Re: [PATCH 1/5] add dma_max_segment_size option to scsi_host_template

[Jeff Garzik <jeff@garzik.org>]

FUJITA Tomonori wrote:
> This patch moves blk_queue_max_segment_size to scsi_alloc_queue from
> llds. It enables scsi_add_host to tells iommu lld's
> dma_max_segment_size. If a low-level driver doesn't specify
> dma_max_segment_size, scsi-ml uses 65536 (MAX_SEGMENT_SIZE). So there
> are not any functional changes.
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
> ---
>  drivers/scsi/hosts.c     |    5 +++++
>  drivers/scsi/scsi_lib.c  |    1 +
>  include/scsi/scsi_host.h |    6 ++++++
>  3 files changed, 12 insertions(+), 0 deletions(-)

hmmmmm...  All the patches look technically correct, but IMO this really 
should behave more the the dma_mask interface:  platform sets a sane 
dma_mask (usually 0xffffffff), and LLDD calls dma_set_mask() or 
pci_set_dma_mask().

Thus, IMO an LLDD should call dma_set_max_seg(), and then SCSI midlayer 
can obtain that value from struct device.

Just like dma_mask, I think we can avoid a scsi_host_template addition.

I echo Jens sentiment, though, in closing:  thanks for doing this work, 
it's been needed for quite a while.

	Jeff