Messages in this thread | | | Date | Fri, 27 Jan 2012 16:38:40 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] rtc: twl: optimize IRQ bit access |
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On Thu, 19 Jan 2012 17:22:22 +0530 Venu Byravarasu <vbyravarasu@nvidia.com> wrote:
> From: Venu Byravarasu <vbyravarasu@nvidia.com> > > As TWL RTC driver is having a cached copy of enabled RTC interrupt bits > in variable rtc_irq_bits, that can be checked before really setting > or masking any of the interrupt bits. > > ... > > --- a/drivers/rtc/rtc-twl.c > +++ b/drivers/rtc/rtc-twl.c > @@ -176,6 +176,10 @@ static int set_rtc_irq_bit(unsigned char bit) > unsigned char val; > int ret; > > + /* if the bit is set, return from here */ > + if (rtc_irq_bits & bit) > + return 0; > + > val = rtc_irq_bits | bit; > val &= ~BIT_RTC_INTERRUPTS_REG_EVERY_M; > ret = twl_rtc_write_u8(val, REG_RTC_INTERRUPTS_REG); > @@ -193,6 +197,10 @@ static int mask_rtc_irq_bit(unsigned char bit) > unsigned char val; > int ret; > > + /* if the bit is clear, return from here */ > + if (!(rtc_irq_bits & bit)) > + return 0; > + > val = rtc_irq_bits & ~bit; > ret = twl_rtc_write_u8(val, REG_RTC_INTERRUPTS_REG); > if (ret == 0)
Are these functions called frequently enough to make this optimisation significant?
I can see no locking protecting rtc_irq_bits from concurrent updaters. Is this code as racy as it appears?
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