linux-kernel - Re: [PATCH v3 1/7] clk: introduce clk_div

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Date:	Tue, 07 Jul 2015 18:48:02 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	linux-kernel@...r.kernel.org, Sascha Hauer <kernel@...gutronix.de>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	Tero Kristo <t-kristo@...com>,
	Russell King <linux@....linux.org.uk>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>
Subject: Re: [PATCH v3 1/7] clk: introduce clk_div_mask() helper

On Thu, 2015-06-18 at 12:48 -0700, Stephen Boyd wrote:
> On 03/31, Andy Shevchenko wrote:
> > diff --git a/include/linux/clk-provider.h b/include/linux/clk
> > -provider.h
> > index 5591ea7..20b0b67 100644
> > --- a/include/linux/clk-provider.h
> > +++ b/include/linux/clk-provider.h
> > @@ -353,6 +353,11 @@ struct clk_divider {
> >  	spinlock_t	*lock;
> >  };
> >  
> > +static inline unsigned long clk_div_mask(u8 width)
> > +{
> > +	return (1 << width) - 1;
> > +}
> > +
> 
> Why not just change drivers to use GENMASK? It's a proven and
> tested way to generate a bitmask.

Too many unneeded calculations I suppose.

Compare:
	mask = clk_div_mask(mm) << ms;
	which is simple ((1 << mm) - 1) << ms
and
	mask = GENMASK(mm + ms - 1, ms);
	which is (~0 << ms) & (~0 >> (BITS_PER_LONG - 1 - (mm + ms -
1)))

> 
> So I'd rather see drivers converted to use that macro directly
> especially because the mask may need to start at some bit that
> isn't 0.

If you think the above is not a burden, I can do the conversion to
GENMASK.

Though it might make sense when ms = 0 explicitly.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy
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