Date:	Thu, 12 Nov 2015 14:20:12 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Jon Hunter <jonathanh@...dia.com>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Kevin Hilman <khilman@...nel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-tegra@...r.kernel.org,
	Soren Brinkmann <soren.brinkmann@...inx.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>
Subject: Re: [RFC PATCH 1/2] genirq: Add runtime resume/suspend support for
 IRQ chips

On 11/12/2015 11:59 AM, Jon Hunter wrote:
> 
> On 11/11/15 15:41, Grygorii Strashko wrote:
>> On 11/11/2015 12:13 PM, Jon Hunter wrote:
>>>
>>> On 10/11/15 18:07, Lars-Peter Clausen wrote:
>>>> On 11/10/2015 05:47 PM, Grygorii Strashko wrote:
>>>> [...]
>>>>>> I was trying to simplify matters by placing the resume call in
>>>>>> __setup_irq() as opposed to requested_threaded_irq(). However, the would
>>>>>> mean the resume is inside the bus_lock and may be I should not assume
>>>>>> that I can sleep here.
>>>>>>
>>>>>>> Can you folks please agree on something which is correct and complete?
>>>>>>
>>>>>> Soren I am happy to defer to your patch and drop this. My only comment
>>>>>> would be what about the request_percpu_irq() path in your patch?
>>>>>>
>>>>>
>>>>> I have the same comment here as I asked Soren:
>>>>> 1) There are no restrictions to call irq set_irq_type() whenever,
>>>>> as result HW can be accessed before request_x_irq()/__setup_irq().
>>>>> And this is used quite widely now :(
>>>>>
>>>>
>>>> Changing the configuration of a resource that is not owned seems to be
>>>> fairly broken. In the worst case this will overwrite the configuration that
>>>> was set by owner of the resource.
>>>>
>>>> Especially those that call irq_set_irq_type() directly before request_irq(),
>>>> given that you supply the trigger type to request_irq() which will make sure
>>>> that there are no conflicts and the configure.
>>>>
>>>> This is a bit like calling gpio_set_direction() before you call
>>>> gpio_request(), which will also have PM issues.
>>>
>>> Yes, I agree that this does sound a bit odd, but ...
>>>
>>>>> For example, during OF boot:
>>>>>
>>>>> [a]  irq_create_of_mapping()
>>>>>     - irq_create_fwspec_mapping()
>>>>>       - irq_set_irq_type()
>>>
>>> The above means that if someone calls of_irq_get() (or
>>> platform_get_irq()), before request_irq(), then this will call
>>> irq_create_of_mapping() and hence, call irq_set_irq_type. So should
>>> irq_create_fwspec_mapping() be setting the type in the first place? I
>>> can see it is convenient to do it here.
>>
>> In general there is another option - save OF-flags and pass them to
>> __setup_irq() where they can be processed.
> 
> Right, we could look at doing something like this.
> 
>>>>> or
>> [b]
>>>>> 	irq_set_irq_type(irq, IRQ_TYPE_LEVEL_HIGH);
>>>>> 	irq_set_chained_handler(irq, mx31ads_expio_irq_handler);
>>
>> option: add "flag" parameter to irq_set_chained_handler
>>
>>>>>
>>>>> or
>> [c]
>>>>> 	irq_set_irq_type(alarm_irq, IRQ_TYPE_EDGE_BOTH);
>>>>> 	err = devm_request_irq(&pdev->dev, alarm_irq, fan_alarm_irq_handler,
>>>>> (there are ~200 occurrences of irq set_irq_type in Kernel)
>>>>>
>>>>> 2) if i'm not wrong, the same is valid for irq_set_irq_wake() and irq_set_affinity()
>>>>>
>>>>> I'm not saying all these code is correct, but that what's now in kernel :(
>>>>> I've tried to test Soren's patch with omap-gpio and immediately hit case [a] :.(
>>>>
>>>> All functions for which are part of the public API and for which it is legal
>>>> to call them without calling request_irq() (or similar) first will need to
>>>> have pm_get()/pm_put().
>>>
>>> Right. May be we can look at the various entry points to the chip
>>> operators to get a feel for which public APIs need to be handled.
>>
>>
>> Seems yes. But we need to be very careful with this, some of functions could be
>> called recursively (nested), like:
>> [d]
>> static int pcf857x_irq_set_wake(struct irq_data *data, unsigned int on)
>> {
>> 	...
>> 	error = irq_set_irq_wake(gpio->irq_parent, on);
>>
>>
>> Personally, I have nothing against irq_pm_(get|put) :) and thought about similar things
>> when tried to solve the same problem for omap-gpio driver.
>> But :(, I have to fall back to irq_bus_lock/sync_unlock, because of [a,b,c] - all above
>> APIs surrounded by chip_bus_lock/chip_bus_sync_unlock. ([d] - I've not hit it just because
>> I was lucky).
> 
> I had a quick peek at the omap-gpio driver and I see that internally you
> are using the gpio ref-count to manage RPM and use the bus-lock hooks to
> invoke RPM.
> 
> This can definitely be complex when considering all the potential paths,
> but I think that we need to a look at this from a chip-ops perspective
> because only the chip knows if it is accessible or not. That said, what
> we need to assess is:
> 
> 1. Which chip-ops should ONLY be called after an IRQ has been allocated
>    (eg, enable/disable, mask/unmask, type, etc). These chip-ops should
>    not try to control the chip PM, but should possibly WARN if called
>    when  the chip is not accessible.
> 2. For chip-ops that may be called without allocating an IRQ (eg.
>    bus_lock, irq_suspend, etc), can these be called from an atomic
>    context? If they might be called from an atomic context then these
>    are the chip-ops which will cause problems as we cannot guarantee
>    that all IRQ chips can support irq-safe RPM.

They can't. chip_bus_lock() can sleep, so anything that locks the bus can't
be called from atomic context.

One easy way out might be to always call pm_get/pm_but from
bus_lock,/bus_unlock. This way the chip is guaranteed to be powered up when
accessed happens. In addition pm_get is called when the IRQ is request and
pm_put is called when the IRQ is release, this is to ensure the chip stays
powered when it is actively monitoring the IRQ lines.

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