clocksource/drivers/arm_arch_timer: Drop unnecessary ISB on CVAL programming

Switching from TVAL to CVAL has a small drawback: we need an ISB
before reading the counter. We cannot get rid of it, but we can
instead remove the one that comes just after writing to CVAL.

This reduces the number of ISBs from 3 to 2 when programming
the timer.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211017124225.3018098-12-maz@kernel.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index 9f4b895..bb129b6 100644 (file)
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -31,6 +31,7 @@ void arch_timer_reg_write_cp15(int access, enum arch_timer_reg reg, u64 val)
                switch (reg) {
                case ARCH_TIMER_REG_CTRL:
                        asm volatile("mcr p15, 0, %0, c14, c2, 1" : : "r" ((u32)val));
+                       isb();
                        break;
                case ARCH_TIMER_REG_CVAL:
                        asm volatile("mcrr p15, 2, %Q0, %R0, c14" : : "r" (val));
@@ -42,6 +43,7 @@ void arch_timer_reg_write_cp15(int access, enum arch_timer_reg reg, u64 val)
                switch (reg) {
                case ARCH_TIMER_REG_CTRL:
                        asm volatile("mcr p15, 0, %0, c14, c3, 1" : : "r" ((u32)val));
+                       isb();
                        break;
                case ARCH_TIMER_REG_CVAL:
                        asm volatile("mcrr p15, 3, %Q0, %R0, c14" : : "r" (val));
@@ -52,8 +54,6 @@ void arch_timer_reg_write_cp15(int access, enum arch_timer_reg reg, u64 val)
        } else {
                BUILD_BUG();
        }
-
-       isb();
 }
 
 static __always_inline

diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index 4f4aa13..b8000ef 100644 (file)
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -95,6 +95,7 @@ void arch_timer_reg_write_cp15(int access, enum arch_timer_reg reg, u64 val)
                switch (reg) {
                case ARCH_TIMER_REG_CTRL:
                        write_sysreg(val, cntp_ctl_el0);
+                       isb();
                        break;
                case ARCH_TIMER_REG_CVAL:
                        write_sysreg(val, cntp_cval_el0);
@@ -106,6 +107,7 @@ void arch_timer_reg_write_cp15(int access, enum arch_timer_reg reg, u64 val)
                switch (reg) {
                case ARCH_TIMER_REG_CTRL:
                        write_sysreg(val, cntv_ctl_el0);
+                       isb();
                        break;
                case ARCH_TIMER_REG_CVAL:
                        write_sysreg(val, cntv_cval_el0);
@@ -116,8 +118,6 @@ void arch_timer_reg_write_cp15(int access, enum arch_timer_reg reg, u64 val)
        } else {
                BUILD_BUG();
        }
-
-       isb();
 }
 
 static __always_inline