Re: [PATCH 1/3] iscsi iser: remove DMA restrictions

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Tue, 2008-02-12 at 15:54 -0500, Pete Wyckoff wrote:
> iscsi_iser does not have any hardware DMA restrictions.  Add a
> slave_configure function to remove any DMA alignment restriction,
> allowing the use of direct IO from arbitrary offsets within a page.
> Also disable page bouncing; iser has no restrictions on which pages it
> can address.
> 
> Signed-off-by: Pete Wyckoff <pw@osc.edu>
> ---
>  drivers/infiniband/ulp/iser/iscsi_iser.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/infiniband/ulp/iser/iscsi_iser.c b/drivers/infiniband/ulp/iser/iscsi_iser.c
> index be1b9fb..1b272a6 100644
> --- a/drivers/infiniband/ulp/iser/iscsi_iser.c
> +++ b/drivers/infiniband/ulp/iser/iscsi_iser.c
> @@ -543,6 +543,13 @@ iscsi_iser_ep_disconnect(__u64 ep_handle)
>  	iser_conn_terminate(ib_conn);
>  }
>  
> +static int iscsi_iser_slave_configure(struct scsi_device *sdev)
> +{
> +	blk_queue_bounce_limit(sdev->request_queue, BLK_BOUNCE_ANY);

You really don't want to do this.  That signals to the block layer that
we have an iommu, although it's practically the same thing as a 64 bit
DMA mask ... but I'd just leave it to the DMA mask to set this up
correctly.  Anything else is asking for a subtle bug to turn up years
from now when something causes the mask and the limit to be mismatched.

James