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

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Date:	Tue, 13 Aug 2013 15:26:10 +0530
From:	Sricharan R <r.sricharan@...com>
To:	Tony Lindgren <tony@...mide.com>
CC:	Santosh Shilimkar <santosh.shilimkar@...com>,
	Nishanth Menon <nm@...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>,
	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

Hi Tony,

On Tuesday 13 August 2013 01:40 PM, Tony Lindgren wrote:
> * Santosh Shilimkar <santosh.shilimkar@...com> [130724 12:06]:
>> 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 ;-)
> Sorry for the delay on this, I think the best way to set this up
> is as a separate drivers/irqchip controller. Then just map the
> configured interrupts for the board with interrupt-map and
> interrupt-map-mask binding. No need to stuff all the SoC specific
> maps to the .dts, just the ones used for the board.
>
> Regards,
>
> Tony
>  
 Initially irqchip was discussed, but we also have a DMA crossbar
 to map the dma-requests. Since both irq/dma crossbars should be handled,
 pinctrl was suggested as the appropriate place to handle this.

Regards,
 Sricharan
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