Re: [PATCH 3/7] mmc: dw_mmc: add device tree support

From: Thomas Abraham
Date: Sat May 12 2012 - 04:43:53 EST

On 12 May 2012 12:37, Olof Johansson <olof@xxxxxxxxx> wrote:
> Hi,
> On Thu, May 10, 2012 at 3:15 AM, Thomas Abraham
> <thomas.abraham@xxxxxxxxxx> wrote:
>> Hi Olof,
>> On 2 May 2012 23:37, Olof Johansson <olof@xxxxxxxxx> wrote:
>>> Hi,
>> [...]
>>>> +# Slots: The slot specific information are contained within child-nodes with
>>>> +  each child-node representing a supported slot. There should be atleast one
>>>> +  child node representing a card slot. The name of the slot child node should
>>>> +  be 'slot{n}' where n is the unique number of the slot connnected to the
>>>> +  controller. The following are optional properties which can be included in
>>>> +  the slot child node.
>>> Since we're talking slots / cards on a bus, I think the addressing
>>> model would be useful here. So in the main controller node:
>>>    #address-cells = <1>;
>>>    #size-cells = <0>;
>>> And then each slot would need a reg property and possibly unit address:
>>>   slot {
>>>        reg = <0>;
>>>        ...
>>>   };
>>> (unit addresses on the slots are only needed if they can't be
>>> disambiguated by name, so not needed if you only have one slot).
>> Is the addressing model as described above needed in this case? The
>> address for a slot is not used by the controller driver code and is
>> just a virtual number. It would be sufficient to represent the nodes
>> representing the slots with a unique name.
> The driver has the concept of slot IDs (slot->id struct member), and
> the hardware definitely enumerates them.
> So, I think it makes sense to give a chance to enumerate the slots in
> the device tree. Otherwise, how do you know which one is which on
> hardware? It also opens up the flexibility to have the same name for
> both slots if it makes sense to describe a board that way.

Thanks Olof. Yes, I missed the usage of the id number in the driver. I
will add the slot addressing as you have suggested and repost.


> -Olof
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