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

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Message-ID: <Pine.LNX.4.44L0.0806111112370.3218-100000@iolanthe.rowland.org>
Date:	Wed, 11 Jun 2008 11:16:49 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Jens Axboe <jens.axboe@...cle.com>
cc:	AntonioLin <antonio.lin@...ormicro.com>,
	David Vrabel <david.vrabel@....com>,
	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [S] Re: [linux-uwb] packet size problem

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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