Re: [PATCH] gpiolib: handle probe deferrals better

[Grygorii Strashko <grygorii.strashko@xxxxxx>]

On 04/06/2016 04:39 PM, Linus Walleij wrote:
> On Mon, Apr 4, 2016 at 6:21 PM, Grygorii Strashko
> <grygorii.strashko@xxxxxx> wrote:
> 
>> Below is RFC patch to prove above consent. I've had offlist
>> debugging session with Alexander and He mentioned that this change
>> fixes boot issue for him.
> 
> Thanks for looking into this.
> 
>> Of course, there are some question to discuss:
>> 1) [+] It should sync initialization of GPIOchip and GPIOirqchip
>> 2) [+] This approach requires changes in gpiolib/gpio drivers only, from other side
>> It will require to add fixes all over the Kernel if gpiod_to_irq() will
>> start returning -EPROBE_DEFER.
> 
> Yes, so it will need to be cross-coordinated with IRQ maintainers
> Marc and TGLX.

Seems, I have to study how to be more clear :(
This +/- are all about my RFC patch.
My patch limits the scope of problem to GPIO subsystem/drivers only.
As opposite, if we will touch gpiod_to_irq() - it will affect on whole
kernel.

> 
>> 3) [-] has_irq might need to be initialized by non-DT drivers
> 
> Yes. Every driver in the kernel need to be audited.

With my patch only GPIO drivers need to be checked, especially GPIO
drivers which:
 - are non-DT based;
 - do not use GPIO irq helpers
 - can make IRQ functionality optional using Kconfig/sysfs/module parameters

> 
>> 4) [-] irq_ready might need to be set manually by drivers which do not use GPIO irq
>>     helpers (see change in gpio-mpc8xxx.c)
> 
> Yes. That too. Every driver in the kernel need to be audited.
> 
>> 4) irq_ready access synchronization on SMP? atomic?
> 
> Uhhh.... I don't even understand the question.

in my patch the irq_ready is set from _gpiochip_irqchip_add() and
read from gpiod_request() without any kind of protection and those
two functions can be executed in parallel.

> 
>> job done with commit e6918cd 'gpiolib: handle probe deferrals better'
>> reverted.
> 
> I have taken that out of my tree as well. My naive approach
> doesn't work.
> 


-- 
regards,
-grygorii
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