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

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Date:	Sat, 12 May 2012 14:13:07 +0530
From:	Thomas Abraham <thomas.abraham@...aro.org>
To:	Olof Johansson <olof@...om.net>
Cc:	linux-mmc@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	cjb@...top.org, grant.likely@...retlab.ca, rob.herring@...xeda.com,
	linux-samsung-soc@...r.kernel.org, kgene.kim@...sung.com,
	patches@...aro.org
Subject: Re: [PATCH 3/7] mmc: dw_mmc: add device tree support

On 12 May 2012 12:37, Olof Johansson <olof@...om.net> wrote:
> Hi,
>
> On Thu, May 10, 2012 at 3:15 AM, Thomas Abraham
> <thomas.abraham@...aro.org> wrote:
>> Hi Olof,
>>
>> On 2 May 2012 23:37, Olof Johansson <olof@...om.net> 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.

Thanks,
Thomas.

>
>
> -Olof
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