linux-kernel - Re: [PATCH 1/2] genirq: add chip_{suspend,resume} PM support to irq

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Date:	Tue, 21 Jul 2015 23:58:01 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Florian Fainelli <fainelli@...adcom.com>
cc:	Florian Fainelli <f.fainelli@...il.com>,
	Brian Norris <computersforpeace@...il.com>,
	Gregory Fong <gregory.0xf0@...il.com>,
	bcm-kernel-feedback-list@...adcom.com,
	linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
	Kevin Cernekee <cernekee@...il.com>,
	Jason Cooper <jason@...edaemon.net>
Subject: Re: [PATCH 1/2] genirq: add chip_{suspend,resume} PM support to
 irq_chip

On Tue, 21 Jul 2015, Florian Fainelli wrote:
> On 21/07/15 14:23, Thomas Gleixner wrote:
> > I just read back on the problem report which was mentioned in the
> > changelog:
> > 
> > "It's not a problem with patch 7, exactly, it's a problem with the
> >  irqchip driver which handles the UART interrupt mask (irq-bcm7120-l2.c).
> >  The problem is that with a trimmed down device tree (such as the one
> >  found at arch/arm/boot/dts/bcm7445-bcm97445svmb.dtb), none of the child
> >  interrupts of the 'irq0_intc' node are described -- we don't have device
> >  tree nodes for them yet -- but we still require saving and restoring the
> >  forwarding mask (see 'brcm,int-fwd-mask') in order for the UART
> >  interrupts to continue operating."
> > 
> > So you are trying to work around a flaw in the device tree by adding
> > random callbacks to the core kernel?
> 
> Not quite, you could have your interrupt controller node declared in
> Device Tree, but have no "interrupts" property referencing it because:
> 
> - the hardware is just not there, but you inherit a common Device Tree
> skleten (*.dtsi)
> - you could have Device Tree overlays which may or may not be loaded as
> a result of finding expansion boards etc...

So if no hardware is there which uses any of those interrupts, then
WHY is it a problem at all?

If it's a requirement that these registers must be restored (once, not
per irq), then I can see that it'd be nice to do that from the core.

Though that core suspend/resume function is generic chip specific. So
it does not make any sense to force it into struct irq_chip because we
have no core infrastructure to deal with it.

Thanks,

	tglx

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