Re: libata+SGIO: is .dma_boundary respected?

[Mark Lord <liml@rtr.ca>]

Jeff Garzik wrote:
> Mark Lord wrote:
>> Jens / Jeff,
>>
>> Each libata driver registers a .dma_boundary field with SCSI.
>> This field is used to prevent merging of bio segments across
>> a hardware limitation boundary, usually 0xffff.
>>
>> This looks like it works for regular block I/O,
>> but I'm not so sure about SGIO originated requests.
>>
>> Any thoughts, or code you can point me to?
> 
> Everything goes through the block layer, including SG_IO, so everyone 
> agrees on the boundaries that must be respected.
> 
> scsi sets blk_queue_segment_boundary() then gets out of the way, for the 
> most part.  BIOVEC_SEG_BOUNDARY() is the macro that accesses this. Trace 
> back and forth from there.  You will probably run into a call to 
> blk_recount_segments() in __bio_add_page(), or maybe you'll check the 
> seg boundary from another path.

Yeah, I'm familiar with that part, and thanks for the note about SGIO.

So therefore, code to manage the dma_boundary is NOT necessary in sata drivers. 
Right?  Currently we have in sata_mv.c:

	MV_DMA_BOUNDARY = 0xffff;
                 while (sg_len) {
                         offset = addr & MV_DMA_BOUNDARY;
                         len = sg_len;
                         if ((offset + sg_len) > 0x10000)
                                 len = 0x10000 - offset;
                 ...


That whole block should be able to go, then.

Cheers