From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout02.his.huawei.com (canpmsgout02.his.huawei.com [113.46.200.217]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 683BD26B2D3; Tue, 9 Jun 2026 01:53:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.217 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780970025; cv=none; b=o6KOvNzo75JlXAnUqykSUdi3wfWpDfA9sYk4+YhBNstYyUseNEJf7afGmCAwDyBSSCE7QKlgCM6bHbaal/3+CsPfq3xbMe69DYLSQ4CzIBnQ3EvXaCZc5Mc0v1Q7L2tC0COEd6SdJmv8bz/qKNlSC6T2U44li5+Sg2He2BLox00= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780970025; c=relaxed/simple; bh=1YR1TlFy8rdpDyUa01leLBgZiwvXHIjqEhqXwyvuYL4=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=p9RAarX3DGD1aSDCZ32oVr14qKv2WKw7zQQmmUEnOZU2/aErppnpgXiu4bvuL3VqjUJTobnFI1JN/nkX63Bqt5svXVtd+UAWENVy1k+qyUDc8UokXzit+4Vv+AV2cHTzl49jaFBbzEiEGVkF0Q0un8YaVKXDRUKLd3AB42FcC8o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=ef/MIZuX; arc=none smtp.client-ip=113.46.200.217 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="ef/MIZuX" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=mka3w3BI1l7jdb6CzO1A3gkyAdvjTIHuJhEcsHosDQU=; b=ef/MIZuXfPFSnQJxprUwGgoFDlM9Q39furpMEEbHtDw5Ed5jedLc4ab+G0UzS5U78IeAv6Io5 kDWKLLy79eMr5d9b/uTMyScsJqIzQIss5/KqJPxBBaHKEML39BRunvvDZWzxQXIBT4LbHBGzl3R pkGyhihP7ggRTd3+ir7S0Z0= Received: from mail.maildlp.com (unknown [172.19.162.197]) by canpmsgout02.his.huawei.com (SkyGuard) with ESMTPS id 4gZBZ103V5zcZyh; Tue, 9 Jun 2026 09:45:29 +0800 (CST) Received: from dggpemf500011.china.huawei.com (unknown [7.185.36.131]) by mail.maildlp.com (Postfix) with ESMTPS id 8E32040576; Tue, 9 Jun 2026 09:53:38 +0800 (CST) Received: from [10.67.109.254] (10.67.109.254) by dggpemf500011.china.huawei.com (7.185.36.131) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 9 Jun 2026 09:53:36 +0800 Message-ID: <81d1ae23-8d18-4dff-a5c9-1824980b08ef@huawei.com> Date: Tue, 9 Jun 2026 09:53:36 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/5] lib/bitrev: Introduce GENERIC_BITREVERSE To: Yury Norov , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Yury Norov , Rasmus Villemoes , Arnd Bergmann , Eric Biggers , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Andrew Morton , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , , , , , References: <20260506175207.110893-1-ynorov@nvidia.com> <20260506175207.110893-3-ynorov@nvidia.com> From: Jinjie Ruan In-Reply-To: <20260506175207.110893-3-ynorov@nvidia.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: kwepems200002.china.huawei.com (7.221.188.68) To dggpemf500011.china.huawei.com (7.185.36.131) On 5/7/2026 1:52 AM, Yury Norov wrote: > The generic bit reversal implementation is controlled by > !HAVE_ARCH_BITREVERSE. This makes it difficult for architectures to > provide a hardware-accelerated implementation while being able to > fall back to the generic version if needed. > > This patch adds GENERIC_BITREVERSE, so bitreverse API is controlled by > BITREVERSE, GENERIC_BITREVERSE and HAVE_ARCH_BITREVERSE options. The > relationship between them is described as follows: > > - BITREVERSE is selected by user code; it's required to generate the API; > - Architectures may select HAVE_ARCH_BITREVERSE and provide an arch > implementation in arch/$(ARCH)/include/asm/bitrev.h. > - if HAVE_ARCH_BITREVERSE isn't set, BITREVERSE selects GENERIC_BITREVERSE; > - if GENERIC_BITREVERSE is set and HAVE_ARCH_BITREVERSE is not, the kernel > provides generic implementation only, and wires bitrevXX() to it. > - if HAVE_ARCH_BITREVERSE is set and GENERIC_BITREVERSE is not, the arch > code provides __arch_bitrevXX(), and it is wired to bitrevXX(); > - if both GENERIC_BITREVERSE and HAVE_ARCH_BITREVERSE are selected, the kernel > generates generic___bitrev(), but wires bitrev() to the __arch_bitrev(). > > The last option allows architectures to use generic___bitrev() as a > fallback option. > > Drivers and core code should never select GENERIC_BITREVERSE or > HAVE_ARCH_BITREVERSE explicitly. > > Architectures that require generic bitreverse API as a fallback should > explicitly enable GENERIC_BITREVERSE together with HAVE_ARCH_BITREVERSE. > > Signed-off-by: Yury Norov > --- > lib/Kconfig | 12 ++++++++++++ > lib/Makefile | 2 +- > lib/bitrev.c | 3 --- > 3 files changed, 13 insertions(+), 4 deletions(-) > > diff --git a/lib/Kconfig b/lib/Kconfig > index d8e7e89ae320..a33988adfaa3 100644 > --- a/lib/Kconfig > +++ b/lib/Kconfig > @@ -54,6 +54,7 @@ config PACKING_KUNIT_TEST > > config BITREVERSE > tristate > + select GENERIC_BITREVERSE if !HAVE_ARCH_BITREVERSE > > config HAVE_ARCH_BITREVERSE > bool > @@ -63,6 +64,17 @@ config HAVE_ARCH_BITREVERSE > This option enables the use of hardware bit-reversal instructions on > architectures which support such operations. > > +config GENERIC_BITREVERSE > + tristate > + depends on BITREVERSE > + help > + Generic bit reversal implementation. Drivers should never enable > + it explicitly. Instead, enable BITREVERSE. The later riscv implementation force GENERIC_BITREVERSE even when HAVE_ARCH_BITREVERSE=y but triggers a Kconfig unmet direct dependency warning as below: warning: (RISCV) selects GENERIC_BITREVERSE which has unmet direct dependencies (BITREVERSE) This happens because select ignores depends on clauses and can force a tristate symbol to y even when its dependency BITREVERSE is only =m. The warning is a symptom of an invalid dependency chain. Link: https://lore.kernel.org/all/20260506214943.1AAE8C2BCB0@smtp.kernel.org/ > + > + Architectures may want to select it as a fall-back option for > + HAVE_ARCH_BITREVERSE, when the hardware-accelerated bit reverse > + instruction set is optional, like RISC-V ZBKB extension. > + > config ARCH_HAS_STRNCPY_FROM_USER > bool > > diff --git a/lib/Makefile b/lib/Makefile > index f33a24bf1c19..23e07d19d01c 100644 > --- a/lib/Makefile > +++ b/lib/Makefile > @@ -145,7 +145,7 @@ obj-$(CONFIG_DEBUG_PREEMPT) += smp_processor_id.o > obj-$(CONFIG_LIST_HARDENED) += list_debug.o > obj-$(CONFIG_DEBUG_OBJECTS) += debugobjects.o > > -obj-$(CONFIG_BITREVERSE) += bitrev.o > +obj-$(CONFIG_GENERIC_BITREVERSE) += bitrev.o > obj-$(CONFIG_LINEAR_RANGES) += linear_ranges.o > obj-$(CONFIG_PACKING) += packing.o > obj-$(CONFIG_PACKING_KUNIT_TEST) += packing_test.o > diff --git a/lib/bitrev.c b/lib/bitrev.c > index 81b56e0a7f32..05088231f31f 100644 > --- a/lib/bitrev.c > +++ b/lib/bitrev.c > @@ -1,5 +1,4 @@ > // SPDX-License-Identifier: GPL-2.0-only > -#ifndef CONFIG_HAVE_ARCH_BITREVERSE > #include > #include > #include > @@ -43,5 +42,3 @@ const u8 byte_rev_table[256] = { > 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff, > }; > EXPORT_SYMBOL_GPL(byte_rev_table); > - > -#endif /* CONFIG_HAVE_ARCH_BITREVERSE */