Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758253Ab0LTWUh (ORCPT ); Mon, 20 Dec 2010 17:20:37 -0500 Received: from wolverine01.qualcomm.com ([199.106.114.254]:33070 "EHLO wolverine01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758078Ab0LTWUg (ORCPT ); Mon, 20 Dec 2010 17:20:36 -0500 X-IronPort-AV: E=McAfee;i="5400,1158,6203"; a="67616905" From: Stephen Boyd To: Russell King - ARM Linux Cc: linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Saravana Kannan , Daniel Walker , Nicolas Pitre , John Stultz , Brian Swetland , =?UTF-8?q?Arve=20Hj=F8nnev=E5g?= , Andrew Morton Subject: [PATCHv4 0/4] ARM: Fixing udelay() for SMP and non-SMP systems Date: Mon, 20 Dec 2010 14:20:29 -0800 Message-Id: <1292883633-19553-1-git-send-email-sboyd@codeaurora.org> X-Mailer: git-send-email 1.7.3.4.516.g15368e Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2646 Lines: 62 These patches fix the udelay() issue pointed out on arm-lkml[1][2]. A quick recap: some SMP machines can scale their CPU frequencies independent of one another. loops_per_jiffy is calibrated globally and used in __const_udelay(). If one CPU is running faster than what the loops_per_jiffy is calculated (or scaled) for, udelay() will be incorrect and not wait long enough (or too long). A similar problem occurs if the cpu frequency is scaled during a udelay() call. We could fix this issue a couple ways, wholesale replacement of __udelay() and __const_udelay() (see [2] for that approach), or replacement of __delay() (this series). Option 1 can fail if anybody uses udelay() before memory is mapped and also duplicates most of the code in asm/delay.h. It also needs to hardcode the timer tick frequency, which can sometimes be inaccurate. The benefit is that loops_per_jiffy stays the same and thus BogoMIPS is unchanged. Option 2 can't fail since the __delay() loop is replaced after memory is mapped in, but it suffers from a low BogoMIPS when timers are clocked slowly. It also more accurately calculates the timer tick frequency through the use of calibrate_delay_direct(). -- Reference -- [1] http://article.gmane.org/gmane.linux.kernel/977567 [2] http://article.gmane.org/gmane.linux.ports.arm.kernel/78496 Changes since v3: * Inlined set_delay_fn() Changes since v2: * Additional patch using the timer based delay Changes since v1: * likely() in delay.c * comment fixup for read_current_timer_delay_loop() * cosmetic improvements to commit text Stephen Boyd (4): ARM: Translate delay.S into (mostly) C ARM: Allow machines to override __delay() ARM: Implement a timer based __delay() loop msm: timer: Migrate to timer based __delay() arch/arm/include/asm/delay.h | 11 ++++- arch/arm/kernel/armksyms.c | 4 -- arch/arm/lib/delay.S | 65 ------------------------- arch/arm/lib/delay.c | 81 ++++++++++++++++++++++++++++++++ arch/arm/mach-msm/include/mach/timex.h | 1 + arch/arm/mach-msm/timer.c | 16 ++++++- 6 files changed, 107 insertions(+), 71 deletions(-) delete mode 100644 arch/arm/lib/delay.S create mode 100644 arch/arm/lib/delay.c -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/