Date:	Thu, 12 Nov 2015 14:34:53 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Grygorii Strashko <grygorii.strashko@...com>,
	Jon Hunter <jonathanh@...dia.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 02:29 PM, Grygorii Strashko wrote:
> On 11/12/2015 03:20 PM, Lars-Peter Clausen wrote:
>> 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.
>>
> 
> In general, this is simplest possible solution. More over, if irqchip will have
> dev field PM runtime could be used directly instead of get/put.  
> 
> but.. :( How about problem [d]?
> 

Can you explain why you thing this is a problem? I don't see the issue.
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