From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CB0F2C47247 for ; Mon, 4 May 2020 11:41:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B122524956 for ; Mon, 4 May 2020 11:41:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728614AbgEDLlM (ORCPT ); Mon, 4 May 2020 07:41:12 -0400 Received: from mga18.intel.com ([134.134.136.126]:57390 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726797AbgEDLlL (ORCPT ); Mon, 4 May 2020 07:41:11 -0400 IronPort-SDR: SQuyBrnTNt/XjkAq/e7HnsbwGtIBWgOWFBKaSarp61eXXnHU9GKjwB9Atffxlgh+N/xT8lVnIR Dq4P9W+1LzXA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 May 2020 04:41:10 -0700 IronPort-SDR: nK1XVmEP/7h0Dz9nRq3BHsCwEWqIAqIaOYKzPSsL9UGWuseFvAxw0CBmTaJZwhBHb/MKLwbX/x FvpEWpGlLdfg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,351,1583222400"; d="scan'208";a="248193832" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by orsmga007.jf.intel.com with ESMTP; 04 May 2020 04:41:06 -0700 Received: from andy by smile with local (Exim 4.93) (envelope-from ) id 1jVZTB-004bjy-4p; Mon, 04 May 2020 14:41:09 +0300 Date: Mon, 4 May 2020 14:41:09 +0300 From: Andy Shevchenko To: Syed Nayyar Waris Cc: akpm@linux-foundation.org, vilhelm.gray@gmail.com, michal.simek@xilinx.com, arnd@arndb.de, rrichter@marvell.com, linus.walleij@linaro.org, bgolaszewski@baylibre.com, yamada.masahiro@socionext.com, rui.zhang@intel.com, daniel.lezcano@linaro.org, amit.kucheria@verdurent.com, linux-arch@vger.kernel.org, linux-gpio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org Subject: Re: [PATCH v5 0/4] Introduce the for_each_set_clump macro Message-ID: <20200504114109.GE185537@smile.fi.intel.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, May 03, 2020 at 04:38:36AM +0530, Syed Nayyar Waris wrote: > This patchset introduces a new generic version of for_each_set_clump. > The previous version of for_each_set_clump8 used a fixed size 8-bit > clump, but the new generic version can work with clump of any size but > less than or equal to BITS_PER_LONG. The patchset utilizes the new macro > in several GPIO drivers. > > The earlier 8-bit for_each_set_clump8 facilitated a > for-loop syntax that iterates over a memory region entire groups of set > bits at a time. > > For example, suppose you would like to iterate over a 32-bit integer 8 > bits at a time, skipping over 8-bit groups with no set bit, where > XXXXXXXX represents the current 8-bit group: > > Example: 10111110 00000000 11111111 00110011 > First loop: 10111110 00000000 11111111 XXXXXXXX > Second loop: 10111110 00000000 XXXXXXXX 00110011 > Third loop: XXXXXXXX 00000000 11111111 00110011 > > Each iteration of the loop returns the next 8-bit group that has at > least one set bit. > > But with the new for_each_set_clump the clump size can be different from 8 bits. > Moreover, the clump can be split at word boundary in situations where word > size is not multiple of clump size. Following are examples showing the working > of new macro for clump sizes of 24 bits and 6 bits. > > Example 1: > clump size: 24 bits, Number of clumps (or ports): 10 > bitmap stores the bit information from where successive clumps are retrieved. > > /* bitmap memory region */ > 0x00aa0000ff000000; /* Most significant bits */ > 0xaaaaaa0000ff0000; > 0x000000aa000000aa; > 0xbbbbabcdeffedcba; /* Least significant bits */ > > Different iterations of for_each_set_clump:- > 'offset' is the bit position and 'clump' is the 24 bit clump from the > above bitmap. > Iteration first: offset: 0 clump: 0xfedcba > Iteration second: offset: 24 clump: 0xabcdef > Iteration third: offset: 48 clump: 0xaabbbb > Iteration fourth: offset: 96 clump: 0xaa > Iteration fifth: offset: 144 clump: 0xff > Iteration sixth: offset: 168 clump: 0xaaaaaa > Iteration seventh: offset: 216 clump: 0xff > Loop breaks because in the end the remaining bits (0x00aa) size was less > than clump size of 24 bits. > > In above example it can be seen that in iteration third, the 24 bit clump > that was retrieved was split between bitmap[0] and bitmap[1]. This example > also shows that 24 bit zeroes if present in between, were skipped (preserving > the previous for_each_set_macro8 behaviour). > > Example 2: > clump size = 6 bits, Number of clumps (or ports) = 3. > > /* bitmap memory region */ > 0x00aa0000ff000000; /* Most significant bits */ > 0xaaaaaa0000ff0000; > 0x0f00000000000000; > 0x0000000000000ac0; /* Least significant bits */ > > Different iterations of for_each_set_clump: > 'offset' is the bit position and 'clump' is the 6 bit clump from the > above bitmap. > Iteration first: offset: 6 clump: 0x2b > Loop breaks because 6 * 3 = 18 bits traversed in bitmap. > Here 6 * 3 is clump size * no. of clumps. Looking into the last patches where we have examples I still do not see a benefit of variadic clump sizes. power of 2 sizes would make sense (and be optimized accordingly (64-bit, 32-bit). -- With Best Regards, Andy Shevchenko