linux-kernel - Re: [PATCH] clocksource: dw_apb_timer

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Message-ID: <20151103174534.2c9f5eeb@xhacker>
Date:	Tue, 3 Nov 2015 17:45:34 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	<tglx@...utronix.de>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clocksource: dw_apb_timer_of: support timer-based delay

Dear Arnd

On Tue, 3 Nov 2015 09:49:32 +0100
Arnd Bergmann wrote:

> On Tuesday 03 November 2015 14:59:40 Jisheng Zhang wrote:
> > > On Monday 02 November 2015 11:03:34 Jisheng Zhang wrote:  
> > > > On Fri, 30 Oct 2015 13:42:01 +0100 Arnd Bergmann wrote:    
> > > I'd be happier with a solution that keeps the DT describing the hardware
> > > and not the way we expect Linux to use it, and instead has some heuristic
> > > in the selection of the delay timer. At the moment, we purely base this
> > > on the frequency, which as you say is suboptimal.
> > > 
> > > One possible way to improve this would be to add an optional 'latency'
> > > property to the DT nodes (or the driver), and use a combination of latency
> > > and resolution to make the decision.  
> > 
> > Got it. Thanks for the suggestions. The 'latency' here seems a 'rating'
> > similar as the one in clocksource. I will cook a series for review:
> > 
> > patch 1 to make register_current_timer_delay() aware of 'rating'
> > 
> > patch 2 to set rating of arch timer as 400
> > 
> > patch 3 to add timer based delay support to dw_apb_timer whose rating is 300  
> 
> Ok. Just to make sure I got this right: your plan is to use the existing
> 'rating' setting as a primary indication, and fall back to comparing the
> frequency if the rating is the same?

Yes, this is my plan.

Thanks,
Jisheng
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