Re: [PATCH v2 1/4] dt: bindings: mmc: Document the practice of using subnodes for slots

[Ulf Hansson <ulf.hansson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On 2 June 2014 10:38, Jaehoon Chung <jh80.chung-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org> wrote:
> On 06/02/2014 05:29 PM, Ulf Hansson wrote:
>> On 1 June 2014 11:23, Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>>> Hi,
>>>
>>>
>>> On 05/31/2014 10:13 PM, Olof Johansson wrote:
>>>>
>>>> On Sat, May 31, 2014 at 12:03 PM, Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>>>> wrote:
>>>>>
>>>>> The following existing MMC host controller bindings use slot subnodes:
>>>>>
>>>>> Documentation/devicetree/bindings/mmc/synopsys-dw-mshc.txt
>>>>> Documentation/devicetree/bindings/mmc/k3-dw-mshc.txt
>>>>> Documentation/devicetree/bindings/mmc/exynos-dw-mshc.txt
>>>>> Documentation/devicetree/bindings/mmc/socfpga-dw-mshc.txt
>>>>> Documentation/devicetree/bindings/mmc/atmel-hsmci.txt
>>>>> Documentation/devicetree/bindings/mmc/rockchip-dw-mshc.txt
>>>>>
>>>>> This commit documents this practice in the standard mmc bindings
>>>>> documentation.
>>>>>
>>>>> Signed-off-by: Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>>>>
>>>>
>>>> There are today only two drivers that use this kind of binding, dw_mmc
>>>> and the at91 one.
>>>
>>>
>>> Correct.
>>>
>>>
>>>> Neither seems to actually ever have been used with
>>>> more than one slot. I doubt anyone building an exynos-based system
>>>> will ever do a multi-slot solution, and it seems that the at91 driver
>>>> doesn't actually handle more than one slot.
>>>>
>>>> I'm personally not that excited about complicating the bindings by
>>>> opening up for this -- I would rather work towards removing the
>>>> concept of slots if it's one of those things that are going to remain
>>>> unused. We have actually been talking about reworking the dw_mmc
>>>> binding to remove the slot concept (and simplify the driver by doing
>>>> so).
>>>
>>>
>>> I'm fine with removing the slot subnode, I added it because of it being
>>> brought up in the powerup sequence discussion. I explicitly asked there
>>> if adding such a subnode level was seen as desirable but nobody
>>> answered :|
>>>
>>> Anyways, either way works for me. I can do a v3 dropping the slot subnode
>>> level again. I would really like to move forward with a decision on how-to
>>> represent non probable info for sdio devices in device nodes. So do you
>>> have any other remarks other then that the slot subnode should be dropped ?
>>> And if not can you please review and ack (*) v3 of this patch-set once
>>> I've send it?
>>>
>>> Chris Ball and Ulf Hansson, what is your take on this, are you willing to
>>> take this patch set? And do you want it with or without the slot subnodes ?
>>
>> I certainly appreciate you working actively on this Hans, I will look
>> into the patchset as soon as I can.
>>
>> I share Olof's view about the slot nodes, we must not add DT bindings
>> that isn't really needed.
>>
>> Regarding the slot subnodes; Jaehoon Chung recently posted a patchset
>> for adding the parsing of it, intended for dwmmc. I withdraw my ack
>> for it, and let's try to go in the other direction instead.
>>
>> [PATCHv3 0/4] mmc: fixed the mmc_of_parse for dwmmc.
>>
>> Thus I suggest we should clean-up host drivers to support only one
>> card per host, and entirely skip the slot concept.
>
> Well, almost platform is used the only one card per host, although some controller is supported the slot concept.
> But we don't know that controller should be used the multi slot per host, in future.
> So I think we can't skip the slot concept.

The mmc core only supports one card per host.

Adding DT bindings for something that seems unlikely to be supported
in future, seems like a bad idea. It's better to add it when/if
needed.

Kind regards
Uffe

>
> Best Regards,
> Jaehoon Chung
>
>>
>> Kind regards
>> Uffe
>>
>>>
>>> Thanks & Regards,
>>>
>>> Hans
>>>
>>>
>>> *) Assuming you don't find any issues
>>
>