From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH] xen/arm: Blacklist the memory mapped timer (armv7-timer-mem) Date: Wed, 14 Jan 2015 16:06:55 +0000 Message-ID: <1421251615.19103.289.camel@citrix.com> References: <1421179673-30754-1-git-send-email-julien.grall@linaro.org> <1421233321.19103.215.camel@citrix.com> <54B69369.6000707@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YBQaU-0002Xm-OW for xen-devel@lists.xenproject.org; Wed, 14 Jan 2015 16:14:30 +0000 In-Reply-To: <54B69369.6000707@linaro.org> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Julien Grall Cc: xen-devel@lists.xenproject.org, tim@xen.org, stefano.stabellini@citrix.com List-Id: xen-devel@lists.xenproject.org On Wed, 2015-01-14 at 16:03 +0000, Julien Grall wrote: > Hi Ian, > > On 14/01/15 11:02, Ian Campbell wrote: > > On Tue, 2015-01-13 at 20:07 +0000, Julien Grall wrote: > >> Some platform (such as the VFP Base AEMv8 model) has a memory mapped > >> timer. We don't want DOM0 use this timer rather than the generic ARM > >> timer. So blacklist it for all platforms. > > > > It seems that these registers contain things like the ability to stop > > the counter or change its frequency. So we certainly don't want dom0 > > getting at those! > > > > It's not clear to me if accesses to these registers are trapped > > according to the controls available for the CP registers, or if we would > > have to resort to trapping the entire MMIO page if we wanted to support > > access to these registers (I don't think we would want to anyway). > > I didn't find any spec for the memory mapped timer. But looking to the > driver, it looks like they also have the concept of physical/virtual. So > we may not need to trap. > > Anyway, before implementing anything I'd like to find the corresponding > spec. It's in the ARM ARM, Appendix E of v7, plus references from Chapter B8. I'd imagine it was in the v8 ARM ARM too, but I've not looked. Ian.