Message-ID: <218865f9-ac06-ba47-287e-cff188957736@arm.com>
Date:   Wed, 26 Jul 2017 14:50:28 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] irqchip: create a Kconfig menu for irqchip drivers

On 26/07/17 14:14, Masahiro Yamada wrote:
> 2017-07-26 19:37 GMT+09:00 Marc Zyngier <marc.zyngier@....com>:
>> On 26/07/17 11:18, Masahiro Yamada wrote:
>>> Hi Marc,
>>>
>>>
>>> 2017-07-26 17:04 GMT+09:00 Marc Zyngier <marc.zyngier@....com>:
>>>> On 26/07/17 05:03, Masahiro Yamada wrote:
>>>>> Some irqchip drivers have a Kconfig prompt.  When we run menuconfig
>>>>> or friends, those drivers are directly listed in the "Device Drivers"
>>>>> menu level.  This does not look nice.  Create a sub-system level menu.
>>>>>
>>>>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>>>>> ---
>>>>>
>>>>>  drivers/irqchip/Kconfig | 4 ++++
>>>>>  1 file changed, 4 insertions(+)
>>>>>
>>>>> diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
>>>>> index f1fd5f44d1d4..7b66313a2952 100644
>>>>> --- a/drivers/irqchip/Kconfig
>>>>> +++ b/drivers/irqchip/Kconfig
>>>>> @@ -1,3 +1,5 @@
>>>>> +menu "IRQ chip support"
>>>>> +
>>>>>  config IRQCHIP
>>>>>       def_bool y
>>>>>       depends on OF_IRQ
>>>>> @@ -306,3 +308,5 @@ config QCOM_IRQ_COMBINER
>>>>>       help
>>>>>         Say yes here to add support for the IRQ combiner devices embedded
>>>>>         in Qualcomm Technologies chips.
>>>>> +
>>>>> +endmenu
>>>>>
>>>>
>>>> I'm very reluctant to introduce this. IMHO, interrupt controllers are
>>>> way too low level a thing to let them be selected by the user. They
>>>> really should be selected by the platform that needs them
>>>
>>> This is true for the root irqchip.
>>> Not necessarily true for child irqchips.
>>
>> I dispute that argument. We've been able to make this work so far
>> *without* exposing yet another menu maze to the user. What has changed?
> 
> 
> The irqchip maintainers applied drivers
> with user-configurable Kconfig entries.

They are *not* user-selectable, since there is *NO* menu entry. *You*
are making them user-selectable, and I'm objecting to that.

>>>
>>>
>>>> Do you have any example in mind where having a user-selectable interrupt
>>>> controller actually makes sense on its own?
>>>
>>> Yes.
>>>
>>> I see some user-selectable drivers in drivers/irqchip/Kconfig
>>> and I'd like to add one more for my SoCs.
>>>
>>>
>>> This patch:
>>> https://github.com/uniphier/linux/commit/f39efdf0ce34f77ae9e324d9ec6c7f486f43a0ed
>>>
>>> This is really optional, so
>>> I intentionally implemented it as a platform driver
>>> instead of IRQCHIP_DECLARE().
>>
>> I really cannot see how this could be optional. It means that you could
>> end-up in a situation where the drivers for the devices being this
>> irqchip could have been compiled in, but not their interrupt controller.
>> How useful is that?
> 
> In my case, the assumed irq consumer is GPIO.
> 
> If the irq consumer is probed before the irqchip,
> it will be tried later by -EPROBE_DEFER.

> If the irqchip is not compiled at all, right, the irq consumer will not work.
> One possible (and general) solution is to specify "depends on" correctly
> between the provider and the consumer.

Exactly. It has to be selected either by the platform Kconfig, or
whatever is wired onto this irqchip.

>>> Looks like irq-ts4800.c, irq-keystone.c are modules as well.
>>
>> They are directly selected by their respective defconfig.
> 
> 
> Are you sure?
> 
> As far as I see, they are not selected by anyone.
> 
> 
> $ git grep 'TS4800_IRQ\|KEYSTONE_IRQ'
> arch/arm/configs/keystone_defconfig:CONFIG_KEYSTONE_IRQ=y
> arch/arm/configs/multi_v7_defconfig:CONFIG_KEYSTONE_IRQ=y

And what is that if not a selection?

> drivers/irqchip/Kconfig:config TS4800_IRQ
> drivers/irqchip/Kconfig:config KEYSTONE_IRQ
> drivers/irqchip/Makefile:obj-$(CONFIG_TS4800_IRQ)               += irq-ts4800.o
> drivers/irqchip/Makefile:obj-$(CONFIG_KEYSTONE_IRQ)             +=
> irq-keystone.o
> 
> 
> 
> defconfig just provides a default value.

That's the platform maintainer's problem, not mine.

> 
> Users are allowed to disable the option from menuconfig.

No. They are allowed to change what makes sense, and leaving them in
control of the irqchips doesn't make any sense *at all*.

>> On arm64,
>> which is what I expect you driver targets, you should simply select it
>> in your platform entry.
> 
> OK, assuming your clain is correct,
> we have 5 suspicious entries in drivers/irqchip/Kconfig.
> 
> 
> config JCORE_AIC
>         bool "J-Core integrated AIC" if COMPILE_TEST
> 
> config TS4800_IRQ
>         tristate "TS-4800 IRQ controller"
> 
> config KEYSTONE_IRQ
>         tristate "Keystone 2 IRQ controller IP"
> 
> config EZNPS_GIC
>         bool "NPS400 Global Interrupt Manager (GIM)"
> 
> config QCOM_IRQ_COMBINER
>         bool "QCOM IRQ combiner support"
> 
> 
> 
> The prompt strings make the entries visible in menuconfig.
> So, they should be removed.

Not at all. The help string is extremely useful (use the '/' key i9n
menuconfig and search for an entry...), and act as documentation.

> The prompts are pointless if the options are supposed by selected by others.

See above.

> Also, tristate is pointless.
> If they are supposed to be selected by platforms,
> they have no chance to be a module.
> They should be turned into bool (without prompt)
> 
> Is this what you mean?

Among other things, yes.

	M.
-- 
Jazz is not dead. It just smells funny...

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