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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Andrew Morton , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Jinjie Ruan , linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Cc: Yury Norov Subject: [PATCH v2 2/5] lib/bitrev: Introduce GENERIC_BITREVERSE Date: Wed, 6 May 2026 13:52:03 -0400 Message-ID: <20260506175207.110893-3-ynorov@nvidia.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260506175207.110893-1-ynorov@nvidia.com> References: <20260506175207.110893-1-ynorov@nvidia.com> X-ClientProxiedBy: BY1P220CA0002.NAMP220.PROD.OUTLOOK.COM (2603:10b6:a03:59d::6) To CY8PR12MB8300.namprd12.prod.outlook.com (2603:10b6:930:7d::16) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CY8PR12MB8300:EE_|CH3PR12MB8188:EE_ X-MS-Office365-Filtering-Correlation-Id: 636bcd07-d154-4d9d-753b-08deab983597 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|10070799003|7416014|376014|1800799024|921020|3023799003|18002099003|56012099003|22082099003; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org 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. + + 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 */ -- 2.51.0 _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv