Return-path: Received: from mail-wm0-f46.google.com ([74.125.82.46]:36544 "EHLO mail-wm0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753806AbcHSD7V (ORCPT ); Thu, 18 Aug 2016 23:59:21 -0400 Received: by mail-wm0-f46.google.com with SMTP id q128so18843393wma.1 for ; Thu, 18 Aug 2016 20:58:54 -0700 (PDT) From: Jakub Kicinski To: torvalds@linux-foundation.org Cc: akpm@linux-foundation.org, gregkh@linuxfoundation.org, davem@davemloft.net, kvalo@codeaurora.org, linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org, dinan.gunawardena@netronome.com, Jakub Kicinski Subject: [RFC (v7)] add basic register-field manipulation macros Date: Thu, 18 Aug 2016 18:11:57 +0100 Message-Id: <1471540317-14823-1-git-send-email-jakub.kicinski@netronome.com> (sfid-20160819_055927_563707_B50A27EC) In-Reply-To: References: Sender: linux-wireless-owner@vger.kernel.org List-ID: Hi! This is what I came up with. Changes: - drop the explicit type marking (u32/u64) - depend on the type of the mask instead; - only allow compilation time constant masks; - barf at "type of register too small to ever match mask" on get; - rename PUT -> PREP. I did not put the new marcos in bitops.h (where GENMASK lives) because of the dependency on bug.h. If I did there would be a circular dependency like this: bitops.h -> linux/bug.h -> asm-generic/bug.h -> kernel.h -> bitops.h Which makes things really ugly. I tried to remove the kernel.h include from bug.h by separating panic-related definitions into a new header. There were still cycles coming from the notifier.h which I had to include for panic notifier... Reviewed-by: Dinan Gunawardena Signed-off-by: Jakub Kicinski --- include/linux/bitfield.h | 93 ++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/bug.h | 3 ++ 2 files changed, 96 insertions(+) create mode 100644 include/linux/bitfield.h diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h new file mode 100644 index 000000000000..32ca8863e66d --- /dev/null +++ b/include/linux/bitfield.h @@ -0,0 +1,93 @@ +/* + * Copyright (C) 2014 Felix Fietkau + * Copyright (C) 2004 - 2009 Ivo van Doorn + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + */ + +#ifndef _LINUX_BITFIELD_H +#define _LINUX_BITFIELD_H + +#include + +/* + * Bitfield access macros + * + * FIELD_{GET,PREP} macros take as first parameter shifted mask + * from which they extract the base mask and shift amount. + * Mask must be a compilation time constant. + * + * Example: + * + * #define REG_FIELD_A GENMASK(6, 0) + * #define REG_FIELD_B BIT(7) + * #define REG_FIELD_C GENMASK(15, 8) + * #define REG_FIELD_D GENMASK(31, 16) + * + * Get: + * a = FIELD_GET(REG_FIELD_A, reg); + * b = FIELD_GET(REG_FIELD_B, reg); + * + * Set: + * reg = FIELD_PREP(REG_FIELD_A, 1) | + * FIELD_PREP(REG_FIELD_B, 0) | + * FIELD_PREP(REG_FIELD_C, c) | + * FIELD_PREP(REG_FIELD_D, 0x40); + * + * Modify: + * reg &= ~REG_FIELD_C; + * reg |= FIELD_PREP(REG_FIELD_C, c); + */ + +#define _bf_shf(x) (__builtin_ffsll(x) - 1) + +#define _BF_FIELD_CHECK(_mask, _reg, _val, _pfx) \ + ({ \ + BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), \ + _pfx "mask is not constant"); \ + BUILD_BUG_ON_MSG(!(_mask), _pfx "mask is zero"); \ + BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ? \ + ~((_mask) >> _bf_shf(_mask)) & (_val) : 0, \ + _pfx "value too large for the field"); \ + BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull, \ + _pfx "type of reg too small for mask"); \ + __BUILD_BUG_ON_NOT_POWER_OF_2((_mask) + \ + (1ULL << _bf_shf(_mask))); \ + }) + +/** + * FIELD_PREP() - prepare a bitfield element + * @_mask: shifted mask defining the field's length and position + * @_val: value to put in the field + * + * FIELD_PREP() masks and shifts up the value. The result should + * be combined with other fields of the bitfield using logical OR. + */ +#define FIELD_PREP(_mask, _val) \ + ({ \ + _BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \ + ((typeof(_mask))(_val) << _bf_shf(_mask)) & (_mask); \ + }) + +/** + * FIELD_GET() - extract a bitfield element + * @_mask: shifted mask defining the field's length and position + * @_reg: 32bit value of entire bitfield + * + * FIELD_GET() extracts the field specified by @_mask from the + * bitfield passed in as @_reg by masking and shifting it down. + */ +#define FIELD_GET(_mask, _reg) \ + ({ \ + _BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: "); \ + (typeof(_mask))(((_reg) & (_mask)) >> _bf_shf(_mask)); \ + }) + +#endif diff --git a/include/linux/bug.h b/include/linux/bug.h index e51b0709e78d..292d6a10b0c2 100644 --- a/include/linux/bug.h +++ b/include/linux/bug.h @@ -13,6 +13,7 @@ enum bug_trap_type { struct pt_regs; #ifdef __CHECKER__ +#define __BUILD_BUG_ON_NOT_POWER_OF_2(n) (0) #define BUILD_BUG_ON_NOT_POWER_OF_2(n) (0) #define BUILD_BUG_ON_ZERO(e) (0) #define BUILD_BUG_ON_NULL(e) ((void*)0) @@ -24,6 +25,8 @@ struct pt_regs; #else /* __CHECKER__ */ /* Force a compilation error if a constant expression is not a power of 2 */ +#define __BUILD_BUG_ON_NOT_POWER_OF_2(n) \ + BUILD_BUG_ON(((n) & ((n) - 1)) != 0) #define BUILD_BUG_ON_NOT_POWER_OF_2(n) \ BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0)) -- 1.9.1