Re: [S] Re: [linux-uwb] packet size problem

[Alan Stern]

On Wed, 11 Jun 2008, Jens Axboe wrote:

> > Jens, this is a question for you.  How come we're getting an SG element
> > whose lenth is 3584 when the request_queue's dma_alignment mask is set
> > to 1023?  Is dma_alignment not the right parameter to set?
> 
> dma_alignment mask is the buffer address alignment, so they are not
> completely the same.

Well then, put it this way: We don't care particularly about the
address alignment as such, but we do need the buffer length to be a
multiple of 1024 for all but the last element in the SG list.  Is there
a better way to accomplish this?

> But it does sound odd, since you would then be
> spanning two pages for that sg element. Is this before or after dma
> mapping the sg table?

Both.

Alan Stern

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