Message ID | 1326973942-11576-1-git-send-email-vbyravarasu@nvidia.com |
---|---|
State | Accepted |
Headers | show |
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?
> -----Original Message----- > From: Andrew Morton [mailto:akpm@linux-foundation.org] > Sent: Saturday, January 28, 2012 6:09 AM > To: Venu Byravarasu > Cc: a.zummo@towertech.it; rtc-linux@googlegroups.com; linux- > kernel@vger.kernel.org > Subject: Re: [PATCH] rtc: twl: optimize IRQ bit access > > Are these functions called frequently enough to make this optimisation > significant? I did not check how frequent these functions are called. However, as the values are cached any way, thought of using them before doing hardware access. > > I can see no locking protecting rtc_irq_bits from concurrent updaters. > Is this code as racy as it appears? Yes, looks like it is. Will push a separate patch to fix this issue.
diff --git a/drivers/rtc/rtc-twl.c b/drivers/rtc/rtc-twl.c index a0236a0..b1f6c8b 100644 --- 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)