From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from wolverine02.qualcomm.com ([199.106.114.251]:12999 "EHLO wolverine02.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750698Ab0LHEiz (ORCPT ); Tue, 7 Dec 2010 23:38:55 -0500 From: Stephen Boyd Subject: [PATCHv3 0/4] ARM: Fixing udelay() for SMP and non-SMP systems Date: Tue, 7 Dec 2010 20:38:44 -0800 Message-Id: <1291783128-27520-1-git-send-email-sboyd@codeaurora.org> Sender: linux-arm-msm-owner@vger.kernel.org List-ID: To: Russell King - ARM Linux Cc: linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Daniel Walker , Saravana Kannan , Nicolas Pitre , John Stultz , Brian Swetland , =?UTF-8?q?Arve=20Hj=F8nnev=E5g?= These patches fixing 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(). Russell, I'm planning on submitting these to the patch queue unless I hear objections. 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 | 5 ++- arch/arm/kernel/armksyms.c | 4 -- arch/arm/lib/delay.S | 65 ------------------------ arch/arm/lib/delay.c | 86 ++++++++++++++++++++++++++++++++ arch/arm/mach-msm/include/mach/timex.h | 1 + arch/arm/mach-msm/timer.c | 16 ++++++- 6 files changed, 106 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.