Re: [PATCH 1/3] gpio: brcmstb: have driver register during subsys_initcall()

[Jim Quinlan <jim2101024@xxxxxxxxx>]

Hi, sorry I am late to this thead.  Our brcmstb PCIe code is using
platform_driver_probe() which does not tolerate EPROBE_DEFER. Also, I
do not see any "cost" associated with having gpio-brcmstb.c using
subsys_initcall(); in fact, I see 33 gpio-*.c files that use
subsys_initcall().  Thanks, Jim

On Thu, Jan 7, 2016 at 1:12 PM, Florian Fainelli <f.fainelli@xxxxxxxxx> wrote:
> On 06/01/16 22:05, Gregory Fong wrote:
>> Hello Florian and Jim,
>>
>> On Wed, Jan 6, 2016 at 10:55 AM, Florian Fainelli <f.fainelli@xxxxxxxxx> wrote:
>>> From: Jim Quinlan <jim2101024@xxxxxxxxx>
>>>
>>> Because regulators are started with subsys_initcall(), and gpio references may
>>> be contained in the regulators, it makes sense to start the brcmstb-gpio's with
>>> a subsys_initcall(). The order within the drivers/Makefile ensures that the
>>> gpio initialization happens prior to the regulator's initialization.
>>>
>>> We need to unroll module_platform_driver() now to allow this and have custom
>>> exit and init module functions to control the initialization level.
>>
>> If gpio pins are needed for a regulator to come up, wouldn't it be
>> better to handle this using deferred probe instead of initcall-based
>> initialization?  Deferred probe has its problems, but I was under the
>> impression that it's the encouraged way to resolve these sort of
>> initialization order issues.
>
> To give you some more context associated with this change, we now have
> some boards which have GPIO-connected regulators to turn on/off PCIe
> endpoint devices. In the downstream kernel, and with lack of a better
> solution for now, we ended-up having the PCIE Root Complex driver to
> claim these regulator, and flip them on shortly before attempting a bus
> scan.
>
> If we used deferred probing, I am assuming the sequence of events could
> go like this:
>
> - PCIe driver gets initialized, looks for regulators, cannot get a
> handle on them, gets EPROBE_DEFER (arch_initcall right now)
> - regulator subsystem gets initialized, does not have a valid GPIO
> provider driver yet, returns EPROBE_DEFER (subsys_initcall)
> - GPIO provider (gpio-brcmstb) finally gets probed and registered,
> regulator get registered and available, PCIe RC driver can now use them
> and power on the PCIE end point (module_initcall)
>
> I suppose this might be working actually, let me go back to the white
> board and look at this with Jim.
> --
> Florian
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