From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nishanth Menon Subject: Re: [PATCH] save and restore etm state across core OFF modes Date: Wed, 13 Jan 2010 06:58:28 -0600 Message-ID: <4B4DC374.1010909@gmail.com> References: <1263315891-4440-1-git-send-email-virtuoso@slind.org> <4B4CADA9.4020502@ti.com> <20100112173022.GG29059@shisha.kicks-ass.net> <4B4CB259.2010301@ti.com> <20100112210404.GB2986@atomide.com> <20100112214654.GH29059@shisha.kicks-ass.net> <4B4CF2D7.9000200@ti.com> <20100113113616.GI29059@shisha.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-yx0-f187.google.com ([209.85.210.187]:64532 "EHLO mail-yx0-f187.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754886Ab0AMM6c (ORCPT ); Wed, 13 Jan 2010 07:58:32 -0500 Received: by yxe17 with SMTP id 17so22500123yxe.33 for ; Wed, 13 Jan 2010 04:58:31 -0800 (PST) In-Reply-To: <20100113113616.GI29059@shisha.kicks-ass.net> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Nishanth Menon , Tony Lindgren , Kevin Hilman , "linux-omap@vger.kernel.org" , Woodruff, Richard Alexander Shishkin said the following on 01/13/2010 05:36 AM: > On Tue, Jan 12, 2010 at 04:08:23 -0600, Nishanth Menon wrote: > >> Alexander Shishkin had written, on 01/12/2010 03:46 PM, the following: >> >>> On Tue, Jan 12, 2010 at 01:04:04 -0800, Tony Lindgren wrote: >>> >>>> * Nishanth Menon [100112 09:31]: >>>> >>>>> Alexander Shishkin had written, on 01/12/2010 11:30 AM, the following: >>>>> >>>>>> On Tue, Jan 12, 2010 at 11:13:13 -0600, Nishanth Menon wrote: >>>>>> >>>>>>> Alexander Shishkin had written, on 01/12/2010 11:04 AM, the following: >>>>>>> >>>>>>>> diff --git a/arch/arm/mach-omap2/sleep34xx.S b/arch/arm/mach-omap2/sleep34xx.S >>>>>>>> index 69521be..0a5ec86 100644 >>>>>>>> --- a/arch/arm/mach-omap2/sleep34xx.S >>>>>>>> +++ b/arch/arm/mach-omap2/sleep34xx.S >>>>>>>> >>>>> [...] >>>>> >>>>>>>> /* Store current cpsr*/ >>>>>>>> mrs r2, cpsr >>>>>>>> stmia r8!, {r2} >>>>>>>> @@ -520,6 +616,7 @@ clean_caches: >>>>>>>> cmp r9, #1 /* Check whether L2 inval is required or not*/ >>>>>>>> bne skip_l2_inval >>>>>>>> clean_l2: >>>>>>>> +#if 0 >>>>>>>> >>>>>>> my aversion to #if 0 kicks in here :(.. do we have an alternative >>>>>>> like using the CONFIG_ENABLE_OFF_MODE_JTAG_ETM_DEBUG or something >>>>>>> else? >>>>>>> >>>>>> Fair enough. I could replace it with "#if !defined(...)" as the first >>>>>> thing that comes to mind. This way it will only take disabling the >>>>>> config option to catch any possible regressions in between. Does this >>>>>> sound reasonable? >>>>>> >>>>> sounds ok to me.. unless folks have ideas coz of clean_l2 label.. >>>>> more comments might be useful before a rev2 of the patch.. >>>>> >>>> The best solution would be to be able to toggle this via sysfs or >>>> debugfs by swapping the sram code for idle loop when JTAG support >>>> is needed. >>>> >>> Well, if you say, compile the ETM driver in, this will be needed most of >>> the time. >>> >>> >> I can think of reasons for an against a sysfs entry (as part of >> discussion -warning lot of self contradictions below- but I think >> might save a bit of back and froth ;)): >> >> for sysfs entry: >> a) save and restore will have additional latency when you save a >> chunk such as EMU domain regs - this will not be needed in >> production phones, disabling it might pop up surprises >> counter: having a disabled defconfig allows relevant folks to >> enable on a need basis >> counter to counter: what do you do when a user reports >> an issue in a release and you'd want to debug it with >> ETM on his platform other than doing a rebuild? >> > > Well, my intention is to have it enabled for most of the cases only having > it disabled for testing purposes. > with a sysfs you can go either way, with proper #ifdeferry, you can get the best of all worlds I guess.. I know in one of the products, a similar patch was not taken in due to introduction of additional scratchpad space and latencies - so there are folks who would like this and those who would like to see this not present in the binary they flash to thier device. > >> b) mostly a debug support -> only for blokes using ETM/JTAG >> interfaces - not everyone can afford these (no offense to openOCD >> guys - but they are still a bit away from being able to debug kernel >> yet on OMAP).. >> > > Not really, you can still make use of ETM without any additional hardware > attached. For the unitiated (like me) link from Alex's offline email[1]. Regards, Nishanth Menon [1] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=c5d6c7708c3e58015b2e4e13e6cea02c8567a94e