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

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Message-ID: <alpine.DEB.2.10.1409041044350.3333@nanos>
Date:	Thu, 4 Sep 2014 10:45:51 +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:
> > >
> > > 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);
> > 
> 
> There already has the following access interfaces:
> 
> static inline u32 ftm_readl(void __iomem *addr)
> {
>         if (priv->big_endian)
>                 return ioread32be(addr);
>         else
>                 return ioread32(addr);
> }
> 
> static inline void ftm_writel(u32 val, void __iomem *addr)
> {
>         if (priv->big_endian)
>                 iowrite32be(val, addr);
>         else
>                 iowrite32(val, addr);
> }
> 
> So I added the following code:
> 
> static cycle_t ftm_clocksource_read_up(struct clocksource *c)
> {
>         return ftm_readl(priv->clksrc_base + FTM_CNT) & 0xffff;
> }
> 
> clocksource_mmio_init(.....,ftm_clocksource_read_up);
> 
> Is this okay ?

No. Sit down, read and try to understand what I wrote, look at your
existing code and figure out WHY it is fundamentally different to what
I told you.

Thanks,

	tglx
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