linux-kernel - Re: [PATCH v2 1/6] ARM: brcmstb: add infrastructure for ARM-based Broadcom STB SoCs

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Date:	Thu, 5 Dec 2013 21:07:06 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	Marc Carino <marc.ceeeee@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Christian Daudt <bcm@...thebug.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/6] ARM: brcmstb: add infrastructure for ARM-based Broadcom STB SoCs

On Thursday 05 December 2013, Florian Fainelli wrote:
> 2013/12/3 Arnd Bergmann <arnd@...db.de>:
> >
> >> +     addr = ioremap(BPHYSADDR(BCHP_IRQ0_IRQEN), sizeof(u32));
> >> +     writel_relaxed(BCHP_IRQ0_IRQEN_uarta_irqen_MASK
> >> +             | BCHP_IRQ0_IRQEN_uartb_irqen_MASK
> >> +             | BCHP_IRQ0_IRQEN_uartc_irqen_MASK, addr);
> >> +     iounmap(addr);
> >
> > What does this part do? Isn't that something that should have been set
> > up by the boot loader?
> 
> The bootloader will typically use the UART in busy-looping mode and
> not rely on interrupts, also the bootloader currently does not know
> much about how many UARTs there are in the system and how they are
> going to be used.

Well, it should at least know how many ports are wire up and be able
to set them up to a working state.

> One possible way to solve this would be to write a very small irqchip
> driver which only implements the "irq_enable" method to allow these
> interrupts to be forwarded to the GIC. Somewhere in the Device Tree we
> would have an interrupt-map property which describes the mapping
> between the bits in BCHP_IRQ0_IRQEN and their corresponding
> peripherals (UARTA, B, C).
> 
> Would that work?

I think that would work, but it's getting into the overdesign territory.
Can you clarify why this register exists in the first place and what
makes it necessary to set it up? Are there similar registers for all
other IRQs?

	Arnd
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