From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755006Ab3KUS5c (ORCPT ); Thu, 21 Nov 2013 13:57:32 -0500 Received: from avon.wwwdotorg.org ([70.85.31.133]:56180 "EHLO avon.wwwdotorg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753021Ab3KUS5F (ORCPT ); Thu, 21 Nov 2013 13:57:05 -0500 Message-ID: <528E577C.2050506@wwwdotorg.org> Date: Thu, 21 Nov 2013 11:57:00 -0700 From: Stephen Warren User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Hiroshi Doyu , "grant.likely@linaro.org" CC: "thierry.reding@gmail.com" , "robherring2@gmail.com" , "joro@8bytes.org" , Stephen Warren , "will.deacon@arm.com" , "mark.rutland@arm.com" , "devicetree@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "linux-tegra@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "lorenzo.pieralisi@arm.com" , "galak@codeaurora.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCHv6+ 01/13] of: introduce of_property_for_earch_phandle_with_args() References: <1385041249-7705-1-git-send-email-hdoyu@nvidia.com><1385041249-7705-2-git-send-email-hdoyu@nvidia.com> <20131121.191720.1487772262083864095.hdoyu@nvidia.com> In-Reply-To: <20131121.191720.1487772262083864095.hdoyu@nvidia.com> X-Enigmail-Version: 1.5.2 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 On 11/21/2013 10:17 AM, Hiroshi Doyu wrote: > Iterating over a property containing a list of phandles with arguments > is a common operation for device drivers. This patch adds a new > of_property_for_each_phandle_with_args() macro to make the iteration > simpler. > > Signed-off-by: Hiroshi Doyu > --- > v6+: > Use the description, which Grant Likely proposed, to be full enough > that a future reader can figure out why a patch was written. > http://lists.linuxfoundation.org/pipermail/iommu/2013-November/007062.html This new version only addresses one of the concerns that Grant had, namely the commit message. > diff --git a/include/linux/of.h b/include/linux/of.h > +#define of_property_for_each_phandle_with_args(np, list, cells, i, args) \ > + for (i = 0; !of_parse_phandle_with_args(np, list, cells, i, args); i++) > + Grant also wanted the actual implementation fixed so that it wasn't so inefficient. What this current patch does is basically: for every entry in the property: for every entry in the property before the current index: parse the phandle+specifier That's roughly O(n^2). (n is # entries in the property) Instead, what should happen is: for every entry in the property: parse the phandle+specifier yield the result That's roughly O(n). In other words, an implementation more along the lines of include/linux/of.h's: #define of_property_for_each_u32(np, propname, prop, p, u) \ for (prop = of_find_property(np, propname, NULL), \ p = of_prop_next_u32(prop, NULL, &u); \ p; \ p = of_prop_next_u32(prop, p, &u)) ... so you'd need functions like of_prop_first_specifier() and of_prop_next_specifier(), and perhaps some associated set of state variables, perhaps with all the state wrapped into a single struct for simplicity.