From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCHv6+ 01/13] of: introduce of_property_for_earch_phandle_with_args() Date: Thu, 21 Nov 2013 11:57:00 -0700 Message-ID: <528E577C.2050506@wwwdotorg.org> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20131121.191720.1487772262083864095.hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Hiroshi Doyu , "grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org" Cc: "mark.rutland-5wv7dgnIgG8@public.gmane.org" , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "lorenzo.pieralisi-5wv7dgnIgG8@public.gmane.org" , Stephen Warren , "will.deacon-5wv7dgnIgG8@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org" , "robherring2-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org" , "galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org" , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" List-Id: linux-tegra@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.