From: Ryan Mallon <rmallon@gmail.com>
To: Stephen Warren <swarren@wwwdotorg.org>
Cc: Russell King <linux@arm.linux.org.uk>,
Olof Johansson <olof@lixom.net>, Arnd Bergmann <arnd@arndb.de>,
John Stultz <johnstul@us.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
Stephen Warren <swarren@nvidia.com>,
Andrew Victor <linux@maxim.org.za>,
Nicolas Ferre <nicolas.ferre@atmel.com>,
Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>,
Hartley Sweeten <hsweeten@visionengravers.com>,
Ben Dooks <ben-linux@fluff.org>,
Kukjin Kim <kgene.kim@samsung.com>
Subject: Re: [PATCH 04/11] ARM: set arch_gettimeoffset directly
Date: Sat, 10 Nov 2012 14:39:10 +1100 [thread overview]
Message-ID: <509DCC5E.7020804@gmail.com> (raw)
In-Reply-To: <509D708E.6080703@wwwdotorg.org>
On 10/11/12 08:07, Stephen Warren wrote:
> On 11/08/2012 04:06 PM, Ryan Mallon wrote:
>> On 09/11/12 08:01, Stephen Warren wrote:
>>> 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.
>
>>> +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;
>
> Thanks. I expanded on that slightly and went for:
>
> /*
> * Timer 4 is based on a 983.04 kHz reference clock,
> * so dividing by 983040 gives the fraction of a second,
> * so dividing by 0.983040 converts to uS.
> * Refactor the calculation to avoid overflow.
> * Finally, multiply by 1000 to give nS.
> */
>
Looks good, thanks.
~Ryan
next prev parent reply other threads:[~2012-11-10 3:38 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-08 21:01 [RFC PATCH 00/11] arch_gettimeoffset and ARM timer rework Stephen Warren
2012-11-08 21:01 ` [PATCH] ARM: delete struct sys_timer Stephen Warren
2012-11-08 21:04 ` Stephen Warren
2012-11-08 21:01 ` [PATCH 01/11] cris: move usec/nsec conversion to do_slow_gettimeoffset Stephen Warren
2012-11-12 10:44 ` Jesper Nilsson
2012-11-08 21:01 ` [PATCH 02/11] time: convert arch_gettimeoffset to a pointer Stephen Warren
2012-11-09 23:02 ` John Stultz
2012-11-11 9:45 ` Geert Uytterhoeven
2012-11-12 10:46 ` Jesper Nilsson
2012-11-08 21:01 ` [PATCH 03/11] m68k: set arch_gettimeoffset directly Stephen Warren
2012-11-11 9:50 ` Geert Uytterhoeven
2012-11-11 11:47 ` Phil Blundell
2012-11-08 21:01 ` [PATCH 04/11] ARM: " Stephen Warren
2012-11-08 23:06 ` Ryan Mallon
2012-11-09 21:07 ` Stephen Warren
2012-11-10 3:39 ` Ryan Mallon [this message]
2012-11-08 21:01 ` [PATCH 05/11] ARM: at91: convert timer suspend/resume to clock_event_device Stephen Warren
2012-11-12 14:49 ` Jean-Christophe PLAGNIOL-VILLARD
2012-11-08 21:01 ` [PATCH 06/11] ARM: pxa: " Stephen Warren
2012-11-09 2:05 ` Eric Miao
2012-11-08 21:01 ` [PATCH 07/11] ARM: sa1100: " Stephen Warren
2012-11-08 21:01 ` [PATCH 08/11] ARM: ux500: " Stephen Warren
2012-11-08 21:01 ` [PATCH 09/11] ARM: samsung: register syscore_ops for timer resume directly Stephen Warren
2012-11-08 21:01 ` [PATCH 10/11] ARM: remove struct sys_timer suspend and resume fields Stephen Warren
2012-11-08 21:01 ` [RFC PATCH 11/11] ARM: delete struct sys_timer Stephen Warren
2012-11-09 20:55 ` [PATCH V2 " Stephen Warren
2012-11-12 14:17 ` [RFC PATCH 00/11] arch_gettimeoffset and ARM timer rework Arnd Bergmann
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