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

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Message-ID: <20130814072744.GV7656@atomide.com>
Date:	Wed, 14 Aug 2013 00:27:44 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	Nishanth Menon <nm@...com>, 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>,
	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

* Santosh Shilimkar <santosh.shilimkar@...com> [130813 06:35]:
> On Tuesday 13 August 2013 04:10 AM, 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.
> > 
> Interrupt mask/unmask, really ? Thats like abusing those irqchip
> hooks completely. Your point is to just setup events which we need
> and thats what I also suggested. But the use of irqchip hooks is
> certainly not the right idea since they are for masking/unmasking
> interrupts in running system and not for joining the interrupt
> line which needs to happen once during probe.

Well if it's an interrupt controller. Doing a chained IRQ pinctrl
driver might work too. But yes, the idea with interrupt-map was
to only map what's used rather than have data for each SoC.

Regards,

Tony
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