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SubjectRe: [patch] SGIIOC4 limit request size
On 01 Feb 2006 03:59:16 -0500, Jes Sorensen <jes@sgi.com> wrote:
> Hi,

Hi,

> This one takes care of a problem with the SGI IOC4 driver where it
> hits DMA problems if the request grows too large.

Does this happen only for CONFIG_IA64_PAGE_SIZE_4KB=y
or CONFIG_IA64_PAGE_SIZE_8KB=y?

from sgiioc4.c:

/* Each Physical Region Descriptor Entry size is 16 bytes (2 * 64 bits) */
/* IOC4 has only 1 IDE channel */
#define IOC4_PRD_BYTES 16
#define IOC4_PRD_ENTRIES (PAGE_SIZE /(4*IOC4_PRD_BYTES))
As limiting request size to 127 sectors punishes performance
wouldn't it be better to define IOC4_PRD_ENTRIES to 256
if this is possible (would need 4 pages for PAGE_SIZE=4096
and 2 for PAGE_SIZE=8192)?

Cheers.
Bartlomiej

> Cheers,
> Jes
>
> Avoid requests larger than the number of SG table entries, to avoid
> DMA timeouts.
>
> Signed-off-by: Jes Sorensen <jes@sgi.com>
>
> ----
>
> drivers/ide/pci/sgiioc4.c | 8 +++++++-
> 1 files changed, 7 insertions(+), 1 deletion(-)
>
> Index: linux-2.6/drivers/ide/pci/sgiioc4.c
> ===================================================================
> --- linux-2.6.orig/drivers/ide/pci/sgiioc4.c
> +++ linux-2.6/drivers/ide/pci/sgiioc4.c
> @@ -1,5 +1,5 @@
> /*
> - * Copyright (c) 2003 Silicon Graphics, Inc. All Rights Reserved.
> + * Copyright (C) 2003, 2006 Silicon Graphics, Inc. All Rights Reserved.
> *
> * This program is free software; you can redistribute it and/or modify it
> * under the terms of version 2 of the GNU General Public License
> @@ -613,6 +613,12 @@
> hwif->ide_dma_lostirq = &sgiioc4_ide_dma_lostirq;
> hwif->ide_dma_timeout = &__ide_dma_timeout;
> hwif->INB = &sgiioc4_INB;
> +
> + /*
> + * Limit the request size to avoid DMA timeouts when
> + * requesting more entries than goes in the sg table.
> + */
> + hwif->rqsize = 127;
> }
>
> static int __devinit
-
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