Return-path: Received: from mail-wm0-f43.google.com ([74.125.82.43]:37815 "EHLO mail-wm0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752537AbcGAV1W (ORCPT ); Fri, 1 Jul 2016 17:27:22 -0400 Received: by mail-wm0-f43.google.com with SMTP id a66so44452951wme.0 for ; Fri, 01 Jul 2016 14:27:21 -0700 (PDT) From: Jakub Kicinski To: kvalo@codeaurora.org, linux-wireless@vger.kernel.org Cc: netdev@vger.kernel.org, hannes@stressinduktion.org, nbd@nbd.name, linux-kernel@vger.kernel.org, Jakub Kicinski Subject: [PATCHv3 wl-drv-next 1/2] add basic register-field manipulation macros Date: Fri, 1 Jul 2016 22:26:48 +0100 Message-Id: <1467408409-24224-2-git-send-email-jakub.kicinski@netronome.com> (sfid-20160701_232817_743879_C29FFAD1) In-Reply-To: <1467408409-24224-1-git-send-email-jakub.kicinski@netronome.com> References: <1467408409-24224-1-git-send-email-jakub.kicinski@netronome.com> Sender: linux-wireless-owner@vger.kernel.org List-ID: C bitfields are problematic and best avoided. Developers interacting with hardware registers find themselves searching for easy-to-use alternatives. Common approach 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. Signed-off-by: Jakub Kicinski --- include/linux/bitfield.h | 58 ++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/bug.h | 3 +++ 2 files changed, 61 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..d6a36c3c1775 --- /dev/null +++ b/include/linux/bitfield.h @@ -0,0 +1,58 @@ +/* + * 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 +#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))); \ + }) + +#define FIELD_PUT(_mask, _val) \ + ({ \ + _BF_FIELD_CHECK(_mask, _val); \ + ((u32)(_val) << _bf_shf(_mask)) & (_mask); \ + }) + +#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