linux-kernel - RE: [PATCH 2/5] Clocksource: Flextimer: Use internal clocksource read API.

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Message-ID: <alpine.DEB.2.10.1409041032200.3333@nanos>
Date:	Thu, 4 Sep 2014 10:35:26 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Li.Xiubo@...escale.com" <Li.Xiubo@...escale.com>
cc:	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"Dongsheng.Wang@...escale.com" <Dongsheng.Wang@...escale.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/5] Clocksource: Flextimer: Use internal clocksource
 read API.

On Thu, 4 Sep 2014, Li.Xiubo@...escale.com wrote:

> > Subject: Re: [PATCH 2/5] Clocksource: Flextimer: Use internal clocksource read
> > API.
> > 
> > On Tue, 26 Aug 2014, Xiubo Li wrote:
> > 
> > > Since the Flextimer device will be implemented in BE mode on
> > > LS1 SoC, and in LE mode on Vybrid, LS2 SoCs, so here we need
> > > the endianness judgment before doing the mmio.
> > 
> > Brilliant. So for every clocksource read you take a conditional.
> > 
> > > @@ -238,7 +243,7 @@ static int __init ftm_clocksource_init(unsigned long
> > freq)
> > >  	sched_clock_register(ftm_read_sched_clock, 16, freq / (1 << priv->ps));
> > >  	err = clocksource_mmio_init(priv->clksrc_base + FTM_CNT, "fsl-ftm",
> > >  				    freq / (1 << priv->ps), 300, 16,
> > > -				    clocksource_mmio_readl_up);
> > > +				    ftm_clocksource_read_up);
> > 
> > What's wrong with having endianess aware clocksource_mmio functions
> > and make the decision at init time?
> > 
> 
> Since the FTM will be in BE mode on LS1 platform, but will be in LE mode
> On LS2 platform.
> 
> And ftm_clocksource_read_up() will adapt to this different.

You are missing the point. Why do you want a conditional in a hot
path? You know at init time whether the thing is BE or LE, so you can
have separate functions for BE/LE or whatever and register that with
clocksource_mmio_init(). i.e.

     if (be)
     	clocksource_mmio_init(....., cs_read_be);
     else if (le)
     	clocksource_mmio_init(....., cs_read_le);
     else if (magic)
     	clocksource_mmio_init(....., cs_read_magic);

Hmm?

	tglx
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