Re: Lack of suspend/resume/shutdown ordering between GPIO providers and consumers

From: Grygorii Strashko
Date: Wed Apr 25 2018 - 15:11:07 EST

On 04/25/2018 01:57 PM, Florian Fainelli wrote:
> On 04/25/2018 11:47 AM, Grygorii Strashko wrote:
>> On 04/25/2018 01:29 PM, Florian Fainelli wrote:
>>> On 04/25/2018 11:06 AM, Grygorii Strashko wrote:
>>>> On 04/24/2018 05:58 PM, Florian Fainelli wrote:
>>>>> Hi Linus, Rafael, all
>>>>> Our GPIO controller driver: gpio-brcmstb.c has a shutdown callback
>>>>> which
>>>>> gets invoked when the system is brought into poweroff aka S5. So far so
>>>>> good, except that we also wish to use gpio_keys.c as a possible wake-up
>>>>> source, so we may have a number of GPIO pins declared as gpio-keys that
>>>>> allow the system to wake-up from deep slumber.
>>>>> Recently we noticed that we could easily get into a state where
>>>>> gpio-brcmstb.c::brcmstb_gpio_shutdown() gets called first, and then
>>>>> gpio_keys.c::gpio_keys_suspend() gets called later, which is too
>>>>> late to
>>>>> have the enable_irq_wake() call do anything sensible since we have
>>>>> suspend its parent interrupt controller before. This is completely
>>>>> expected unfortunately because these two drivers are both platform
>>>>> device instances with no connection to one another except via Device
>>>>> Tree and the use of the GPIOLIB APIs.
>>>> You can take a look at device_link_add() and Co.
>>> OK, though that requires a struct device references, so while I could
>>> certainly resolve the device_node -> struct device that corresponds to
>>> the GPIO provider , that poses a number of issues:
>>> - not all struct device_node have a corresponding struct device
>>> reference (e.g: clock providers, interrupt controllers, and possibly
>>> other custom drivers), though in this case, they most likely do have one
>>> - resolving a struct device associated with a struct device_node is
>>> often done in a "bus" specific way, e.g: of_find_device_by_node(), so if
>>> the GPIO provider is e.g: i2c_device, pci_device etc. etc. this might
>>> not work that easily
>>> I think this is what Dmitry just indicated in his email as well.
>>>> But it's little bit unclear what exactly you have issue with:
>>>> - shutdown
>>>> - suspend
>>>> above are different (at least as it was before) and gpio-brcmstb.c
>>>> ÂÂbrcmstb_gpio_shutdown() should not be called as part of suspend !?
>>>> may be you mean brcmstb_gpio_suspend?
>>> The issue exists with shutdown (through the use of "poweroff"), that is
>>> confirmed, but I cannot see how it does not exist with any suspend state
>>> as well, for the same reason that the ordering is not strictly enforced.
>> Sry, but it still required some clarification :( - poweroff calls
>> device_shutdown() which, in turn, should not call .suspend(), so
>> how have you got both .shutdown() and .suspend() callbacks called during
>> poweroff? Am I missing smth?
> You are missing me telling you the whole story, sorry I got confused,
> but you are absolutely right these are separate lists and on
> poweroff/shutdown only ->shutdown() is called. What I had missed in the
> report I was submitted was that there was a .shutdown() callback being
> added to gpio_keys.c, which of course, because it's an Android based
> project is not in the upstream Linux kernel.
> The problem does remain valid though AFAICT. Thanks Grygorii!

Thanks. But that means you should not see this problem :(
There is devices_kset_move_last() call in really_probe() which moves probed dev
at the end of kset, and gpio_keys should never be probed before gpio-brcmstb because
both devm_fwnode_get_gpiod_from_child() and devm_gpio_request_one() expected to return
-EPROBE_DEFER otherwise.

Theoretically issue still might happen with suspend.