Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752816AbXKNHUE (ORCPT ); Wed, 14 Nov 2007 02:20:04 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751028AbXKNHTw (ORCPT ); Wed, 14 Nov 2007 02:19:52 -0500 Received: from smtp103.sbc.mail.mud.yahoo.com ([68.142.198.202]:35992 "HELO smtp103.sbc.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750998AbXKNHTv (ORCPT ); Wed, 14 Nov 2007 02:19:51 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=pacbell.net; h=Received:X-YMail-OSG:From:To:Subject:Date:User-Agent:Cc:References:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding:Content-Disposition:Message-Id; b=odXBF9Yu9fH+0Gzc2fwELg9DoD3iZy8D2zKRxUotG0HVvQEb+LWlhWfmWX9tBMCpXPjgYyVNvtNwEBvOFIdGr1lC56DxuubUdvpGRnpFNsgk0Hf2/iX6SUIN1eyIPi5gSFWn/x1RNJAjbdPIJe28VEM8vRXAUGbwYch/iY8cPec= ; X-YMail-OSG: fI.1DWYVM1mTEovTisz0DqsnfsfeKFI6uoCPWyW4szr8rfhQuvCHtlLoyXLGNtdEYxL6ttv8eQ-- From: David Brownell To: "eric miao" Subject: Re: [patch/rfc 1/4] GPIO implementation framework Date: Tue, 13 Nov 2007 23:19:47 -0800 User-Agent: KMail/1.9.6 Cc: "Linux Kernel list" , "Felipe Balbi" , "Bill Gatliff" , "Haavard Skinnemoen" , "Andrew Victor" , "Tony Lindgren" , "Jean Delvare" , "Kevin Hilman" , "Paul Mundt" , "Ben Dooks" References: <200710291809.29936.david-b@pacbell.net> <200711132036.14927.david-b@pacbell.net> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200711132319.48821.david-b@pacbell.net> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1294 Lines: 37 > > > struct gpio_desc { > > > struct gpio_chip *chip; > > > unsigned is_out:1; > > > + unsigned requested:1; > > > +#ifdef CONFIG_DEBUG_FS > > > + const char *requested_str; > > > +#endif > > > > Note that this means (on typical 32-bit embedded hardware) > > twelve bytes per GPIO, which if you assume 256 GPIOs means > > an extra 3 KB static memory compared to the patch I sent. Actually, 2K is a more accurate number -- ignore DEBUG_FS. > Note this reduces the memory in gpio_chip, so it consumes almost same > memory as the patch you sent. No; the amount of space shaved from a typical (32-bit banks) gpio_chip is *exactly* the cost of one gpio_desc: two words. In one case, two bitmaps. In the other, a pointer, two bits, and internal struct padding. So unless each bank has only a single GPIO, this approach does cost more memory. Both for the extra memory associated with each gpio_chip that's used, and for unused gpio_desc. That's not necessarily a bad thing, though it's always worth avoiding bloat. - Dave - 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/