Re: [PATCH v5 6/9] ARM: shmobile: Add PCIe device tree nodes for R8A7790

[Arnd Bergmann <arnd@arndb.de>]

On Wednesday 26 March 2014 09:55:04 Phil.Edworthy@renesas.com wrote:
> Hi Arnd,
> 
> On: 25/03/2014 18:42, Arnd wrote:
> > Subject: Re: [PATCH v5 6/9] ARM: shmobile: Add PCIe device tree nodes 
> for R8A7790
> > 
> > On Tuesday 25 March 2014 16:56:41 Phil Edworthy wrote:
> > > +               /* Map all possible DDR as inbound ranges */
> > > +               dma-ranges = <0x42000000 0 0x40000000 0 0x40000000 0 
> 0x80000000
> > > +                             0x43000000 1 0x80000000 1 0x80000000 0 
> 0x80000000>;
> > 
> > Typo: 0x43000000 should be 0x42000000 I guess.
> I used 0x43000000 as this is a 64-bit type. The OF PCI range code 
> currently treats both 32 and 64-bit types the same way, but I thought it 
> would be good to set this in case we ever need to use it.

Ah, I forgot about the space identifier. It looks correct then, but
it seems  a little strange to use a 32-bit identifier in one case
and a 64-bit one in the other.

> > Since you control the mapping, I wonder if you could also do this as
> > 
> >                dma-ranges = <0x42000000 0 0x00000000 0 0x40000000 0 
> 0x80000000
> >                              0x43000000 0 0x80000000 1 0x80000000 0 
> 0x80000000>;
> > 
> > i.e. map all the RAM into PCI bus addresses below the 32-bit boundary.
> > This would be really nice from the perspective that now all PCI
> > devices could access all of RAM without using an IOMMU or the
> > relying on 64-bit master capability.
> > 
> > The downside of this is that you'd probably need a custom dma_map_ops
> > wrapper.
> Since the OF PCi range code treats both 32 and 64-bit types the same way, 
> my PCIe driver only creates 64-bit mappings. In addition, the PCIe 
> controller has to use a 64-bit mapping for anything over 2GiB. Based on 
> this, I think it's sensible to leave the mappings as 1-to-1.

I'm not following, sorry. What is the hardware requirement in the
controller?

	Arnd