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From: FUJITA Tomonori <>
Subject: Re: more iommu sg merging fallout
Date: Thu, 07 Feb 2008 08:12:36 +0900	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, 05 Feb 2008 20:41:38 -0800 (PST)
David Miller <> wrote:

> The sparc64 change:
>     commit fde6a3c82d67f592eb587be4d12222b0ae6d4321
>     Author: FUJITA Tomonori <>
>     Date:   Mon Feb 4 22:28:02 2008 -0800
>     iommu sg merging: sparc64: make iommu respect the segment size limits
>     This patch makes iommu respect segment size limits when merging sg
>     lists.
>     Signed-off-by: FUJITA Tomonori <>
>     Cc: Jeff Garzik <>
>     Cc: James Bottomley <>
>     Acked-by: Jens Axboe <>
>     Cc: "David S. Miller" <>
>     Signed-off-by: Andrew Morton <>
>     Signed-off-by: Linus Torvalds <>
> has significant errors and is going to eat people's disks, as it just
> nearly did to mine.

Really sorry about it.

> Typically what you'll see are NULL pointer derefernces in
> dma_4v_map_sg() and dma_4u_map_sg() and then the kernel usually craps
> on your superblock very shortly thereafter.
> The changeset above modified only prepare_sg() but that is only the
> first pass of the SG mapping algorithm of the sparc64 IOMMU layer.
> The second pass that fills in the entries depends upon how the first
> pass does things.  So if you change the first pass decision making you
> have to update the second pass's as well.
> That second pass is implemented in fill_sg() (there is a version in
> both arch/sparc64/kernel/iommu.c and arch/sparc64/kernel/pci_sun4v.c),
> which probably needs new logic as was added to prepare_sg() to handle
> dma_get_max_seg_size().

PARISC, Alpha, and IA64 IOMMUs use the two-pass algorithm like SPARC
but their first pass decides how to merge sg entires (and stores that
information in the sg entries), then the second pass simpliy follows
it (Hopefully I understand these IOMMUs correctly, or else I break
them too).

I'll try this work again for 2.6.26. The SPARC IOMMUs are the most
complicated and seems that few people tests the -mm SPARC code. So I
guess that I need to find a SPARC box...


  reply	other threads:[~2008-02-06 23:17 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-06  4:41 David Miller
2008-02-06 23:12 ` FUJITA Tomonori [this message]
2008-02-06 23:18   ` David Miller
2008-02-06 23:53     ` FUJITA Tomonori
2008-02-07  0:01       ` David Miller
2008-02-07  1:38         ` FUJITA Tomonori
2008-02-12  5:40           ` David Miller
2008-02-16  6:03             ` FUJITA Tomonori
2008-02-18  7:41               ` David Miller
2008-02-19 10:57                 ` FUJITA Tomonori
2008-02-21  6:56                   ` David Miller

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