linux-kernel - Re: [PATCH v5 1/3] initialize each mbigen device node as a interrupt controller.

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Date:	Sun, 11 Oct 2015 12:03:31 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"majun (F)" <majun258@...wei.com>, <Catalin.Marinas@....com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <Will.Deacon@....com>,
	<mark.rutland@....com>, <jason@...edaemon.net>,
	<lizefan@...wei.com>, <huxinwei@...wei.com>,
	<dingtianhong@...wei.com>, <zhaojunhua@...ilicon.com>,
	<liguozhu@...ilicon.com>, <xuwei5@...ilicon.com>,
	<wei.chenwei@...ilicon.com>, <guohanjun@...wei.com>,
	<wuyun.wu@...wei.com>, <guodong.xu@...aro.org>,
	<haojian.zhuang@...aro.org>, <zhangfei.gao@...aro.org>,
	<usman.ahmad@...aro.org>, <klimov.linux@...il.com>
Subject: Re: [PATCH v5 1/3] initialize each mbigen device node as a
 interrupt controller.

On Sun, 11 Oct 2015 11:54:49 +0200
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Sat, 10 Oct 2015, Marc Zyngier wrote:
> > On Sat, 10 Oct 2015 17:01:32 +0800
> > "majun (F)" <majun258@...wei.com> wrote:
> > > But there is a problem If i make the structure like you said.
> > > 
> > > For example, my hardware structure likes below:
> > > 
> > > uart ------> mbigen --> ITS-pMSI --> ITS --> GIC
> > >      virq1
> > > 
> > > virq1 means the virq number allocted by irq_of_parse_and_map() function
> > > when system parse the uart dts node in initializing  stage.
> > > 
> > > To create a ITS device, I need to call msi_domain_alloc_irqs() function
> > > in my mbigen alloc function.
> > > 
> > > In this function, a new virq number(named as virq2 ) which different from
> > > virq1 is allocated.
> > > So, this is a big problem.
> > 
> > I think I see what your problem is:
> > - The wired interrupt (uart -> mbigen) is allocated through DT (and
> >   must be available early, because of of_platform_populate),
> > - The MSI (mgigen -> ITS) is dynamic (and allocated much later,
> >   because the device model kicks in after irqchip init, and we cannot
> >   allocate MSIs without a device).
> 
> Why do we need that wired interrupt at all? 
> 
> We can make mbigen the 'msi-parent' of the device and let the
> msi_domain_ops::msi_prepare() callback figure out the actual wiring
> through device->fwnode.

That's because the device behind the mbigen can't do any MSI at all.
Think of a 8250 uart, for example.

If we make the mbigen the msi-parent of the uart, then we need to teach
the 8250 driver to request MSIs. It also means that the DT doesn't
represent the HW anymore (this wired interrupt actually exists).

Thanks,

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