Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932967AbbFCREU (ORCPT ); Wed, 3 Jun 2015 13:04:20 -0400 Received: from mail-ie0-f180.google.com ([209.85.223.180]:33074 "EHLO mail-ie0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753892AbbFCREN (ORCPT ); Wed, 3 Jun 2015 13:04:13 -0400 MIME-Version: 1.0 In-Reply-To: References: <1432194944-29087-1-git-send-email-adrian.hunter@intel.com> <20150603062054.GA23303@gmail.com> Date: Wed, 3 Jun 2015 10:04:12 -0700 X-Google-Sender-Auth: MTG2Tle1ktsgg7fwLbWmhDEll-8 Message-ID: Subject: Re: [PATCH RFC] x86, tsc: Allow for high latency in quick_pit_calibrate() From: Linus Torvalds To: Thomas Gleixner Cc: Ingo Molnar , Adrian Hunter , LKML , Andy Lutomirski , Andi Kleen , "the arch/x86 maintainers" , "H. Peter Anvin" , Len Brown Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1152 Lines: 30 On Wed, Jun 3, 2015 at 9:47 AM, Thomas Gleixner wrote: > >> Does anybody know what the base oscillator for HPET tends to be? Also, > > The most common frequency is 14.318180 MHz. I was more thinking along the lines of "which actually crystal is driving it" than the frequency. That said, that particular frequency does give a clue. That's exactly 12x the PIT frequency. So they presumably share the same basic crystal, just different PLL's. Which is a good indication that we should get very similar clock stability with the HPET as with the PIC. We might even use that kind of knowledge to decide "ok, let's use the HPET as the reference clock". IOW, only use the HPET if we find it listed, _and_ we get the expected frequency from the HPET_PERIOD register. Anybody who gives odd HPET_PERIOD values is likely doing somehing different and possibly questionable. Linus -- 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/