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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 392F2C282C6 for ; Mon, 3 Mar 2025 19:37:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=03jKLJv+9bUILeFzqqLHIJBVd5z/Dj9386BWFmbTxP0=; b=xGjzIqIJTCa5mb iUwmJabxXXsYOEJiM5mjB8peYh62mpD+LJI4FC9R64AjQG55LuCdB4gtkZE1dbTl4+GW9ydxcU+/A Aydc93TVeWpsLhupqgoZnLzG+7CfkeHWzg52b39AW5DqdyX71hd6a96Q7/sZSVWcdlTv2//SP3xjp q0hbiS4+yTLXg1jVLet4uEkIzyWNEYBYdAy1de01Zy4/qttG4+KBzmf23P1e15c1mg9efiWpWKwLf KRjO+1bNjXtfXxlQRiOxM7lksmaeS5zbOfm8wEe+aHSvYXfeCHu008pWeqe0GUDFl8c57q3hyh2j+ Jdl91iiX6hI0nzH20h3Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tpBbm-000000025EH-3gY8; Mon, 03 Mar 2025 19:37:46 +0000 Received: from mail-wm1-x335.google.com ([2a00:1450:4864:20::335]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tpBbk-000000025Da-0AyW for linux-mtd@lists.infradead.org; Mon, 03 Mar 2025 19:37:45 +0000 Received: by mail-wm1-x335.google.com with SMTP id 5b1f17b1804b1-439846bc7eeso31126925e9.3 for ; Mon, 03 Mar 2025 11:37:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1741030662; x=1741635462; darn=lists.infradead.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=LVBrsQeXraVCp2D/HwIHQkHOOS8UoeEI0fbbAugf/mo=; b=U6OeuJhtigOm4Yap4mQ0CnDiX2dDFuEot5OBjR/UzSW5bipHVFit0AZf58f8wLAYby /UsC1YHabFdZLdRmkzCM1slKEtSjX8Zk69RcApsg95WDhccoHT/Mh74r7DANt78vLgsB wgc39HjvpK+/8lBDpmsQlwcESml47BgZ+OQRYQ8VL6Wku5bynATaHD11b8/QK227nWHx cIQvMnkZYTC/NR6lAyXQ/m8jcAMLg9YSfNvNzx+HyCD0XwQA6MuxwnxcoOzAcS/eSddc enYLlLhcqRJBhuDwABb/iJ6yY+b8ReTAkloSSacoPqd1eucjiRy8BwgLQj+mdzoT93yu 9mWw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1741030662; x=1741635462; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=LVBrsQeXraVCp2D/HwIHQkHOOS8UoeEI0fbbAugf/mo=; b=AZc+C4ShNsYKQygzFvdCaAhw2Egrl4GtOxRz7TYcvqLoPwuyakvwESzHFuriuHw97c LrBClTu5tR4/nKJHtSPDPni9bXWGyYwubEBZf6eoYVzr6aPQ3TWbU+6AjFB9FoXwtZji 7w60RFBtuTDMIYHqEheCf4TlhgTm2lT4ZrZxRVIOmzhzKJYGP+UlSOc7/dCecf9QIP7d 6i5LfoPC6BEp2XtzQd+QANLU52wSR5qN4Lv0lLZ3y2yVxzv45ZLuvkAzfAkkmK6jbABN Q/w2PcfmnADYKwY5MFQIEVjx1EQF2qjo7vWErLvU9meRr0cE3RDDA1nc4QyF4hMG5kGD xB5Q== X-Forwarded-Encrypted: i=1; AJvYcCV5QoJ89xfbrK/EeVJwnVowaAuxhKO+ctdAwT8dpZJPNiLYJwI29jKNxPedq8Fp1d7poxpy9dnUG+8=@lists.infradead.org X-Gm-Message-State: AOJu0YyxnRpRrEqPj/KNxswdCQmKNS9tQmIJBChMDkUdUm/YWaPEGQ7P 9t5hYtYUSxckCMh6nuM2X/z0C3YytcyoxZmAuRIGUNI3McLqUIXn X-Gm-Gg: ASbGnctkcQxXXEgBNsSD07+UBTmYWTxor8vqyec9mB9fZe0r90E56X2wzzof6zBYdD8 ocgq0lwSKV+HcLnydzpF35Qg4KKczhqXf0nkS0Jq78Gy8ZW29voaAYJOC/ctKTpsryDvAyYk9E5 0H6Qpsfv8MWs2fePL9Vv3Rh8gPe5gQLNmq9jGCiGVAMfcpcngm1EHu2q4ofiNpPR3WodH4j08pq jRCF7KiygnUm4XEeIpoaOgOwgM8VSBFB/h7GSAoHRhsfVXsRP9fX+V++asvLswJOI18nF12MnnZ ZIOWOfFUtSppCnanovZLJxJjVc+gydnexmxY+vT5f8W6PCq5UA5BBE1iSqizhjl78+Ip20g69fF JfV5YhKM= X-Google-Smtp-Source: AGHT+IE5SsMAFxGhtu6mLXRY5Pge6T5PIIN9j46P3NC9S6x1AuYKxmDUwUSvWRO/DaRfnfW/d1a6Iw== X-Received: by 2002:a05:600c:1548:b0:439:685e:d4c8 with SMTP id 5b1f17b1804b1-43ba66fec18mr136187305e9.15.1741030662069; Mon, 03 Mar 2025 11:37:42 -0800 (PST) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-390e47b7a73sm15704508f8f.50.2025.03.03.11.37.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Mar 2025 11:37:41 -0800 (PST) Date: Mon, 3 Mar 2025 19:37:39 +0000 From: David Laight To: Yury Norov Cc: Kuan-Wei Chiu , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, jk@ozlabs.org, joel@jms.id.au, eajames@linux.ibm.com, andrzej.hajda@intel.com, neil.armstrong@linaro.org, rfoss@kernel.org, maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch, dmitry.torokhov@gmail.com, mchehab@kernel.org, awalls@md.metrocast.net, hverkuil@xs4all.nl, miquel.raynal@bootlin.com, richard@nod.at, vigneshr@ti.com, louis.peens@corigine.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, parthiban.veerasooran@microchip.com, arend.vanspriel@broadcom.com, johannes@sipsolutions.net, gregkh@linuxfoundation.org, jirislaby@kernel.org, akpm@linux-foundation.org, hpa@zytor.com, alistair@popple.id.au, linux@rasmusvillemoes.dk, Laurent.pinchart@ideasonboard.com, jonas@kwiboo.se, jernej.skrabec@gmail.com, kuba@kernel.org, linux-kernel@vger.kernel.org, linux-fsi@lists.ozlabs.org, dri-devel@lists.freedesktop.org, linux-input@vger.kernel.org, linux-media@vger.kernel.org, linux-mtd@lists.infradead.org, oss-drivers@corigine.com, netdev@vger.kernel.org, linux-wireless@vger.kernel.org, brcm80211@lists.linux.dev, brcm80211-dev-list.pdl@broadcom.com, linux-serial@vger.kernel.org, bpf@vger.kernel.org, jserv@ccns.ncku.edu.tw, andrew.cooper3@citrix.com, Yu-Chun Lin Subject: Re: [PATCH v2 01/18] lib/parity: Add __builtin_parity() fallback implementations Message-ID: <20250303193739.2a9cdc42@pumpkin> In-Reply-To: References: <20250301142409.2513835-1-visitorckw@gmail.com> <20250301142409.2513835-2-visitorckw@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250303_113744_091888_774B8EEF X-CRM114-Status: GOOD ( 60.62 ) X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org On Mon, 3 Mar 2025 10:15:41 -0500 Yury Norov wrote: > On Mon, Mar 03, 2025 at 01:29:19AM +0800, Kuan-Wei Chiu wrote: > > Hi Yury, > > > > On Sun, Mar 02, 2025 at 11:02:12AM -0500, Yury Norov wrote: > > > On Sun, Mar 02, 2025 at 04:20:02PM +0800, Kuan-Wei Chiu wrote: > > > > Hi Yury, > > > > > > > > On Sat, Mar 01, 2025 at 10:10:20PM -0500, Yury Norov wrote: > > > > > On Sat, Mar 01, 2025 at 10:23:52PM +0800, Kuan-Wei Chiu wrote: > > > > > > Add generic C implementations of __paritysi2(), __paritydi2(), and > > > > > > __parityti2() as fallback functions in lib/parity.c. These functions > > > > > > compute the parity of a given integer using a bitwise approach and are > > > > > > marked with __weak, allowing architecture-specific implementations to > > > > > > override them. > > > > > > > > > > > > This patch serves as preparation for using __builtin_parity() by > > > > > > ensuring a fallback mechanism is available when the compiler does not > > > > > > inline the __builtin_parity(). > > > > > > > > > > > > Co-developed-by: Yu-Chun Lin > > > > > > Signed-off-by: Yu-Chun Lin > > > > > > Signed-off-by: Kuan-Wei Chiu > > > > > > --- > > > > > > lib/Makefile | 2 +- > > > > > > lib/parity.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ > > > > > > 2 files changed, 49 insertions(+), 1 deletion(-) > > > > > > create mode 100644 lib/parity.c > > > > > > > > > > > > diff --git a/lib/Makefile b/lib/Makefile > > > > > > index 7bab71e59019..45affad85ee4 100644 > > > > > > --- a/lib/Makefile > > > > > > +++ b/lib/Makefile > > > > > > @@ -51,7 +51,7 @@ obj-y += bcd.o sort.o parser.o debug_locks.o random32.o \ > > > > > > bsearch.o find_bit.o llist.o lwq.o memweight.o kfifo.o \ > > > > > > percpu-refcount.o rhashtable.o base64.o \ > > > > > > once.o refcount.o rcuref.o usercopy.o errseq.o bucket_locks.o \ > > > > > > - generic-radix-tree.o bitmap-str.o > > > > > > + generic-radix-tree.o bitmap-str.o parity.o > > > > > > obj-y += string_helpers.o > > > > > > obj-y += hexdump.o > > > > > > obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o > > > > > > diff --git a/lib/parity.c b/lib/parity.c > > > > > > new file mode 100644 > > > > > > index 000000000000..a83ff8d96778 > > > > > > --- /dev/null > > > > > > +++ b/lib/parity.c > > > > > > @@ -0,0 +1,48 @@ > > > > > > +// SPDX-License-Identifier: GPL-2.0-only > > > > > > +/* > > > > > > + * lib/parity.c > > > > > > + * > > > > > > + * Copyright (C) 2025 Kuan-Wei Chiu > > > > > > + * Copyright (C) 2025 Yu-Chun Lin > > > > > > + * > > > > > > + * __parity[sdt]i2 can be overridden by linking arch-specific versions. > > > > > > + */ > > > > > > + > > > > > > +#include > > > > > > +#include > > > > > > + > > > > > > +/* > > > > > > + * One explanation of this algorithm: > > > > > > + * https://funloop.org/codex/problem/parity/README.html > > > > > > > > > > I already asked you not to spread this link. Is there any reason to > > > > > ignore it? > > > > > > > > > In v2, this algorithm was removed from bitops.h, so I moved the link > > > > here instead. I'm sorry if it seemed like I ignored your comment. > > > > > > Yes, it is. > > > > > > > In v1, I used the same approach as parity8() because I couldn't justify > > > > the performance impact in a specific driver or subsystem. However, > > > > multiple people commented on using __builtin_parity or an x86 assembly > > > > implementation. I'm not ignoring their feedback-I want to address these > > > > > > Please ask those multiple people: are they ready to maintain all that > > > zoo of macros, weak implementations, arch implementations and stubs > > > for no clear benefit? Performance is always worth it, but again I see > > > not even a hint that the drivers care about performance. You don't > > > measure it, so don't care as well. Right? > > > > > > > comments. Before submitting, I sent an email explaining my current > > > > approach: using David's suggested method along with __builtin_parity, > > > > but no one responded. So, I decided to submit v2 for discussion > > > > instead. > > > > > > For discussion use tag RFC. > > > > > > > > > > > To avoid mistakes in v3, I want to confirm the following changes before > > > > sending it: > > > > > > > > (a) Change the return type from int to bool. > > > > (b) Avoid __builtin_parity and use the same approach as parity8(). > > > > (c) Implement parity16/32/64() as single-line inline functions that > > > > call the next smaller variant after xor. > > > > (d) Add a parity() macro that selects the appropriate parityXX() based > > > > on type size. > > > > (e) Update users to use this parity() macro. > > > > > > > > However, (d) may require a patch affecting multiple subsystems at once > > > > since some places that already include bitops.h have functions named > > > > parity(), causing conflicts. Unless we decide not to add this macro in > > > > the end. > > > > > > > > As for checkpatch.pl warnings, they are mostly pre-existing coding > > > > style issues in this series. I've kept them as-is, but if preferred, > > > > I'm fine with fixing them. > > > > > > Checkpatch only complains on new lines. Particularly this patch should > > > trigger checkpatch warning because it adds a new file but doesn't touch > > > MAINTAINERS. > > > > > For example, the following warning: > > > > ERROR: space required after that ',' (ctx:VxV) > > #84: FILE: drivers/input/joystick/sidewinder.c:368: > > + if (!parity64(GB(0,33))) > > ^ > > > > This issue already existed before this series, and I'm keeping its > > style unchanged for now. > > > > > > If anything is incorrect or if there are concerns, please let me know. > > > > > > > > Regards, > > > > Kuan-Wei > > > > > > > > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > > > > index c1cb53cf2f0f..47b7eca8d3b7 100644 > > > > --- a/include/linux/bitops.h > > > > +++ b/include/linux/bitops.h > > > > @@ -260,6 +260,43 @@ static inline int parity8(u8 val) > > > > return (0x6996 >> (val & 0xf)) & 1; > > > > } > > > > > > > > +static inline bool parity16(u16 val) > > > > +{ > > > > + return parity8(val ^ (val >> 8)); > > > > +} > > > > + > > > > +static inline bool parity32(u32 val) > > > > +{ > > > > + return parity16(val ^ (val >> 16)); > > > > +} > > > > + > > > > +static inline bool parity64(u64 val) > > > > +{ > > > > + return parity32(val ^ (val >> 32)); > > > > +} > > > > > > That was discussed between Jiri and me in v2. Fixed types functions > > > are needed only in a few very specific cases. With the exception of > > > I3C driver (which doesn't look good for both Jiri and me), all the > > > drivers have the type of variable passed to the parityXX() matching > > > the actual variable length. It means that fixed-type versions of the > > > parity() are simply not needed. So if we don't need them, please don't > > > introduce it. > > > > > So, I should add the following parity() macro in v3, remove parity8(), > > and update all current parity8() users to use this macro, right? > > If you go with macro, please apply my patch and modify it in-place > with this __auto_type thing and GCC hack. Feel free to add your > co-developed-by, or tested, or whatever. > > > I changed u64 to __auto_type and applied David's suggestion to replace > > the >> 32 with >> 16 >> 16 to avoid compiler warnings. > > > > Regards, > > Kuan-Wei > > > > #define parity(val) \ > > ({ \ > > __auto_type __v = (val); \ > > bool __ret; \ > > switch (BITS_PER_TYPE(val)) { \ > > case 64: \ > > __v ^= __v >> 16 >> 16; \ > > fallthrough; \ > > This hack should be GCC-only, and well documented. > For clang it should be > __v ^= __v >> 32; \ There is no point doing a conditional - it just obscures things. > > > case 32: \ > > __v ^= __v >> 16; \ > > fallthrough; \ > > case 16: \ > > __v ^= __v >> 8; \ > > fallthrough; \ > > case 8: \ > > __v ^= __v >> 4; \ > > __ret = (0x6996 >> (__v & 0xf)) & 1; \ > > break; \ > > default: \ > > BUILD_BUG(); \ > > } \ > > __ret; \ > > }) ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/