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 B1F6CC282CD for ; Mon, 3 Mar 2025 15:17:45 +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:In-Reply-To:MIME-Version:References: 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=a+y8pTu4TwvraDF+LHLYl+yM7/Bii0YBlhsF7jdfbN0=; b=Y5asYpgS4R+Fxf 5PKp580MxUfuzjfyOO0LfeCKHfMmZwMYyB8xozl/GCuaBZvcCNoA8++qGu+vDweskchBtVGDktNTS HFsRV9BnmMGfZNj852kRjnbrs9T9g4WHhEv3pj9F+BjrQJ+sWVIqKngc35p2CPFHXkYRsF6RV5Qgi foVzJG5TIGcGwudw5Qv4gHSw0L9E7RgLItmS2FbKwetEH4/UWWkU10BFoJnwmQGTY8thMgxRWUJuC bEfX3+o7WfNpKnQaIfrD4mpYdiOGuOREM5KZMgNjlvdqcfVt1ckeagthzL6rqdmnJSZcl5eOIA9m9 CUZO8KKvV02cd43P21Qg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tp7Y3-00000001GVG-39Oe; Mon, 03 Mar 2025 15:17:39 +0000 Received: from mail-yw1-x1135.google.com ([2607:f8b0:4864:20::1135]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tp7WD-00000001FuK-3Hzg for linux-mtd@lists.infradead.org; Mon, 03 Mar 2025 15:15:47 +0000 Received: by mail-yw1-x1135.google.com with SMTP id 00721157ae682-6ef9b8b4f13so38513467b3.2 for ; Mon, 03 Mar 2025 07:15:44 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1741014943; x=1741619743; darn=lists.infradead.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=vnZYfHRjSrDXnbFHbwXoqUV2Rvz3Z3oSLKKN3IWdcq0=; b=HBhqWR8f3YnsVSj0qZGv0gfZl0Omji8lVv1GJMhg24Xo0/qXdMJc/q+iZttp+wc+Ep FSLhROqUtcJCUukYzSnaWCGWjbApcNCWCKannXSk8/87XIFPF1DfHgvVTmJjwToLV6il LHJuPn8+zPDLBJH8AsFXPZfcpSwQ5JWYEvIxRI2kZRuHaubNbU/aoGyY40d6PVzgWwa5 gAkr1ciOyN+18PLo59tlwYUQb7fnEKAEghTK5p280DDKhBn3LwKafmINu5VEzFsmjdHS yzOsRhNpyTe1UH+pIuTE1aYCfAUztfzvKgKL8GHnLJAw4B5atahWoozZAhGYpnibDIaX ka9A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1741014943; x=1741619743; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=vnZYfHRjSrDXnbFHbwXoqUV2Rvz3Z3oSLKKN3IWdcq0=; b=o4bFsXWx6sM7agyxOECT82NUbi1VRCWM1ojx2FdZfk8L4LGVsRr9lYgHuDYJ4eLFUZ R2lbD+ECrdjLuYmGzJfDh2otOSbPRUk9m8H8E6GkIHGqnSATMEYSc4pkk9YmL1PkkZl2 EirLWcuaW3ipMnK3Rke4fdtwDQ11oTOIcAcalbau6UHi1qajHyD7VJzh3Uq/mtC/eAQx bq/FpNE8U13nkxRnNwmgy4lMXu3l0E04A4P8hWYe2GutHm5r4PmJniy3MVsbMCirH+6z eWi/eYo+oh91Rn1uXyXp/jnXMItcfXdbJLcqArbdiwkuL2Sg73B54t3yXSrIJOx5W7k8 wQjw== X-Forwarded-Encrypted: i=1; AJvYcCVapkzSYOnbGVnrChSSlx3ZQ3OF3DEnzVSTbUvq+04d+aDDOoNH3Y/UHAXoYX54m8f/OL/m2/WW9Pg=@lists.infradead.org X-Gm-Message-State: AOJu0YwwCSofFK3fTHZvzEBOKD+Hdc0jzQoj+CPseMyCge+7OH84asAc Owo48ltogA0q04R3KgrOffKX9OXuos5WAEs/tOPUud8ozT6PWhrt X-Gm-Gg: ASbGnctktLA0CHlZTv3owhJpljtcFQwPEEGQh2rpnZTIoyJJTFLKprBN1VNUqa5EMLo TShGGZlE0j+XLDSCCdHI/eYFcY1NM3v/6U5hUoEDv8NzP0eHAGzoiH+xF/qSHl7ZtNOVN42ysVE ziQFXPpfc4q2FkP3iNUEqQZBdW/0FaqjrMja/IY9EbFht/i1ffGHg3zug2DQgxj44sgaGBIdKOJ dSp67P/b9liMO3m+CnEh88QCJTq853eKfO+e+MMhuWiHXr/RDEi4Sq3SzGoeHSaGLZukzxv+WKp O6OZltnbzmP28xPILxDECtTPL77pmlFlb16rMusIKIYoua4QTjLC8gH4qm+7TTDhzchc/r0rxKL 7bM2q X-Google-Smtp-Source: AGHT+IEY4hJ4+y0MnSwcin/X5yMbfMX2rlPGrxXj2stWp9C4NMGoZplIcoPGEYKHHfJxM+PTRJ4GqA== X-Received: by 2002:a05:690c:3686:b0:6f9:ad48:a3c7 with SMTP id 00721157ae682-6fd4a0acc71mr190341807b3.21.1741014942895; Mon, 03 Mar 2025 07:15:42 -0800 (PST) Received: from localhost (c-73-224-175-84.hsd1.fl.comcast.net. [73.224.175.84]) by smtp.gmail.com with ESMTPSA id 00721157ae682-6fd6b9619c5sm9708167b3.75.2025.03.03.07.15.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Mar 2025 07:15:42 -0800 (PST) Date: Mon, 3 Mar 2025 10:15:41 -0500 From: Yury Norov To: Kuan-Wei Chiu Cc: 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, david.laight.linux@gmail.com, andrew.cooper3@citrix.com, Yu-Chun Lin Subject: Re: [PATCH v2 01/18] lib/parity: Add __builtin_parity() fallback implementations Message-ID: References: <20250301142409.2513835-1-visitorckw@gmail.com> <20250301142409.2513835-2-visitorckw@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250303_071545_847170_F97248AF X-CRM114-Status: GOOD ( 57.04 ) 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, 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; \ > 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/