From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261705AbTHTEqf (ORCPT ); Wed, 20 Aug 2003 00:46:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261714AbTHTEqf (ORCPT ); Wed, 20 Aug 2003 00:46:35 -0400 Received: from fmr01.intel.com ([192.55.52.18]:3227 "EHLO hermes.fm.intel.com") by vger.kernel.org with ESMTP id S261705AbTHTEqc convert rfc822-to-8bit (ORCPT ); Wed, 20 Aug 2003 00:46:32 -0400 content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-MimeOLE: Produced By Microsoft Exchange V6.0.6375.0 Subject: [PATCHSET][2.6][0/5]Support for HPET based timer - Take 1 Date: Tue, 19 Aug 2003 18:16:07 -0700 Message-ID: X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [PATCHSET][2.6][0/5]Support for HPET based timer - Take 1 Thread-Index: AcNmuKInHcx89LsYQGaKo2u9yMILRg== From: "Pallipadi, Venkatesh" To: Cc: , "Nakajima, Jun" , "Mallick, Asit K" X-OriginalArrivalTime: 20 Aug 2003 01:16:08.0112 (UTC) FILETIME=[A2661300:01C366B8] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org [Resend - The original mail hasn't yet appeared on lkml, even 5 hours after posting] High Precision Event Timer (HPET) is next generation timer hardware and has various advantages over legacy 8254 (PIT) timer, like: - Associated registers are mapped to memory space. So, we no longer require in and out on legacy ioports - Memory map address is reported by ACPI (and are not hard-coded) - Each timer can be configured to generate separate interrupts, even sharing lines with PCI devices - HPET has a minimum period of 100 nanosecs and is not fixed. Giving a flexibility of increasing the resolution in future. - Most current implementations has 3 counters, but in future, we can have as many as 32 timers per block, and 8 HPET timer blocks (total 256 timers) - Can support 32bit and 64bit counting (Refer to http://www.intel.com/labs/platcomp/hpet/hpetspec.htm for complete specs) The patchset that follow adds support for High Precision Event Timer (HPET) based timer in kernel. This uses the HPET in LegacyReplacement mode (so that counter 0 will be tied to IRQ0, and counter 1 will be tied to IRQ 8). In this mode, HPET overrides PIT and RTC interrupt lines. The patch will enable HPET by default, on systems where ACPI tables reports this feature. The patch will have no impact on systems that do not support this feature. Patchset description: 1/5 - hpet1.patch - acpi boot time parsing changes to look for HPET 2/5 - hpet2.patch - All the changes required to use HPET in place of PIT as the kernel base-timer at IRQ 0. 3/5 - hpet3.patch - All changes required to support timer services (gettimeofday) with HPET. There are two options: - Use HPET for gettimeofday. - Use rdtsc for gettimeofday. rdtsc is still faster then HPET reads, but HPET has advantage that its rate remain same, irrespective of CPU frequency. Also, HPET is more scalable than TSC in case of multi-node systems. So, our timer priority is platform_specific_timer(if any), timer_hpet and timer_tsc in that order. 4/5 - hpet4.patch - Miscallaneous makefile and config changes 5/5 - hpet5.patch - This can be a standalone patch. Without this patch we loose interrupt generation capability of RTC (/dev/rtc), due to HPET. With this patch we basically try to emulate RTC interrupt functions in software using HPET counter 1. This is only required to provide compatibility to the applications that depend on rtc driver's interrupt generation capability. This emulation will not be as accurate as RTC interrupt, as HPET is not tied to RTC hardware and does not know anything about RTC time. But should enough for compatibility purposes. All comments/feedbacks welcome. Thanks, -Venkatesh