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=-2.2 required=3.0 tests=DKIM_ADSP_CUSTOM_MED, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 04F5CECE58E for ; Thu, 10 Oct 2019 08:08:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA20820B7C for ; Thu, 10 Oct 2019 08:08:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733138AbfJJIH7 (ORCPT ); Thu, 10 Oct 2019 04:07:59 -0400 Received: from mga04.intel.com ([192.55.52.120]:43656 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733089AbfJJIH7 (ORCPT ); Thu, 10 Oct 2019 04:07:59 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Oct 2019 01:07:58 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.67,279,1566889200"; d="scan'208";a="197171942" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by orsmga003.jf.intel.com with ESMTP; 10 Oct 2019 01:07:53 -0700 Received: from andy by smile with local (Exim 4.92.2) (envelope-from ) id 1iITUE-0002L7-QG; Thu, 10 Oct 2019 11:07:50 +0300 Date: Thu, 10 Oct 2019 11:07:50 +0300 From: Andy Shevchenko To: Geert Uytterhoeven Cc: Masahiro Yamada , William Breathitt Gray , Linus Walleij , Bartosz Golaszewski , Andrew Morton , "open list:GPIO SUBSYSTEM" , Linux Kernel Mailing List , linux-arch , Rasmus Villemoes , linux-arm-kernel , Linux PM mailing list , Phil Reid , Lukas Wunner , sean.nyekjaer@prevas.dk, morten.tiljeset@prevas.dk, Arnd Bergmann Subject: Re: [PATCH v17 01/14] bitops: Introduce the for_each_set_clump8 macro Message-ID: <20191010080750.GN32742@smile.fi.intel.com> References: <893c3b4f03266c9496137cc98ac2b1bd27f92c73.1570633189.git.vilhelm.gray@gmail.com> <20191009170917.GG32742@smile.fi.intel.com> 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 User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 10, 2019 at 09:49:51AM +0200, Geert Uytterhoeven wrote: > On Thu, Oct 10, 2019 at 9:42 AM Andy Shevchenko > wrote: > > On Thu, Oct 10, 2019 at 9:29 AM Geert Uytterhoeven wrote: > > > On Thu, Oct 10, 2019 at 7:49 AM Andy Shevchenko > > > wrote: > > > > On Thu, Oct 10, 2019 at 5:31 AM Masahiro Yamada > > > > wrote: > > > > > On Thu, Oct 10, 2019 at 3:54 AM Geert Uytterhoeven wrote: > > > > > > On Wed, Oct 9, 2019 at 7:09 PM Andy Shevchenko > > > > > > wrote: > > > > > > > On Thu, Oct 10, 2019 at 01:28:08AM +0900, Masahiro Yamada wrote: > > > > > > > > On Thu, Oct 10, 2019 at 12:27 AM William Breathitt Gray > > > > > > > > wrote: > > > > > > > > Why is the return type "unsigned long" where you know > > > > > > > > it return the 8-bit value ? > > > > > > > > > > > > > > Because bitmap API operates on unsigned long type. This is not only > > > > > > > consistency, but for sake of flexibility in case we would like to introduce > > > > > > > more calls like clump16 or so. > > > > > > > > > > > > TBH, that doesn't convince me: those functions explicitly take/return an > > > > > > 8-bit value, and have "8" in their name. The 8-bit value is never > > > > > > really related to, retrieved from, or stored in a full "unsigned long" > > > > > > element of a bitmap, only to/from/in a part (byte) of it. > > > > > > > > > > > > Following your rationale, all of iowrite{8,16,32,64}*() should take an > > > > > > "unsigned long" value, too. > > > > > > > > > > Using u8/u16/u32/u64 looks more consistent with other bitmap helpers. > > > > > > > > > > void bitmap_from_arr32(unsigned long *bitmap, const u32 *buf, unsigned > > > > > int nbits); > > > > > void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits); > > > > > static inline void bitmap_from_u64(unsigned long *dst, u64 mask); > > > > > > > > > > If you want to see more examples from other parts, > > > > > > > > Geert's and yours examples both are not related. They are about > > > > fixed-width properies when we know that is the part of protocol. > > > > Here we have no protocol which stricts us to the mentioned fixed-width types. > > > > > > Yes you have: they are functions to store/retrieve an 8-bit value from > > > the middle of the bitmap, which is reflected in their names ("clump8", > > > "value8"). > > > The input/output value is clearly separated from the actual bitmap, > > > which is referenced by the "unsigned long *". > > > > > > If you add new "value16" functions, they will be intended to store/retrieve > > > 16-bit values. > > > > And if I add 4-bit, 12-bit or 24-bit values, what should I use? > > Whatever is needed to store that? > I agree "unsigned long" is appropriate for a generic function to extract a > bit field of 1 to BITS_PER_LONG bits. > > > > Besides, if retrieving an 8-bit value requires passing an > > > "unsigned long *", the caller needs two variables: one unsigned long to > > > pass the address of, and one u8 to copy the returned value into. > > > > Why do you need a temporary variable? In some cases it might make > > sense, but in general simple cases I don't see what you may achieve > > with it. > > Because find_next_clump8() takes a pointer to store the output value. So does regmap_read(). 8 appeared there during review when it has been proposed to optimize to 8-bit clumps as most of the current users utilize it. The initial idea was to be bit-width agnostic. And with current API it's possible to easy convert to other formats later if we need. > > I looked at bitmap.h and see few functions may have benefited of > > actually eliminating a use of long -> u8 -> long conversion. > > > > Here is the question what we are mostly doing after we got a clump out > > of bitmap. > > If I call find_next_clump8() to extract a byte, I guess I want to process an u8 > aftwerwards? Some functions may expect a width-(semi-)dependent types, like regmap_write(). Yes, it's possible to supply u8 there and have an implicit type cast. -- With Best Regards, Andy Shevchenko