linux-kernel - RE: [PATCH net-next 1/7] timecounter: provide a macro to initialize the cyclecounter mask field.

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Date:	Mon, 5 Jan 2015 13:20:57 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Richard Cochran' <richardcochran@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"David Miller" <davem@...emloft.net>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: RE: [PATCH net-next 1/7] timecounter: provide a macro to initialize
 the cyclecounter mask field.

> There is no need for users of the timecounter/cyclecounter code to include
> clocksource.h just for a single macro.
> 
> Signed-off-by: Richard Cochran <richardcochran@...il.com>
> ---
>  include/linux/timecounter.h |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/timecounter.h b/include/linux/timecounter.h
> index 74f4549..4382035 100644
> --- a/include/linux/timecounter.h
> +++ b/include/linux/timecounter.h
> @@ -19,6 +19,9 @@
> 
>  #include <linux/types.h>
> 
> +/* simplify initialization of mask field */
> +#define CYCLECOUNTER_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)

That has me chasing through the C integer promotion rules.
Better might be:
	((bits) < 64 ? (1ULL << (bits)) - 1 : (((1ULL << 63) - 1) << 1) + 1)
I actually suspect there is a standard definition somewhere?

	David 
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