On Fri, Feb 23, 2007 at 06:39:11PM +0100, Jachym Holecek wrote:
> Hello,
> 
> a couple of minor nits:
> 
> # Yorick Hardy 2007-02-23:
> > --- share/man/man9/bus_dma.9.orig	2007-02-23 16:21:58.000000000 +0200
> > +++ share/man/man9/bus_dma.9	2007-02-23 16:33:57.000000000 +0200
> > @@ -777,6 +784,53 @@
> >  .Pp
> >  Returns -1 to indicate failure.
> >  Otherwise, returns an opaque value to be interpreted by the device pager.
> > +.It Fn bus_dmatag_subregion "tag" "min_addr" "max_addr" "newtag" "flags"
> > +Creates a new bus_dma_tag_t in
> > +.Fa newtag
> > +from
> > +.Fa tag
> > +with the added constraint that data will only be transferred to
> > +memory addresses in the range (subregion)
> 
> Aren't they bus addresses, really? On a system with IOMMU, the subregion
> constraint translates to address constraint on the _bus_ side of the
> translation, memory address isn't really restricted.

Yes, these are bus addresses.

> > +.Fa min_addr
> > +to
> > +.Fa max_addr.
> > +The arguments are as follows:
> > +.Bl -tag -width nsegs -compact
> > +.It Fa tag
> > +This is the bus_dma_tag_t passed down from the parent driver via
> > +.Fa \*[Lt]bus\*[Gt]_attach_args .
> > +.It Fa min_addr
> > +The low address constraint for DMA transfers.
> > +This address is included.
> 
> I should've asked earlier how much practical value the lower constraint
> has... No problem keeping it, just curious -- I can't imagine how would
> one need to FUBAR a device to make it unable to transfer below certain
> address.

A single device may not, but one could immagine a bridge between 2 busses with
a fixed offset on addresses ...

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--