Re: [PATCH] ieee1394: sbp2: lower block queue alignment requirement

[Mike Christie <michaelc@cs.wisc.edu>]

Kristian Høgsberg wrote:
> On 1/14/07, Stefan Richter <stefanr@s5r6.in-berlin.de> wrote:
>> On 14 Jan, James Bottomley wrote:
>> > The block layer currently provides sector (512) byte alignment
>> > guarantees.  However, there has been talk in SCSI of reducing that to
>> > word (4) since that's what most intelligent PCI controllers can cope
>> > with.  If you have any alignment constraints, they should be expressed
>> > in the slave configure.
>>
>> OK, thanks. I will keep the explicit setting of the mask then.
>> I actually think that everything should work just fine with 4 bytes
>> alignment, but the SBP-2 spec mentiones 8 bytes alignment for the S/G
>> tables.  So maybe device firmwares will expect it that way even though
>> IEEE 1394 doesn't impose such a restriction even on transfers with a
>> payload of a multiple of 8 bytes.
> 
> Do you have a reference to this 8 byte alignment requirement?  I
> couldn't find it browsing through the standard.  Also, since the SBP-2
> driver has to  convert the scatterlist to an SBP-2 page table, it can
> just allocate the page table on a 8-byte boundary if that is required.
> The entries in the scatter table have no alignment restrictions from
> the SBP-2 side.
> 
> By the way, is there a way to ask the SCSI stack to limit the size of
> the entries in the scatterlist to 64k?  This would greatly simplify
> the conversion to SBP-2 page tables, since this is the maximum size
> these can hold.
> 

I think 64k is the limit already, but I think you can call
blk_queue_max_segment_size in your scsi_host_template->slave_configure
or slave_alloc to set the size to whatever you like.
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