From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailtransmit04.runbox.com (mailtransmit04.runbox.com [185.226.149.37]) (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 C4EC32F2603 for ; Mon, 8 Dec 2025 22:43:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.226.149.37 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765233812; cv=none; b=UR1xa4x2KZHlCbUQyNV32ipg3a/QsvpfaxJD5XMPLsDRmOioujvPW/pKEblTJwRWCvjRXc2EdA+b/9pW6YEX1Owa7IJT76Aoi+sW5ALse6UGkJLF+2I6Cewqn7VJnycF3SO/KBoMCictCug8bTj7URnQtcEnCZPXJP2q/ITwYLM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765233812; c=relaxed/simple; bh=fXGZ2M7xxYHgmTpQmtTDzEYbKvZXrYIjTdOkA45M/Q4=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=pLYpjVcHNE8AjJb8aMWo1Q+EkiO3mc4o6PMo+pYjKocLliT5JRuO8sCkz1UZZHYHNxUlP3CMgYSG9P+yvpJDRWuzQBXdqsjFGmzNkq1NV1LzJrt+kTFZcso0XM0tPsm7haeSHg6xAQwdoZ6wSMa7GEUKuPT+CBFH68xamFq8Wjo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=runbox.com; dkim=pass (2048-bit key) header.d=runbox.com header.i=@runbox.com header.b=lLzE9jSA; arc=none smtp.client-ip=185.226.149.37 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=runbox.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=runbox.com header.i=@runbox.com header.b="lLzE9jSA" Received: from mailtransmit02.runbox ([10.9.9.162] helo=aibo.runbox.com) by mailtransmit04.runbox.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1vSjx2-00F33D-Ln; Mon, 08 Dec 2025 23:43:28 +0100 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=runbox.com; s=selector2; h=Content-Transfer-Encoding:MIME-Version:References:In-Reply-To :Message-Id:Date:Subject:Cc:To:From; bh=pDzfAzksr2ZkqPsHEML95dRnTX61DmWnWyNEXtTl4FY=; b=lLzE9jSAe7v1sg+nYY9wWUTZz6 F3zBf94BxvGYhskX/Vit7iwvYDCW+4BKTsrSU7tcEd6rWjAJrh89oySdijqlLXOR0jfya4c0PDFD+ pMJK4NTIqHigTuzxFMhgLC36T3Qh+BSMvuMy7ChgZA/cP0SP2f1N/A1WkwrxzEeWGUCsxV7lfYgvq BX0jCejT92hqMy/8trQUQNkiJTUrEcxzZRng26WYrXDGD29s3Tcip+hLDLvXWHa2Wasku/EUeS1UG MZYeEtg0ku+qcUVnX+MIg6n1itJ/W8VIcIfCW5DW4Tz8RgCJuXQoDihtH3ZdrXLwZCzPKCNm2tGlY z9HnR00Q==; Received: from [10.9.9.74] (helo=submission03.runbox) by mailtransmit02.runbox with esmtp (Exim 4.86_2) (envelope-from ) id 1vSjx2-0003Ek-As; Mon, 08 Dec 2025 23:43:28 +0100 Received: by submission03.runbox with esmtpsa [Authenticated ID (1493616)] (TLS1.2:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.93) id 1vSjwj-00Ay0v-Tc; Mon, 08 Dec 2025 23:43:10 +0100 From: david.laight.linux@gmail.com To: Yury Norov , Rasmus Villemoes , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, Geert Uytterhoeven Cc: David Laight Subject: [PATCH 8/9] bitfield: Add comment block for the host/fixed endian functions Date: Mon, 8 Dec 2025 22:42:49 +0000 Message-Id: <20251208224250.536159-9-david.laight.linux@gmail.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20251208224250.536159-1-david.laight.linux@gmail.com> References: <20251208224250.536159-1-david.laight.linux@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: David Laight Copied almost verbatim from the commit message that added the functions. Signed-off-by: David Laight --- include/linux/bitfield.h | 43 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h index bfd80ebd25b1..9feb489a8da3 100644 --- a/include/linux/bitfield.h +++ b/include/linux/bitfield.h @@ -181,6 +181,49 @@ do { \ *_reg_p = (*_reg_p & ~_mask) | ((_val << __bf_shf(_mask)) & _mask); \ }) +/* + * Primitives for manipulating bitfields both in host- and fixed-endian. + * + * * u32 le32_get_bits(__le32 val, u32 field) extracts the contents of the + * bitfield specified by @field in little-endian 32bit object @val and + * converts it to host-endian. + * + * * void le32p_replace_bits(__le32 *p, u32 v, u32 field) replaces + * the contents of the bitfield specified by @field in little-endian + * 32bit object pointed to by @p with the value of @v. New value is + * given in host-endian and stored as little-endian. + * + * * __le32 le32_replace_bits(__le32 old, u32 v, u32 field) is equivalent to + * ({__le32 tmp = old; le32p_replace_bits(&tmp, v, field); tmp;}) + * In other words, instead of modifying an object in memory, it takes + * the initial value and returns the modified one. + * + * * __le32 le32_encode_bits(u32 v, u32 field) is equivalent to + * le32_replace_bits(0, v, field). In other words, it returns a little-endian + * 32bit object with the bitfield specified by @field containing the + * value of @v and all bits outside that bitfield being zero. + * + * Such set of helpers is defined for each of little-, big- and host-endian + * types; e.g. u64_get_bits(val, field) will return the contents of the bitfield + * specified by @field in host-endian 64bit object @val, etc. Of course, for + * host-endian no conversion is involved. + * + * Fields to access are specified as GENMASK() values - an N-bit field + * starting at bit #M is encoded as GENMASK(M + N - 1, M). Note that + * bit numbers refer to endianness of the object we are working with - + * e.g. GENMASK(11, 0) in __be16 refers to the second byte and the lower + * 4 bits of the first byte. In __le16 it would refer to the first byte + * and the lower 4 bits of the second byte, etc. + * + * Field specification must be a constant; __builtin_constant_p() doesn't + * have to be true for it, but compiler must be able to evaluate it at + * build time. If it cannot or if the value does not encode any bitfield, + * the build will fail. + * + * If the value being stored in a bitfield is a constant that does not fit + * into that bitfield, a warning will be generated at compile time. + */ + extern void __compiletime_error("value doesn't fit into mask") __field_overflow(void); extern void __compiletime_error("bad bitfield mask") -- 2.39.5