linux-kernel - Re: [PATCH 04/11] ARM: set arch

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Date:	Fri, 09 Nov 2012 10:06:15 +1100
From:	Ryan Mallon <rmallon@...il.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	Russell King <linux@....linux.org.uk>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
	John Stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, Stephen Warren <swarren@...dia.com>,
	Andrew Victor <linux@...im.org.za>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Hartley Sweeten <hsweeten@...ionengravers.com>,
	Ben Dooks <ben-linux@...ff.org>,
	Kukjin Kim <kgene.kim@...sung.com>
Subject: Re: [PATCH 04/11] ARM: set arch_gettimeoffset directly

On 09/11/12 08:01, Stephen Warren wrote:
> From: Stephen Warren <swarren@...dia.com>
> 
> remove ARM's struct sys_timer .offset function pointer, and instead
> directly set the arch_gettimeoffset function pointer when the timer
> driver is initialized. This requires multiplying all function results
> by 1000, since the removed arm_gettimeoffset() did this. Also,
> s/unsigned long/u32/ just to make the function prototypes exactly
> match that of arch_gettimeoffset.
> 
> Cc: Russell King <linux@....linux.org.uk>
> Cc: Andrew Victor <linux@...im.org.za>
> Cc: Nicolas Ferre <nicolas.ferre@...el.com>
> Cc: Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>
> Cc: Hartley Sweeten <hsweeten@...ionengravers.com>
> Cc: Ryan Mallon <rmallon@...il.com>
> Cc: Ben Dooks <ben-linux@...ff.org>
> Cc: Kukjin Kim <kgene.kim@...sung.com>
> Signed-off-by: Stephen Warren <swarren@...dia.com>
> ---
>  arch/arm/include/asm/mach/time.h  |    3 ---
>  arch/arm/kernel/time.c            |   14 --------------
>  arch/arm/mach-at91/at91x40_time.c |    8 +++++---
>  arch/arm/mach-ebsa110/core.c      |    7 ++++---
>  arch/arm/mach-ep93xx/core.c       |   23 ++++++++++++-----------
>  arch/arm/mach-h720x/common.c      |    6 +++---
>  arch/arm/mach-h720x/common.h      |    2 +-
>  arch/arm/mach-h720x/cpu-h7201.c   |    3 ++-
>  arch/arm/mach-h720x/cpu-h7202.c   |    3 ++-
>  arch/arm/mach-rpc/time.c          |    6 +++---
>  arch/arm/plat-samsung/time.c      |    7 ++++---
>  11 files changed, 36 insertions(+), 46 deletions(-)

<snip>

> +static u32 ep93xx_gettimeoffset(void)
> +{
> +	int offset;
> +
> +	offset = __raw_readl(EP93XX_TIMER4_VALUE_LOW) - last_jiffy_time;
> +
> +	/* Calculate (1000000 / 983040) * offset.  */

This comment is now incorrect, it should say:

	/* Calculate (1000000000 / 983040) * offset */

or perhaps to better explain what is being done:

	/*
	 * Timer 4 is based on a 983.04 kHz reference clock,
	 * so dividing by 983040 gives a milli-second value.
	 * Refactor the calculation to avoid overflow.
	 */

> +	return (offset + (53 * offset / 3072)) * 1000;
> +}

~Ryan


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