Subject: [PATCH v12 11/31] documentation: iommu: add binding document of Exynos System MMU

From: [email-masked] (Stephen Warren)
Date: Mon, 28 Apr 2014 11:52:24 -0600

On 04/28/2014 05:18 AM, Thierry Reding wrote:
> On Mon, Apr 28, 2014 at 12:56:03PM +0200, Arnd Bergmann wrote:
...
>> A lot of drivers probably only support one
>> master, so they can just set #iommu-cells=<0>, others might require
>> IDs that do not fit into one cell.
> 
> You mean "#iommu-cells = <1>" for devices that only require one master?
> There still has to be one cell to specify which master. Unless perhaps
> if they can be arbitrarily assigned. I guess even if there's a fixed
> mapping that applies to one SoC generation, it might be good to still
> employ a specifier and have the mapping in DT for flexibility.

#iommu-cells doesn't include the phandle, so if you want the client
references to be:

property = <&iommu>;

then that's #iommu-cells=<0>, whereas:

property = <&iommu N>;

is #iommu-cells=<1>.