Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754021Ab1DUOYZ (ORCPT ); Thu, 21 Apr 2011 10:24:25 -0400 Received: from mail-pw0-f46.google.com ([209.85.160.46]:40701 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753801Ab1DUOYY (ORCPT ); Thu, 21 Apr 2011 10:24:24 -0400 Date: Thu, 21 Apr 2011 08:24:22 -0600 From: Grant Likely To: Lars-Peter Clausen Cc: Tomoya MORINAGA , linux-kernel@vger.kernel.org, toshiharu-linux@dsn.okisemi.com Subject: Re: Question: GPIO driver how to get irq_base Message-ID: <20110421142422.GC32725@ponder.secretlab.ca> References: <4DAFE62A.105@metafoo.de> <20110421134524.GA32725@ponder.secretlab.ca> <4DB03A4B.9040807@metafoo.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4DB03A4B.9040807@metafoo.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1982 Lines: 46 On Thu, Apr 21, 2011 at 04:08:11PM +0200, Lars-Peter Clausen wrote: > On 04/21/2011 03:45 PM, Grant Likely wrote: > > On Thu, Apr 21, 2011 at 10:09:14AM +0200, Lars-Peter Clausen wrote: > >> [...] > >> > >> In my opinion the best option for expander chips is to allocate a new irq_desc > >> range by calling irq_alloc_descs. It will return the first irq number in the > >> newly allocated range, which will be your irq_base. > > > > Yes, irq_alloc_descs() will give you a range of irqs that the gpio > > expander can use. In many drivers, the irq_base is hard coded in the > > board file and passed in via pdata, but as much as possible I > > recommend avoiding that and letting Linux dynamically allocate the > > irq_base for you. Setting gpio_base to -1 will do this. > > > > The ->to_irq() hook in your driver can translate > > from a gpio number to an irq number for a specific gpio. > > > >> But be aware that this will require SPARSE_IRQ to work. > > > > Why? > > > > Because in a non-SPARSE_IRQ setup all irq_descs will be allocated by default. > See early_irq_init for the non-SPARSE_IRQ case in kernel/irq/irq_desc.c. They'll be allocated, but not all need to be assigned. > > Though platform code could make irq_descs explicitly available byfirst setting > NR_IRQS to a larger number then it actually requires and then call > irq_free_descs for those irqs which are not used by platform code, but using > SPARSE_IRQ is in my opinion the better alternative in this case. On the powerpc platforms, pretty much all irqs are dynamically allocated and SPARSE_IRQ can be either on or off. So, yes, you need to make sure NR_IRQs is large enough if you don't want to use SPARSE, but SPARSE is not a hard requirement. g. -- 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/