linux-kernel - Re: [PATCH RT 11/20] ARM: imx: always use TWD on IMX6Q

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Message-ID: <578D0F83.2010403@ti.com>
Date:	Mon, 18 Jul 2016 20:18:59 +0300
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
CC:	<linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>,
	John Kacur <jkacur@...hat.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH RT 11/20] ARM: imx: always use TWD on IMX6Q

On 07/12/2016 11:04 PM, Sebastian Andrzej Siewior wrote:
> * Steven Rostedt | 2016-07-12 10:24:16 [-0400]:
> 
>> 4.1.27-rt31-rc1 stable review patch.
>> If anyone has any objections, please let me know.
> 
> I don't recommend to cherry-pick this. The symbol it selects
> (HAVE_ARM_TWD) has "depends on SMP" in v4.1. In v4.4 there should be
> AM43xx which is UP and also uses the TWD so the change is simple here.
> 

yes. AM43xx is UP and supports ARM TWD, but there could be some 'issues' in !RT case :(

ARM TWD might be powered off in deep CPU Idle states and lose its context if !RT & CPUIDLE,
so there are should be backup broadcast timer configured. And that can cause build issues
related to tick_broadcast()->smp_cross_call().

I've solved it locally for OMAP2 only: commit 0b3e6fca4d1af4aa150d32506220f4241323a00c

^Just FYI. But may be it can be done in more generic way.

regards,
-grygorii