From owner-freebsd-sparc64@FreeBSD.ORG Wed Jun 29 22:32:22 2011 Return-Path: Delivered-To: freebsd-sparc64@FreeBSD.org Received: from [127.0.0.1] (freefall.freebsd.org [IPv6:2001:4f8:fff6::28]) by hub.freebsd.org (Postfix) with ESMTP id 31C221065670; Wed, 29 Jun 2011 22:32:22 +0000 (UTC) (envelope-from jkim@FreeBSD.org) From: Jung-uk Kim To: Marius Strobl Date: Wed, 29 Jun 2011 18:32:11 -0400 User-Agent: KMail/1.6.2 References: <201106281327.02537.jkim@FreeBSD.org> <201106281337.54901.jkim@FreeBSD.org> <20110629205646.GK14797@alchemy.franken.de> In-Reply-To: <20110629205646.GK14797@alchemy.franken.de> MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201106291832.13735.jkim@FreeBSD.org> Cc: freebsd-sparc64@FreeBSD.org Subject: Re: [RFC] Clean up sparc64 timecounters X-BeenThere: freebsd-sparc64@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Porting FreeBSD to the Sparc List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 29 Jun 2011 22:32:22 -0000 On Wednesday 29 June 2011 04:56 pm, Marius Strobl wrote: > On Tue, Jun 28, 2011 at 01:37:52PM -0400, Jung-uk Kim wrote: > > On Tuesday 28 June 2011 01:26 pm, Jung-uk Kim wrote: > > > Can you please review the attached patch? > > > > > > sys/sparc64/pci/fire.c: > > > - Remove redundant timecounter masking from tc_get_timecount > > > method. - Remove an unnecessary macro for timecounter mask. > > > - Remove a redundant NULL assignment. > > > > > > sys/sparc64/pci/schizo.c: > > > - Remove redundant timecounter masking from tc_get_timecount > > > method. - Correct timecounter mask. Note this is a no-op > > > because the STX_CTRL_PERF_CNT_CNT0_SHIFT is actually zero. > > > - Remove a redundant NULL assignment. > > I'm not sure whether you correctly understand how that timer works. > The hardware actually provides a pair of 32-bit timers which are > read via a single 64-bit register so the existing tc_counter_mask > is correct and your change is wrong. For the same reason the > masking and shifting in schizo_get_timecount() only happens to be > unnecessary in so far as we currently use the lower 32-bit counter > and the tc_get_timecount methods return u_int. Actually, tc_counter_mask is also u_int and the upper 32-bit is always ignored. > If we'd either switch to the upper 32-bit counter or the timecounter > code would be enhanced to support up to 64-bit counters it wouldn't > be redundant. There is no reason to support 64-bit timecounter as kern_tc.c was meant to be MI code. > There's actually a right-shift missing in schizo_get_timecount() > though, i.e. it should actually do: > return ((SCHIZO_CTRL_READ_8(sc, STX_CTRL_PERF_CNT) & > (STX_CTRL_PERF_CNT_MASK << STX_CTRL_PERF_CNT_CNT0_SHIFT) >> > STX_CTRL_PERF_CNT_CNT0_SHIFT); > The compiler should be smart enough to boil all that down to a > single 64-bit to 32-bit conversion when returning though. tc_get_timecount method should return a raw value. There is no reason to mask it here because kern_tc.c does it whenever necessary. > For similar reasons I'd prefer to also keep the masking in > fire_get_timecount(), besides using the macro IMO is cleaner > than using ~0u(l). Please see above. tc_counter_mask is u_int. Jung-uk Kim > > @@ -686,8 +684,7 @@ fire_attach(device_t dev) > > if (tc == NULL) > > panic("%s: could not malloc timecounter", > > __func__); tc->tc_get_timecount = fire_get_timecount; - > > tc->tc_poll_pps = NULL; > > - tc->tc_counter_mask = TC_COUNTER_MAX_MASK; > > + tc->tc_counter_mask = ~0ul; > > ^^^^ > > ~0u > > if (OF_getprop(OF_peer(0), "clock-frequency", > > &prop, sizeof(prop)) == -1) > > panic("%s: could not determine clock > > frequency", > > Well, if you really remove the masking from fire_get_timecount() > then you should actually also use ~0ul here for consistency as it's > an 64-bit counter. > > Marius