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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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