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Date: Sat, 10 Nov 2012 14:39:10 +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 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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