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

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Date:	Wed, 24 Jul 2013 14:59:27 -0400
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Nishanth Menon <nm@...com>
CC:	Sricharan R <r.sricharan@...com>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux-OMAP <linux-omap@...r.kernel.org>,
	ext Tony Lindgren <tony@...mide.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Rajendra Nayak <rnayak@...com>, Felipe Balbi <balbi@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH 1/3] misc: Add crossbar driver

On Wednesday 24 July 2013 02:51 PM, Nishanth Menon wrote:
> On 07/24/2013 01:43 PM, Sricharan R wrote:
>> On Wednesday 24 July 2013 10:17 PM, Nishanth Menon wrote:
>>> On 07/24/2013 11:38 AM, Santosh Shilimkar wrote:
>>>> On Wednesday 24 July 2013 12:08 PM, Nishanth Menon wrote:
>>>>> That said, maybe a intermediate pinctrl approach might be more pragmatic and less theoretically flexible.
>>>>> an option might be to "statically allocate" default number of interrupts to a domain - example:
>>>>> * GIC IRQ 72->78 allotted to UARTs
>>>>> * pinctrl mapping provided for those but only 6 can be used (rest are marked status="disabled" as default) at any given time (choice of pinctrl option determines GIC interrupt line to use)
>>>>> * All modules will have a pinctrl definition to have a mapping - to avoid bootloader overriding default cross bar setting in ways un-expected by kernel.
>>>>>
>>>>> Does that sound fair trade off?
>>>> This sounds better. That way we can get all the devices in the DT at least.
>>>
>>> Fair enough - if Linus and Tony are still ok with this approach to the problem, seeing a patch series with the effect would be beneficial.
>>>
>>   Ok, i will use this idea of certain number interrupts to groups.
>> Yes on DRA7XX, we have about 160 gic lines and 320 irq crossbar device inputs contending for it.
>> 1:2 and fully arbitrary.  But will we be really exhausting them ?
>>
> Depends on how we allocate :). The default arbitary allocation can be made more logical in your series ofcourse :).
> 
I would just most logical peripherals rather than providing every single
IP connected to cross bar. Otherwise we will end up wth hwmod like
scenario where now started removing the unused stuff because of
maintenance and loc issues ;-)

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