From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752785Ab3EUJ2M (ORCPT ); Tue, 21 May 2013 05:28:12 -0400 Received: from intranet.asianux.com ([58.214.24.6]:36773 "EHLO intranet.asianux.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751005Ab3EUJ2K (ORCPT ); Tue, 21 May 2013 05:28:10 -0400 X-Spam-Score: -100.7 Message-ID: <519B3DF8.9060902@asianux.com> Date: Tue, 21 May 2013 17:27:20 +0800 From: Chen Gang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Will Deacon CC: Marc Zyngier , Catalin Marinas , Santosh Shilimkar , Tony Lindgren , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] arm64: kernel: compiling issue, need 'EXPORT_SYMBOL_GPL(read_current_timer)' References: <5199C725.8050102@asianux.com> <168084c28e8ba5124c05553e97463172@localhost> <20130520095606.GH31359@mudshark.cambridge.arm.com> <519AF2DC.2040200@asianux.com> <20130521085325.GB10453@mudshark.cambridge.arm.com> In-Reply-To: <20130521085325.GB10453@mudshark.cambridge.arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/21/2013 04:53 PM, Will Deacon wrote: > On Tue, May 21, 2013 at 05:06:52AM +0100, Chen Gang wrote: >> On 05/20/2013 05:56 PM, Will Deacon wrote: >>> Should be ok once the arch timer driver has moved exclusively to virtual >>> time. I'm also not sure we even need to implement read_current_timer() -- >>> it's only used for delay-loop calibration, which we don't need for the >>> arch timer. >>> >> >> For whether we need implement read_current_timer(): >> >> many platforms have implemented it (openrisc, arm, sparc, hexagon, avr32, x86). >> it is called by init/calibrate.c when 'ARCH_HAS_READ_CURRENT_TIMER' is defined. >> since arm64 can implement it, better to provide it as an architect features to let outside use. > > No, that code is not needed on arm64 because we calibrate the delay loop > statically using a known timer frequency. > >> For the implementation of read_current_timer(): >> >> it has to face various configurations >> (e.g. CONFIG_ARM_ARCH_TIMER, arch_timer_read_zero, arch_counter_get_cntvct, arch_counter_get_cntpct) >> so better still use variable instead of. >> (excuse me, I do not know what is 'CNTVCT_EL0', is it like a constant number ?) > > cntvct_el0 is a system register, which provides the virtual counter value. > >> For the implementation of get_cycles() >> >> if read_current_timer() is provided, >> better to let get_cycles() to call it, instead of implement once again. > > You can implement it as a macro if you like, I'm just suggesting that we > might not need read_current_timer after all. > > Will > > Thanks, I should try patch v2. :-) -- Chen Gang Asianux Corporation