linux-kernel - Re: [PATCH] irqchip: create a Kconfig menu for irqchip drivers

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Message-ID: <7595babf-8cc8-9191-cead-09fe955a42af@arm.com>
Date:   Wed, 26 Jul 2017 11:37:36 +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 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?

> 
> 
>> 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?

> Looks like irq-ts4800.c, irq-keystone.c are modules as well.

They are directly selected by their respective defconfig. On arm64,
which is what I expect you driver targets, you should simply select it
in your platform entry.

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