Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751566Ab3HOVPe (ORCPT ); Thu, 15 Aug 2013 17:15:34 -0400 Received: from devils.ext.ti.com ([198.47.26.153]:46490 "EHLO devils.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751133Ab3HOVPc (ORCPT ); Thu, 15 Aug 2013 17:15:32 -0400 Message-ID: <520D44C5.6080205@ti.com> Date: Thu, 15 Aug 2013 17:14:45 -0400 From: Santosh Shilimkar User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: Linus Walleij CC: Sricharan R , Tony Lindgren , Nishanth Menon , "linux-kernel@vger.kernel.org" , "devicetree-discuss@lists.ozlabs.org" , "linux-doc@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Linux-OMAP , Russell King - ARM Linux , Rajendra Nayak , Felipe Balbi , Thomas Gleixner , Grant Likely Subject: Re: [PATCH 1/3] misc: Add crossbar driver References: <51E83A4F.5080904@ti.com> <51ED2385.60108@ti.com> <51ED5C66.1010407@ti.com> <51EFFBE1.4090505@ti.com> <51F0031B.1050307@ti.com> <51F00530.9090703@ti.com> <51F02069.3050207@ti.com> <51F0223E.4050008@ti.com> <51F0240F.3050507@ti.com> <20130813081003.GU7656@atomide.com> <520A02BA.4090805@ti.com> <520D398D.9040806@ti.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2702 Lines: 66 On Thursday 15 August 2013 04:51 PM, Linus Walleij wrote: > On Thu, Aug 15, 2013 at 10:26 PM, Santosh Shilimkar > wrote: >> On Thursday 15 August 2013 04:01 PM, Linus Walleij wrote: >>> On Tue, Aug 13, 2013 at 11:56 AM, Sricharan R wrote: >>> >>>> 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. >>> >>> I think it is better to use irqchip. >>> >> Did you happen to read the thread why irqchip is in-appropriate >> for such an IP. > > Sorry I don't understand what thread that is... can you point me there? > My previous statement on this issue what this: > http://marc.info/?l=linux-kernel&m=137442541628641&w=2 > It was discussed in couple of threads but the main point was the need of a link needed for the irqchip. >> As I said earlier, an IRQ-chip always need a >> real IRQ link (even for the chained one) to the primary irqchip. >> >> This IP is just dummy IP makes the connections for the primary >> irqchip(read GIC). And its use only limited to make the >> connection between the peripheral IRQ event to the GIC IRQ line. >> >> I don't see how you can make this happen with an irqchip >> infrastructure. > > I think my post above describes this. > Sorry for being dumb but I don't think cascaded irqchip examples like GPIO and cross-bars are same. If you take an example of GPIO irqchip, it always have a physical connection even if it is 1 IRQ line for (32 logical/sparse IRQs). That goes with other MFD examples too. So may be I am still missing something in your proposal. >>> I don't see any way to really abstract this pretty simple crossbar >>> for reuse across subsystems. >>> >> This exactly the reason, i am against idea of over-engineering the >> simple IP whose only job is to make the physical wire connection >> in software where as this is generally done in RTL by default on >> most of the SOCs. > > Well, it was made accessible by software, and if someone has a > usecase that requires this do be done dynamically, i.e. not just > being set up by firmware and never touched, and that use case > is valid, then I guess we need to do something... > > I think it was mentioned in the thread that there is really such > a usecase? > Actually there is no practical usecase but one but one can manufacture it ;-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/