Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756645Ab3GWKYK (ORCPT ); Tue, 23 Jul 2013 06:24:10 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:38360 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756183Ab3GWKYJ (ORCPT ); Tue, 23 Jul 2013 06:24:09 -0400 Date: Tue, 23 Jul 2013 11:23:34 +0100 From: Catalin Marinas To: Sudeep KarkadaNagesha Cc: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Mark Rutland , Lorenzo Pieralisi , Russell King , Will Deacon , Mathieu Poirier Subject: Re: [PATCH v2 1/3] drivers: clocksource: configure event stream for ARM arch timer Message-ID: <20130723102334.GC3748@MacBook-Pro.local> References: <1371575223-21702-1-git-send-email-Sudeep.KarkadaNagesha@arm.com> <1374492082-13686-1-git-send-email-Sudeep.KarkadaNagesha@arm.com> <1374492082-13686-2-git-send-email-Sudeep.KarkadaNagesha@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1374492082-13686-2-git-send-email-Sudeep.KarkadaNagesha@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1157 Lines: 32 On Mon, Jul 22, 2013 at 12:21:20PM +0100, Sudeep KarkadaNagesha wrote: > From: Will Deacon > > The ARM architected timer can generate events (used for waking up > CPUs executing the wfe instruction) at a frequency represented as a > power-of-2 divisor of the clock rate. > > This patch configures the event stream, aiming for a period of 100us > between events. This can be used to implement wfe-based timeouts for > userspace locking implementations. ... > --- a/include/clocksource/arm_arch_timer.h > +++ b/include/clocksource/arm_arch_timer.h > @@ -29,6 +29,8 @@ > #define ARCH_TIMER_PHYS_ACCESS 0 > #define ARCH_TIMER_VIRT_ACCESS 1 > > +#define ARCH_TIMER_EVT_STREAM_FREQ 10000 /* 100us */ BTW, if user-space starts using this, it will become an ABI. Is this the right frequency? In addition, do we want to expose this via hwcap? Something like HWCAP_EVSTR100US? -- Catalin -- 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/