tomonori
2008-09-14 14:45 ` [PATCH 0/3] fix " Ingo Molnar
2008-09-16  0:54 ` Andi Kleen
2008-09-16 13:20   ` FUJITA Tomonori
2008-09-16 13:43     ` Andi Kleen
2008-09-16 17:13       ` FUJITA Tomonori
2008-09-16 17:58         ` Andi Kleen [this message]
2008-09-16 23:53           ` FUJITA Tomonori
2008-09-17  0:24             ` Andi Kleen
2008-09-17 19:20               ` FUJITA Tomonori
2008-09-18 18:20                 ` Andi Kleen
2008-09-18 22:15                   ` FUJITA Tomonori
2008-09-19  0:44                     ` Andi Kleen
2008-09-22 19:12                       ` FUJITA Tomonori
2008-09-22 20:35                         ` Andi Kleen
2008-09-23  4:02                           ` FUJITA Tomonori
2008-09-17 10:43             ` Ingo Molnar
2008-09-18 18:25               ` Andi Kleen
2008-09-16 15:52     ` Joerg Roedel
2008-09-16 16:20       ` Andi Kleen

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