linux-kernel - Re: [PATCH v2 2/8] irqchip: Supply new driver for STi based devices

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Date:	Thu, 27 Nov 2014 09:55:44 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	jason@...edaemon.net, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, kernel@...inux.com
Subject: Re: [PATCH v2 2/8] irqchip: Supply new driver for STi based devices

On Thu, 27 Nov 2014, Arnd Bergmann wrote:

> On Thursday 27 November 2014 09:29:01 Lee Jones wrote:
> > On Thu, 27 Nov 2014, Arnd Bergmann wrote:
> > > On Thursday 27 November 2014 09:02:55 Lee Jones wrote:
> > > > On Tue, 25 Nov 2014, Arnd Bergmann wrote:
> > > > 
> > > > > On Tuesday 25 November 2014 16:24:59 Lee Jones wrote:
> > > > > 
> > > > > > diff --git a/drivers/irqchip/Kconfig b/drivers/irqchip/Kconfig
> > > > > > index b21f12f..e502f15 100644
> > > > > > --- a/drivers/irqchip/Kconfig
> > > > > > +++ b/drivers/irqchip/Kconfig
> > > > > > @@ -93,6 +93,13 @@ config RENESAS_IRQC
> > > > > >     bool
> > > > > >     select IRQ_DOMAIN
> > > > > >  
> > > > > > +config ST_IRQCHIP
> > > > > > +   bool
> > > > > > +   select REGMAP
> > > > > > +   select MFD_SYSCON
> > > > > > +   help
> > > > > > +     Enables SysCfg Controlled IRQs on STi based platforms.
> > > > > > +
> > > > > 
> > > > > I'm confused by the purpose of this code. It's apparently a driver
> > > > > in drivers/irqchip, the Kconfig symbol contains the string IRQCHIP,
> > > > > yet it doesn't actually register an irq_chip.
> > > > > 
> > > > > Also, the name is a bit too generic, ST has lots of different irqchips,
> > > > > and this apparently isn't even one of them 
> > > > 
> > > > Hmm... now you're going to ask me to remember who I had the
> > > > conversation with that alluded to this as the best location for this
> > > > driver.  Unfortunately, I cannot.  Can you think of a better place to
> > > > put it then?
> > > 
> > > I suspect it's in the right place but should actually be an irqchip
> > > driver. I'm having trouble understanding what this code actually does,
> > > can you you explain the functionality in more detail so we can figure
> > > out what to do with it?
> > 
> > In the simplest terms it's an IRQ unmasker.  A9 Core IRQs are disabled
> > on boot; PMU, CTI (CoreSight), PL310_L2 and EXT.  In order for you to
> > make use of them they need to be unmasked in SYSCFG.
> 
> So you just apply static configuration once, or are there reasons why you
> would mask the interrupts again later?
> 
> If it's all static, why doesn't the boot loader unmask all interrupts before
> starting the kernel?

We'd like to configure them at boot-time, via DT.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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