linux-kernel - Re: [PATCH v2 6/9] irqchip / gic: Add stacked irqdomain support for ACPI based GICv2 init

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Date:	Tue, 30 Jun 2015 13:17:14 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Hanjun Guo <hanjun.guo@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>
CC:	Jason Cooper <jason@...edaemon.net>,
	Will Deacon <Will.Deacon@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Arnd Bergmann <arnd@...db.de>,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Olof Johansson <olof@...om.net>, Wei Huang <wei@...hat.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [PATCH v2 6/9] irqchip / gic: Add stacked irqdomain support for
 ACPI based GICv2 init

On 30/06/15 12:50, Hanjun Guo wrote:
> Hi Marc,
> 
> On 06/29/2015 04:39 PM, Marc Zyngier wrote:
>> On 27/06/15 04:52, Hanjun Guo wrote:
>>> On 06/24/2015 01:38 AM, Lorenzo Pieralisi wrote:
>>>> On Tue, Jun 23, 2015 at 04:11:38PM +0100, Hanjun Guo wrote:
> [...]
>>>>
>>>>>>>     	for (i = 0; i < nr_irqs; i++)
>>>>>>>     		gic_irq_domain_map(domain, virq + i, hwirq + i);
>>>>>>> @@ -945,11 +952,11 @@ void __init gic_init_bases(unsigned int gic_nr, int irq_start,
>>>>>>>     		gic_irqs = 1020;
>>>>>>>     	gic->gic_irqs = gic_irqs;
>>>>>>>
>>>>>>> -	if (node) {		/* DT case */
>>>>>>> +	if (node || !acpi_disabled) {		/* DT or ACPI case */
>>>>>>>     		gic->domain = irq_domain_add_linear(node, gic_irqs,
>>>>>>>     						    &gic_irq_domain_hierarchy_ops,
>>>>>>>     						    gic);
>>>>
>>>> I think this is a bit more worrying, I mean passing a NULL node pointer to
>>>> the irqdomain layer which basically means you are booting out of ACPI
>>>
>>> I'm little confused here, would you mind explaining more for your
>>> worrying? To me, node pointer is optional and it's ok for ACPI
>>> case.
>>>
>>>> (for you, if that's true for the irq_domain_add_linear implementation
>>>> that's another story), the node pointer should be optional but you
>>>> need feedback from IRQ layer maintainers here.
>>>
>>> Sure.
>>
>> Frankly, I'd really like to see ACPI using the "node" parameter for
>> something useful. This would save having to cache pointers all over the
>> place, will make find_irq_host() work as expected... etc.
>>
>> See the comment at the top of linux/irqdomain.h :
>>
>> "... This code could thus be used on other architectures by replacing
>> those two by some sort of arch-specific void * "token" used to identify
>> interrupt controllers."
> 
> To init GIC in ACPI, we can only use the table entry pointer as
> the token, but the ACPI static tables are early mem/io remapped
> memory at boot stage, and it will be not available after boot,
> also we need muti types of MADT enties to init GIC (GICC and GICD
> for GICv2, GICC or GICR and GICD for GICv3), not as DT, just
> one single node to include all the information needed to init
> the GIC.

A single pointer would be enough, you don't need all of them.

> We use ACPI handle for devices as node for DT when the namespace
> is available, but that's pretty late in the boot stage which GIC,
> SMP and timers were already initialized, so ACPI handle can not
> use as the token too.
> 
> I see multi places just pass NULL as the pointer directly for
> irq_domain_add_linear() which works fine, and for ACPI, we tested
> this patch and also it works.

Yes it works. But you're reinventing the wheel by keeping references
outside of the normal framework, which is simply going to make the code
more difficult to maintain in the long run.

Putting NULL as the device_node parameter really means "this is a domain
I don't need to look up later". In your case, you will have to lookup
that domain, all the time. You're just doing it in your own little
corner, which is what bothers me.

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