linux-kernel - Re: [RFC PATCH 0/6] DRIVERS: IRQCHIP: Add support for crossbar IP

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Date:	Tue, 01 Oct 2013 08:48:00 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Sricharan R <r.sricharan@...com>
CC:	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-omap@...r.kernel.org, tglx@...utronix.de,
	linus.walleij@...aro.org, santosh.shilimkar@...com,
	linux@....linux.org.uk, tony@...mide.com, rnayak@...com,
	marc.zyngier@....com, grant.likely@...aro.org, mark.rutland@....com
Subject: Re: [RFC PATCH 0/6] DRIVERS: IRQCHIP: Add support for crossbar IP

On 10/01/2013 06:13 AM, Sricharan R wrote:
> Hi,
> 
> On Monday 30 September 2013 08:39 PM, Rob Herring wrote:
>> On 09/30/2013 08:59 AM, Sricharan R wrote:
>>> Some socs have a large number of interrupts requests to service
>>> the needs of its many peripherals and subsystems. All of the interrupt
>>> requests lines from the subsystems are not needed at the same
>>> time, so they have to be muxed to the controllers appropriately.
>>> In such places a interrupt controllers are preceded by an
>>> IRQ CROSSBAR that provides flexibility in muxing the device interrupt
>>> requests to the controller inputs.
>>>
>>> This series models the peripheral interrupts that can be routed through
>>> the crossbar to the GIC as 'routable-irqs'. The routable irqs are added
>>> in a separate linear domain inside the GIC. The registered routable domain's
>>> callback are invoked as a part of the GIC's callback, which in turn should
>>> allocate a free irq line and configure the IP accordingly. So every peripheral
>>> in the dts files mentions the fixed crossbar number as its interrupt. A free
>>> gic line for that gets allocated and configured when the peripheral's interrupt
>>> is mapped.
>>>
>>> The minimal crossbar driver to track and allocate free GIC lines and configure the
>>> crossbar is added here, along with the DT bindings.
>> Seems like interrupt-map property is what you need here.
>>
>> http://devicetree.org/Device_Tree_Usage#Advanced_Interrupt_Mapping
>>
>> Versatile Express also has an example.
>    OK, but the idea was not to tie up the crossbar<->interrupt numbers at the
>    DTS level, but to assign it dynamically during runtime. This was one of the
>   comments that came up with first crossbar support patches, which was assigning a
>   interrupt line to crossbar number in the DTS and setting it up in crossbar probe.

Is there an actual usecase on a single h/w design that you run out of
interrupts and it is a user decision which interrupts to use?

You could fill in the interrupt-map at run-time. It would have to be
early (bootloader or early kernel init) and can't be at request_irq time.

>     https://lkml.org/lkml/2013/7/18/416
> 
>    Since this approach of assigning in DTS was opposed, we moved to IRQCHIP and
>    that did not go as well. Finally was asked to handle this as a part of GIC driver with
>    a separate domain.
>    
>   http://www.spinics.net/lists/linux-omap/msg97085.html

This has nothing to do with the GIC, so it does not belong there.

Rob

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