From: Roland Dreier <rdreier@cisco.com>
To: Steve Wise <swise@opengridcomputing.com>
Cc: Benjamin Herrenschmidt <bherren@au1.ibm.com>,
linux-kernel@vger.kernel.org,
OpenFabrics General <general@lists.openfabrics.org>,
Wen Xiong <wenxiong@us.ibm.com>
Subject: Re: [ofa-general] iommu dma mapping alignment requirements
Date: Thu, 20 Dec 2007 10:07:39 -0800 [thread overview]
Message-ID: <adalk7pz1ck.fsf@cisco.com> (raw)
In-Reply-To: <476AA2E2.5010007@opengridcomputing.com> (Steve Wise's message of "Thu, 20 Dec 2007 11:14:10 -0600")
> It appears that my problem boils down to a single host page of memory
> that is mapped for dma, and the dma address returned by dma_map_sg()
> is _not_ 64KB aligned. Here is an example:
> My first question is: Is there an assumption or requirement in linux
> that dma_addressess should have the same alignment as the host address
> they are mapped to? IE the rdma core is mapping the entire 64KB page,
> but the mapping doesn't begin on a 64KB page boundary.
I don't think this is explicitly documented anywhere, but it certainly
seems that we want the bus address to be page-aligned in this case.
For mthca/mlx4 at least, we tell the adapter what the host page size
is (so that it knows how to align doorbell pages etc) and I think this
sort of thing would confuse the HW.
- R.
next prev parent reply other threads:[~2007-12-20 18:17 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-20 17:14 iommu dma mapping alignment requirements Steve Wise
2007-12-20 17:29 ` [ofa-general] " Tom Tucker
2007-12-20 18:07 ` Roland Dreier [this message]
2007-12-20 19:11 ` Steve Wise
2007-12-20 19:29 ` Steve Wise
2007-12-20 20:21 ` Benjamin Herrenschmidt
2007-12-20 21:22 ` Steve Wise
2007-12-20 20:17 ` Benjamin Herrenschmidt
2007-12-20 21:02 ` Steve Wise
2007-12-20 21:26 ` Benjamin Herrenschmidt
2007-12-20 22:12 ` Steve Wise
2007-12-20 23:49 ` Benjamin Herrenschmidt
2007-12-21 4:49 ` Steve Wise
2007-12-21 5:38 ` Benjamin Herrenschmidt
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