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

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Message-ID: <52178D98.8020202@ti.com>
Date:	Fri, 23 Aug 2013 21:58:08 +0530
From:	Sekhar Nori <nsekhar@...com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
CC:	Sricharan R <r.sricharan@...com>, 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>,
	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 8/23/2013 7:08 PM, Santosh Shilimkar wrote:
> On Friday 23 August 2013 04:14 AM, Sekhar Nori wrote:
>> On Friday 23 August 2013 12:23 PM, Sricharan R wrote:
>>> On Friday 23 August 2013 12:06 PM, Sekhar Nori wrote:
>>>> 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.
>>>  Say, peripheral x uses crossbar 1 and specifies this in DT.
>>>  During boot crossbar 1 gets mapped int 10. So if by default
>>> some other crossbar has its interrupt mapped to 10,
>>> then it should be removed.  Instead clear all crossbar registers
>>> once and mark all as free, then  allocate only during request.
>>> Correct ?. In this the free no need to maintain any list.
>>
>> Right, so in my suggestion there is nothing like a "default mapping" and
>> entire 160 GIC interrupt number space is up for grabs. I think this will
>> be much simpler to write and maintain.
>>
>> If you really want to maintain default mapping as far as possible, you
>> can do two passes on the crossbar interrupt numbers requested. Once to
>> assign the default map - for numbers less that 160 - and then look at
>> the free GIC interrupt slots and use those for numbers greater than 160.
>>
> The whole point we are moving to domain is not have any default
> mapping(connection done) at DT level. Rather DT only specifies the
> peripherals and their cross-bar connection ID(i.e cross-bar IRQ line).
> This will be the driver input as a IRQ line from DT. The cross-bar
> driver needs to map any of the free list available on *request* only.

Right, the mapping can be done on request. That will be cleaner.

Thanks,
Sekhar
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