Re: [PATCH 1/2] [v4] net: emac: emac gigabit ethernet controller driver

[Rob Herring]

On Fri, Apr 15, 2016 at 10:44 AM, Timur Tabi <timur@xxxxxxxxxxxxxx> wrote:
> Rob Herring wrote:
>>>
>>> >
>>> >         dma-mask = <0 0xffffffff>;
>>> >
>>> >or
>>> >
>>> >         dma-mask = <0xffffffff 0xffffffff>;
>>
>> No. See dma-ranges.
>
>
> How exactly should I use dma-ranges?  I can't find any other drivers that
> queries that property and uses the result to call dma_set_mask.  I thought
> the dma-ranges property is intended to specify address translation.  I don't
> need to translate any address, I just need to know a single number.

You may only care about the size, but the binding has to handle the
more complex case. Here's an example

<0x0 0x2 0x0 0x1 0x0>

dma address 0 (cell 0) maps to cpu (parent) address 0x2_00000000 (cell
1-2) and the range/size is 4G (cell 3-4).

If you have the same base address, then use the same address. The core
will calculate the mask based on the size. IIRC, we also handle ~0 as
a special case to support 4G for #size-cell=1.

Rob