linux-kernel - Re: [PATCH 1/3] misc: Add crossbar driver

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Date:	Fri, 23 Aug 2013 12:06:18 +0530
From:	Sekhar Nori <nsekhar@...com>
To:	Sricharan R <r.sricharan@...com>
CC:	Rajendra Nayak <rnayak@...com>, Nishanth Menon <nm@...com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Felipe Balbi <balbi@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux-OMAP <linux-omap@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/3] misc: Add crossbar driver

On Friday 23 August 2013 11:41 AM, Sricharan R wrote:
> Hi,
> On Friday 23 August 2013 10:17 AM, Rajendra Nayak wrote:
>> On Thursday 22 August 2013 05:03 PM, Sricharan R wrote:
>>>  maps crossbar number<->  to interrupt number and
>>>  calls request_irq(int_no, crossbar_handler,..)
>> So will this mapping happen based on some data passed from DT or
>> just based on whats available when the device does a request_irq()?
>>
>> If its based on whats available then I see an issue when you need
>> to remap something thats already mapped by default (and not used)
>> since you run out of all free ones.
> Yes, when done based on what is available then there is a
> problem when we run out of free ones because we do not
> know which one to replace. I was thinking of something like
> this,
>     1) DT would give a list of all free ones, and also if some are
>         mapped as default and not used, mark those also as free.
> 
>      2) While mapping see if it has a default mapping and use it.
>           otherwise, pick from free list.   

Since the entire DT is available to you at boot time, you should be able
to find each node where interrupt-parent = <&crossbar> and then allocate
one of 0-160 GIC interrupt numbers for that node, no? Where would there
be a need for default mapping and remapping? From one the mails in the
thread the crossbar is completely flexible - any of the 320 crossbar
interrupts can be mapped to any of the 160 GIC interrupts.

Any GIC interrupts left after this boot-time scan can be added to an
unused list for use with runtime DT fragments (when that support comes).

Sorry if I misunderstood, but above proposal sounds like maintaining a
separate free interrupt lines list in DT. That will quickly go out of sync.

Thanks,
Sekhar
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