Subject: RFC: representing sdio devices oob interrupt, clks, etc. in device tree

From: [email-masked] (Arend van Spriel)
Date: Fri, 23 May 2014 16:54:59 +0200

On 05/23/14 15:28, Hans de Goede wrote:
> Hi,
>
> On 05/23/2014 03:21 PM, Arend van Spriel wrote:
>> On 05/23/14 13:50, Hans de Goede wrote:
>>> Hi,
>>>
>>> On 05/23/2014 01:22 PM, Mark Brown wrote:
>>>> On Fri, May 23, 2014 at 11:13:44AM +0200, Hans de Goede wrote:
>>>>
>>>>> Thinking more about this, I would like to make one change to my
>>>>> proposal, the mmc-core should only do power up of child-nodes if
>>>>> they have a compatible of: "simple-sdio-powerup". This way
>>>>> when we add something more complex, we can keep the simple powerup
>>>>> code in the mmc core, keeping what we've already using this working
>>>>> and the mmc core won't respond to the child nodes for more complex
>>>>> devices, so it won't conflict with more complex power-up handling
>>>>> handled by some other driver.
>>>>
>>>> Would it not be better to have this be something in the driver struct
>>>> rather than in the device tree?  Putting a compatible in there would be
>>>> encoding details of the Linux implementation in the DT which doesn't
>>>> seem right especially since these are details we're thinking of changing
>>>> later on.
>>>
>>> The compatible is not a Linux specific thing, it is a marking saying
>>> that something needs to take care of enabling the clks (and whatever
>>> else we will make part of the binding for this compatible), before
>>> scanning the mmc bus.
>>>
>>>> Something like have the driver set flags saying if it wants
>>>> to do complicated things.
>>>
>>> Chicken<->   egg, we won't know which driver to use before we've probed
>>> the mmc bus, and we cannot probe the bus before enabling the clks, etc.
>>
>> The approach I took with brcmfmac is that upon module init I search the DT for "brcm,bcm43xx-fmac" compatible and get the clock and/or gpio resource and enable them before registering the sdio driver. The difficulty is probably when using the driver built-in as the clocks and gpios may not be available yet and we can not rely on deferred probing in module init stage.
>
> I know, and that approach does not work, by the time the brcmfmac loads,
> the mmc core has long probed the mmc bus and decided no one is home.

Ok. That is due to the non-removable property, right? I assumed a mmc 
rescan, which is (supposedly) triggered upon sdio driver registration, 
would subsequently find the device.

Regards,
Arend

> Regards,
> Hans