| Message ID | 1468952284-28942-5-git-send-email-fu.wei@linaro.org |
|---|---|
| State | New |
| Headers | show |
On Wed, Jul 20, 2016 at 02:17:59AM +0800, fu.wei@linaro.org wrote: > From: Fu Wei <fu.wei@linaro.org> > > This patch simplify arch_counter_get_cntvct_mem function by > using readq to get 64-bit CNTVCT value instead of readl_relaxed. > > Signed-off-by: Fu Wei <fu.wei@linaro.org> > --- > drivers/clocksource/arm_arch_timer.c | 10 +--------- > 1 file changed, 1 insertion(+), 9 deletions(-) > > diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c > index e6fd42d..483d2f9 100644 > --- a/drivers/clocksource/arm_arch_timer.c > +++ b/drivers/clocksource/arm_arch_timer.c > @@ -418,15 +418,7 @@ u32 arch_timer_get_rate(void) > > static u64 arch_counter_get_cntvct_mem(void) > { > - u32 vct_lo, vct_hi, tmp_hi; > - > - do { > - vct_hi = readl_relaxed(arch_counter_base + CNTVCT_HI); > - vct_lo = readl_relaxed(arch_counter_base + CNTVCT_LO); > - tmp_hi = readl_relaxed(arch_counter_base + CNTVCT_HI); > - } while (vct_hi != tmp_hi); > - > - return ((u64) vct_hi << 32) | vct_lo; > + return readq(arch_counter_base + CNTVCT_LO); What's the benefit of doing this? If you use readq here, how can we guarantee that (a) the endpoint won't generate a SLVERR or similar and (b) that we get an atomic read? "If it ain't broke, don't fix it" Will -- To unsubscribe from this list: send the line "unsubscribe linux-watchdog" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi Will, On 25 July 2016 at 17:02, Will Deacon <will.deacon@arm.com> wrote: > On Wed, Jul 20, 2016 at 02:17:59AM +0800, fu.wei@linaro.org wrote: >> From: Fu Wei <fu.wei@linaro.org> >> >> This patch simplify arch_counter_get_cntvct_mem function by >> using readq to get 64-bit CNTVCT value instead of readl_relaxed. >> >> Signed-off-by: Fu Wei <fu.wei@linaro.org> >> --- >> drivers/clocksource/arm_arch_timer.c | 10 +--------- >> 1 file changed, 1 insertion(+), 9 deletions(-) >> >> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c >> index e6fd42d..483d2f9 100644 >> --- a/drivers/clocksource/arm_arch_timer.c >> +++ b/drivers/clocksource/arm_arch_timer.c >> @@ -418,15 +418,7 @@ u32 arch_timer_get_rate(void) >> >> static u64 arch_counter_get_cntvct_mem(void) >> { >> - u32 vct_lo, vct_hi, tmp_hi; >> - >> - do { >> - vct_hi = readl_relaxed(arch_counter_base + CNTVCT_HI); >> - vct_lo = readl_relaxed(arch_counter_base + CNTVCT_LO); >> - tmp_hi = readl_relaxed(arch_counter_base + CNTVCT_HI); >> - } while (vct_hi != tmp_hi); >> - >> - return ((u64) vct_hi << 32) | vct_lo; >> + return readq(arch_counter_base + CNTVCT_LO); > Sorry, right after posting v9, I got your comment, > What's the benefit of doing this? If you use readq here, how can we benefit: 1. simplify the code 2. from arch/arm64/include/asm/io.h, I guess readq is more efficient > guarantee that (a) the endpoint won't generate a SLVERR or similar and > (b) that we get ? I think so, according to arch/arm64/include/asm/io.h. readq Implement by "LDR" and "LDAR", So I think It is an atomic read. Please correct me, If I misunderstand something, thanks > > "If it ain't broke, don't fix it" > > Will -- Best regards, Fu Wei Software Engineer Red Hat -- To unsubscribe from this list: send the line "unsubscribe linux-watchdog" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c index e6fd42d..483d2f9 100644 --- a/drivers/clocksource/arm_arch_timer.c +++ b/drivers/clocksource/arm_arch_timer.c @@ -418,15 +418,7 @@ u32 arch_timer_get_rate(void) static u64 arch_counter_get_cntvct_mem(void) { - u32 vct_lo, vct_hi, tmp_hi; - - do { - vct_hi = readl_relaxed(arch_counter_base + CNTVCT_HI); - vct_lo = readl_relaxed(arch_counter_base + CNTVCT_LO); - tmp_hi = readl_relaxed(arch_counter_base + CNTVCT_HI); - } while (vct_hi != tmp_hi); - - return ((u64) vct_hi << 32) | vct_lo; + return readq(arch_counter_base + CNTVCT_LO); } /*