Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753490Ab3DKLYd (ORCPT ); Thu, 11 Apr 2013 07:24:33 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:57357 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751434Ab3DKLYc (ORCPT ); Thu, 11 Apr 2013 07:24:32 -0400 Date: Thu, 11 Apr 2013 12:24:07 +0100 From: Mark Rutland To: Stephen Boyd Cc: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-arm-msm@vger.kernel.org" , "devicetree-discuss@lists.ozlabs.org" , Marc Zyngier Subject: Re: [PATCH 1/4] Documentation: Add memory mapped ARM architected timer binding Message-ID: <20130411112407.GD8259@e106331-lin.cambridge.arm.com> References: <1365474623-29181-1-git-send-email-sboyd@codeaurora.org> <1365474623-29181-2-git-send-email-sboyd@codeaurora.org> <20130409090843.GS23725@e106331-lin.cambridge.arm.com> <516444FE.2080200@codeaurora.org> <20130410101336.GB8799@e106331-lin.cambridge.arm.com> <51662584.6070906@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51662584.6070906@codeaurora.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3356 Lines: 82 On Thu, Apr 11, 2013 at 03:52:52AM +0100, Stephen Boyd wrote: > On 04/10/13 03:13, Mark Rutland wrote: > >>>> + > >>>> +- #size-cells : Must be 1. > >>>> + > >>>> +- ranges : Indicates parent and child bus address space are the same. > >>>> + > >>> Similarly, what if someone wants to write a more complex mapping for some > >>> reason? > >>> > >>> We should be able to handle it if we use the standard accessors. > >> Maybe I should just leave this part out? They are standard DT properties > >> so I could assume DT writers know what to do. > > I'd be happy with that. It may be worth describing them as "as necessary" or > > something to that effect. > > Ok. I added this and removed the property descriptions: > > Note that #address-cells, #size-cells, and ranges shall be present to ensure > the CPU can address a frame's registers. Sounds good to me. > > > I can see why we need to specify secure/non-secure, but I'm not sure why we > > need to specify hyp/user/kernel usage. Could we not leave this up to the kernel > > to figure out? > > > > A basic overveiew for those that don't know about the memory mapped timers: > > > > * There's one control frame CNTCTLBase. Some registers in this frame are only > > available for secure accesses, including CNTNSAR which sets whether the > > counter frames are accessible from the non-secure side. > > > > * There are up to 8 timer frames, which have their own CNTVOFF and > > physical/virtual timers. Each frame CNTBaseN is duplicated at CNTPL0BaseN > > with CNTVOFF and CNTPL0ACR (which controls PL0 accesses) inaccessible. > > > > I can see that we might have frames/registers we can't access (if we were > > booted on the non-secure side), but I can't see anything limiting whether we > > use a frame for kernel/hyp/user beyond that. Have I missed something? > > > > Could we not have something like the following for each frame: > > > > frame0 { > > frame-id = <0>; > > status = "disabled"; /* booted NS, secure firmware has not enabled access */ > > reg = <0x... 0x1000>, /* CNTBase0 */ > > <0x... 0x1000>; /* CNTPL0Base0 */ > > }; > > > > I don't think you're missing anything. Technically the second view is > not always implemented though. Using the status property should be > sufficient I think. Could we say the reg for the second view is optional? Might we have a hardware / firmware configuration where the kernel can only access the secondary view? > > >> Also to get the frame number, I was thinking maybe we should expand the > >> reg property to have two address cells. Then we could have reg = <0 > >> 0xf0001000 0x1000>. > > We could do that, but then you definitely need a more complex ranges property, > > and additional parsing code to handle grabbing it out of the reg property. I > > can't see what it buys us. > > Ok. It would mandate node names like "frame@0", "frame@1", but I'll drop > the idea unless someone else finds it useful. I see. I'd prefer to use a separate property for the id. Placing it in the reg and then requiring a mapping sounds like it's going to cause a lot of pain. Cheers, Mark. -- 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/