linux-kernel - Re: [PATCH 0/3] fix GART to respect device's dma

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Message-ID: <20080922203518.GZ25711@one.firstfloor.org>
Date:	Mon, 22 Sep 2008 22:35:18 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	andi@...stfloor.org, mingo@...e.hu, joerg.roedel@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] fix GART to respect device's dma_mask about virtual mappings

On Tue, Sep 23, 2008 at 04:12:33AM +0900, FUJITA Tomonori wrote:
> Sure, pci-nommu's map_sg/map_single doesn't handle it. But we handle
> this issue somewhere else (like b44 keeps own DMA buffer)?

Yes, b44 handles it on its own. It has to for 32bit which always
has a nop map_sg/single. Also some other subsystems like the block layer
do it implicitely.

> 1. not all map_sg/map_single (e.g. pci-nommu) can't handle it.

and especially i386

> 2. we already have workarounds for it somewhere else so
> map_sg/map_single don't need to handle it.
> 3. I changed GART map_sg/map_signle to handle it. I thought if it
> can handle it, for example, b44 doesn't go the workaround path. It
> would be a good thing.
> 4. But GART cannot remap to addresses < 4GB reliably, so my above
> argument doesn't always work.
> 5. Then my patch doesn't break anything but it's almost meaningless.

Correct.

-Andi
-- 
ak@...ux.intel.com
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