* [PATCH] rtc: twl: optimize IRQ bit access
@ 2012-01-19 11:52 Venu Byravarasu
2012-01-28 0:38 ` Andrew Morton
0 siblings, 1 reply; 3+ messages in thread
From: Venu Byravarasu @ 2012-01-19 11:52 UTC (permalink / raw)
To: a.zummo, rtc-linux, linux-kernel; +Cc: Venu Byravarasu
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.
Signed-off-by: Venu Byravarasu <vbyravarasu@nvidia.com>
---
drivers/rtc/rtc-twl.c | 8 ++++++++
1 files changed, 8 insertions(+), 0 deletions(-)
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)
--
1.7.1.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] rtc: twl: optimize IRQ bit access
2012-01-19 11:52 [PATCH] rtc: twl: optimize IRQ bit access Venu Byravarasu
@ 2012-01-28 0:38 ` Andrew Morton
2012-01-30 3:17 ` Venu Byravarasu
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2012-01-28 0:38 UTC (permalink / raw)
To: Venu Byravarasu; +Cc: a.zummo, rtc-linux, linux-kernel
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?
^ permalink raw reply [flat|nested] 3+ messages in thread
* RE: [PATCH] rtc: twl: optimize IRQ bit access
2012-01-28 0:38 ` Andrew Morton
@ 2012-01-30 3:17 ` Venu Byravarasu
0 siblings, 0 replies; 3+ messages in thread
From: Venu Byravarasu @ 2012-01-30 3:17 UTC (permalink / raw)
To: Andrew Morton; +Cc: a.zummo, rtc-linux, linux-kernel
> -----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.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2012-01-19 11:52 [PATCH] rtc: twl: optimize IRQ bit access Venu Byravarasu
2012-01-28 0:38 ` Andrew Morton
2012-01-30 3:17 ` Venu Byravarasu
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