Re: WARNING: at drivers/ata/libata-core.c:5988 ata_qc_issue()

[Mark Lord <liml@rtr.ca>]

James Bottomley wrote:
> On Thu, 2008-01-24 at 23:29 -0500, Mark Lord wrote:
>> Tejun Heo wrote:
>>> Mark Lord wrote:
>>> ..
>>>> Super!  You've done a great job with this stuff, Tejun!
>>> Thanks but I can't really say nice things about how sata_sil24's
>>> qc_defer() is implemented or how we generally handle command deferring.
>>>  We really need the control at the higher level - request_queue group.
>>> Oh well... I guess you guys will be talking about it over beer again
>>> soon.  :-)
>> ..
>>
>> You too?
>>
>> Another one for those beers, is a way to tell the IOMMU code about
>> physical segment limitations -- so we can stop having to allocate
>> PRD tables 2X as big as necessary in drivers like sata_mv.
> 
> If the IOMMU would observe the queue dma_boundary parameter, is that
> enough?  (it is for the 64k PRD limit).  If so, there are already
> patches in the works to solve this permanently.  If not, could we get
> the requirements to see how it might be done?
..

That sounds like the right thing.

We just have ensure that:

1. single SG/PRD entries never cross a 64KB address boundary.

and these two then naturally follow for free:

2. single SG/PRD entries never exceed 64KB.
3. single SG/PRD entries never cross a 32-bit address boundary.

Are the patches going into 2.6.25 ?
How do we take advantage of them ?

Cheers