From patchwork Mon Jun 13 13:29:53 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jakub Kicinski X-Patchwork-Id: 634647 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 3rStvb0YnPz9t10 for ; Mon, 13 Jun 2016 23:30:51 +1000 (AEST) Authentication-Results: ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=netronome-com.20150623.gappssmtp.com header.i=@netronome-com.20150623.gappssmtp.com header.b=rkLlFUAY; dkim-atps=neutral Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965524AbcFMNaR (ORCPT ); Mon, 13 Jun 2016 09:30:17 -0400 Received: from mail-wm0-f50.google.com ([74.125.82.50]:35527 "EHLO mail-wm0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965491AbcFMNaO (ORCPT ); Mon, 13 Jun 2016 09:30:14 -0400 Received: by mail-wm0-f50.google.com with SMTP id v199so78513556wmv.0 for ; Mon, 13 Jun 2016 06:30:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=netronome-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=KvhyWiprUAEqwzLfVqGPnqCN4F4JFVTNQeIkJuELTTQ=; b=rkLlFUAYO1mP4YvBxoeLvePCnCZzT1qZSc0fn9KX9utcf/Y56avO1oRATlAGMotQJ3 p6r3s96DgzRQz/X4Huub8rFcte9l6yzRiVGDaJO2/BMOJiBIKxogrdU9yNieVSJcLHy4 mZKto3+5Jfe02LMvPoB+2erz/P7Ofq1Tin7znVFWK/mbWOVCuoONkvLbORd9hfXxNDnb V7FhWIRZT9G/0zvDFCFe7YRQA0WQlZnh7e2olsXiI4fQBiHJOjfoG4d2ae6tv6ZUS6g7 ZOaB5OCGVPwGlw4za2w4qvAznn9e0nqx8qKtGQp0EOplY3StavQ2KUtN9esMjN902rHG rHRg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=KvhyWiprUAEqwzLfVqGPnqCN4F4JFVTNQeIkJuELTTQ=; b=ioNO/NqBYXTVGgckhVlaoya1P7mbCtIqf5FwBcKivPhr1SBMGF0n52FKFX00jTeiR7 W8cq1O/djk11yvlxJ/iVMi4A3TG+wScv+l5dVS3pPtX5Oddg63x9LB3QDFQ7mQ4TyAdl se9FX1gYlxtqEpHcMv6A3adAEAfPyOseebTxRssmv5s78ANZZHK/ReALc1GLJ8zO5H2j hHm6Ux8FIjJShCKcCITiAV7co0z4xOHMi8rUp9RC+DmY+JRK6pshkcl3/ypi7KSDoPDx fgrgAxDqDeoXR3iK51bTTKzmqIHj1BY5tNGsbTCqtoe4k+rpFkhuYzNMXC8IcP2F5W0K oyyA== X-Gm-Message-State: ALyK8tLTLHXF7gM+qjWivyF7gip8VOKZHMU+Ic62010Bba1y+rsG6hTdDk1ltD8IjP2sJpZY X-Received: by 10.28.8.17 with SMTP id 17mr1262044wmi.67.1465824612586; Mon, 13 Jun 2016 06:30:12 -0700 (PDT) Received: from jkicinski-Precision-T1700.netronome.com (host-79-78-33-110.static.as9105.net. [79.78.33.110]) by smtp.gmail.com with ESMTPSA id m5sm14419678wmm.10.2016.06.13.06.30.11 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 13 Jun 2016 06:30:12 -0700 (PDT) From: Jakub Kicinski To: netdev@vger.kernel.org Cc: hannes@stressinduktion.org, nbd@nbd.name, linux-kernel@vger.kernel.org, kvalo@codeaurora.org, Jakub Kicinski Subject: [PATCH 1/2] add basic register-field manipulation macros Date: Mon, 13 Jun 2016 14:29:53 +0100 Message-Id: <1465824594-29662-2-git-send-email-jakub.kicinski@netronome.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1465824594-29662-1-git-send-email-jakub.kicinski@netronome.com> References: <1465824594-29662-1-git-send-email-jakub.kicinski@netronome.com> Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 X_REG_FIELD 0x000ff000 field = FIELD_GET(X_REG_FIELD, reg); reg &= ~X_REG_FIELD; reg |= FIELD_PUT(X_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. Compared to Felix Fietkau's implementation from mt76 this one uses standard Linux and GCC functions such as is_power_of_2() and __builtin_ffsll(). Signed-off-by: Jakub Kicinski --- include/linux/bitfield.h | 58 ++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/log2.h | 6 +++++ 2 files changed, 64 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..ae2224464523 --- /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) \ + ({ \ + const u64 hi = (_mask) + (1ULL << _bf_shf(_mask)); \ + \ + BUILD_BUG_ON(!(_mask) || (hi && !is_power_of_2_u64(hi))); \ + BUILD_BUG_ON(__builtin_constant_p(_val) ? \ + ~((_mask) >> _bf_shf(_mask)) & (_val) : \ + 0); \ + }) + +#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/log2.h b/include/linux/log2.h index fd7ff3d91e6a..1b5e1f4da043 100644 --- a/include/linux/log2.h +++ b/include/linux/log2.h @@ -54,6 +54,12 @@ bool is_power_of_2(unsigned long n) return (n != 0 && ((n & (n - 1)) == 0)); } +static inline __attribute__((const)) +bool is_power_of_2_u64(u64 n) +{ + return (n != 0 && ((n & (n - 1)) == 0)); +} + /* * round up to nearest power of two */