Return-path: Received: from mail-wm0-f54.google.com ([74.125.82.54]:38635 "EHLO mail-wm0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753626AbcHPPS4 (ORCPT ); Tue, 16 Aug 2016 11:18:56 -0400 Received: by mail-wm0-f54.google.com with SMTP id o80so175142368wme.1 for ; Tue, 16 Aug 2016 08:18:55 -0700 (PDT) From: Jakub Kicinski To: torvalds@linux-foundation.org, akpm@linux-foundation.org, gregkh@linuxfoundation.org, davem@davemloft.net, kvalo@codeaurora.org Cc: linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org, dinan.gunawardena@netronome.com, Jakub Kicinski Subject: [PATCHv6 1/2] add basic register-field manipulation macros Date: Tue, 16 Aug 2016 16:18:23 +0100 Message-Id: <1471360704-10507-2-git-send-email-jakub.kicinski@netronome.com> (sfid-20160816_171936_040526_EA44652A) In-Reply-To: <1471360704-10507-1-git-send-email-jakub.kicinski@netronome.com> References: <1471360704-10507-1-git-send-email-jakub.kicinski@netronome.com> Sender: linux-wireless-owner@vger.kernel.org List-ID: Common approach to accessing register fields is to define structures or sets of macros containing mask and shift pair. Operations on the register are then performed as follows: field = (reg >> shift) & mask; reg &= ~(mask << shift); reg |= (field & mask) << shift; Defining shift and mask separately is tedious. Ivo van Doorn came up with an idea of computing them at compilation time based on a single shifted mask (later refined by Felix) which can be used like this: #define REG_FIELD 0x000ff000 field = FIELD_GET(REG_FIELD, reg); reg &= ~REG_FIELD; reg |= FIELD_PUT(REG_FIELD, field); FIELD_{GET,PUT} macros take care of finding out what the appropriate shift is based on compilation time ffs operation. GENMASK can be used to define registers (which is usually less error-prone and easier to match with datasheets). This approach is the most convenient I've seen so to limit code multiplication let's move the macros to a global header file. Attempts to use static inlines instead of macros failed due to false positive triggering of BUILD_BUG_ON()s, especially with GCC < 6.0. Signed-off-by: Jakub Kicinski Reviewed-by: Dinan Gunawardena --- include/linux/bitfield.h | 109 +++++++++++++++++++++++++++++++++++++++++++++++ include/linux/bug.h | 3 ++ 2 files changed, 112 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..ff9fd0af2ac7 --- /dev/null +++ b/include/linux/bitfield.h @@ -0,0 +1,109 @@ +/* + * 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 +#include + +#define _bf_shf(x) (__builtin_ffsll(x) - 1) + +#define _BF_FIELD_CHECK(_mask, _val) \ + ({ \ + BUILD_BUG_ON(!(_mask)); \ + BUILD_BUG_ON(__builtin_constant_p(_val) ? \ + ~((_mask) >> _bf_shf(_mask)) & (_val) : \ + 0); \ + __BUILD_BUG_ON_NOT_POWER_OF_2((_mask) + \ + (1ULL << _bf_shf(_mask))); \ + }) + +/* + * Bitfield access macros + * + * This file contains macros which take as input shifted mask + * from which they extract the base mask and shift amount at + * compilation time. There are two separate sets of the macros + * one for 32bit registers and one for 64bit ones. + * + * Fields can be defined using GENMASK (which is usually + * less error-prone and easier to match with datasheets). + * + * FIELD_{GET,PUT} macros are designed to be used with masks which + * are compilation time constants. + * + * 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_PUT(REG_FIELD_A, 1) | + * FIELD_PUT(REG_FIELD_B, 0) | + * FIELD_PUT(REG_FIELD_C, c) | + * FIELD_PUT(REG_FIELD_D, 0x40); + * + * Modify: + * reg &= ~REG_FIELD_C; + * reg |= FIELD_PUT(REG_FIELD_C, c); + */ + +/** + * FIELD_PUT() - construct a bitfield element + * @_mask: shifted mask defining the field's length and position + * @_val: value to put in the field + * + * FIELD_PUT() masks and shifts up the value. The result should + * be combined with other fields of the bitfield using logical OR. + */ +#define FIELD_PUT(_mask, _val) \ + ({ \ + _BF_FIELD_CHECK(_mask, _val); \ + ((u32)(_val) << _bf_shf(_mask)) & (_mask); \ + }) + +/** + * FIELD_GET() - extract a bitfield element + * @_mask: shifted mask defining the field's length and position + * @_val: 32bit value of entire bitfield + * + * FIELD_GET() extracts the field specified by @_mask from the + * bitfield passed in as @_val. + */ +#define FIELD_GET(_mask, _val) \ + ({ \ + _BF_FIELD_CHECK(_mask, 0); \ + (u32)(((_val) & (_mask)) >> _bf_shf(_mask)); \ + }) + +#define FIELD_PUT64(_mask, _val) \ + ({ \ + _BF_FIELD_CHECK(_mask, _val); \ + ((u64)(_val) << _bf_shf(_mask)) & (_mask); \ + }) + +#define FIELD_GET64(_mask, _val) \ + ({ \ + _BF_FIELD_CHECK(_mask, 0); \ + (u64)(((_val) & (_mask)) >> _bf_shf(_mask)); \ + }) + +#endif diff --git a/include/linux/bug.h b/include/linux/bug.h index e51b0709e78d..bba5bdae1681 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