Re: [PATCH 1/6] rapidio: add common mapping APIs for RapidIO memory access

[Kumar Gala]

On Jun 12, 2009, at 8:27 AM, Li Yang wrote:

> On Thu, Jun 11, 2009 at 9:32 PM, Kumar  
> Gala<galak@xxxxxxxxxxxxxxxxxxx> wrote:
> > On Jun 11, 2009, at 4:47 AM, Li Yang-R58472 wrote:
> >
> > > > On May 12, 2009, at 3:35 AM, Li Yang wrote:
> > > >
> > > > > Add the mapping functions used to support direct IO memory  
> > > > > access of
> > > > > rapidIO.
> > > > >
> > > > > Signed-off-by: Zhang Wei <zw@xxxxxxxxxxxxx>
> > > > > Signed-off-by: Li Yang <leoli@xxxxxxxxxxxxx>
> > > >
> > > > Use inbnd/outbnd instead of inb/outb which make one think of
> > > > byte level io accessors.
> > > >
> > > > As I look at this I don't think this is the correct API.  I
> > > > think we should be using the DMA mapping API to hide these
> > > > details.  The concept of mapping like this seems to be more a
> > > > function of FSL's Address translation/mapping unit (ATMU) than
> > > > anything specific to the RIO bus standard.
> > >
> > > This is a separate RIO block level ATMU.  Although it looks like the
> > > system level ATMU, system ATMU doesn't have the knowledge of rapidIO
> > > target device ID.  The mapping need to be dynamic, as it's easy to  
> > > have
> > > more RIO devices than the outbound windows.
> >
> > I understand that.  What I'm saying is the RIO block level ATMU is a
> > Freescale specific detail and not part of any standard RIO bus  
> > programming
> > model.  We have mapping APIs that we can connect to for this via  
> > the DMA API
> > layer.
>
> Ok, I see your point now. Do you mean dma_map_*() for DMA API layer?
> But in my understanding the current dma_map_*() APIs are preparing
> local memory for device to access which is similar to the inbound
> case.  Is it suitable to also use them for mapping device's space for
> CPU access?  Can you give an example of using this API for Address
> Translation and Mapping purpose?

Yes, I meant the dma_map_*() API.  Any system with a true IOMMU uses  
the dma_map_ layer as the way to do address translation.

- k
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/