clocksource: arch_timer: Fix code to use physical timers when requested

commit 0b46b8a718c6e90910a1b1b0fe797be3c167e186 upstream.

This is a bug fix for using physical arch timers when
the arch_timer_use_virtual boolean is false.  It restores the
arch_counter_get_cntpct() function after removal in

0d651e4e "clocksource: arch_timer: use virtual counters"

We need this on certain ARMv7 systems which are architected like this:

* The firmware doesn't know and doesn't care about hypervisor mode and
  we don't want to add the complexity of hypervisor there.

* The firmware isn't involved in SMP bringup or resume.

* The ARCH timer come up with an uninitialized offset between the
  virtual and physical counters.  Each core gets a different random
  offset.

* The device boots in "Secure SVC" mode.

* Nothing has touched the reset value of CNTHCTL.PL1PCEN or
  CNTHCTL.PL1PCTEN (both default to 1 at reset)

One example of such as system is RK3288 where it is much simpler to
use the physical counter since there's nobody managing the offset and
each time a core goes down and comes back up it will get reinitialized
to some other random value.

Fixes: 0d651e4e65e9 ("clocksource: arch_timer: use virtual counters")
Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index 0704e0cf557146da78c086079daeec8c0112d326..e72aa4d802dee7299fd155b0c419fb3de45cc190 100644 (file)
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -78,6 +78,15 @@ static inline u32 arch_timer_get_cntfrq(void)
        return val;
 }
 
+static inline u64 arch_counter_get_cntpct(void)
+{
+       u64 cval;
+
+       isb();
+       asm volatile("mrrc p15, 0, %Q0, %R0, c14" : "=r" (cval));
+       return cval;
+}
+
 static inline u64 arch_counter_get_cntvct(void)
 {
        u64 cval;

diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index 9400596a0f3972a91a8858da56e9d7097e4b9319..6abb872b34d69a253141b2f9171f25fcd72df1de 100644 (file)
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -135,6 +135,15 @@ static inline void arch_timer_evtstrm_enable(int divider)
 #endif
 }
 
+static inline u64 arch_counter_get_cntpct(void)
+{
+       /*
+        * AArch64 kernel and user space mandate the use of CNTVCT.
+        */
+       BUG();
+       return 0;
+}
+
 static inline u64 arch_counter_get_cntvct(void)
 {
        u64 cval;

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index c99afdf12e9842467c0212c1f45e3c669d7b6e38..506949d2e922e130b867bcae59019d1231850594 100644 (file)
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -430,7 +430,10 @@ static void __init arch_counter_register(unsigned type)
 
        /* Register the CP15 based counter if we have one */
        if (type & ARCH_CP15_TIMER) {
-               arch_timer_read_counter = arch_counter_get_cntvct;
+               if (arch_timer_use_virtual)
+                       arch_timer_read_counter = arch_counter_get_cntvct;
+               else
+                       arch_timer_read_counter = arch_counter_get_cntpct;
        } else {
                arch_timer_read_counter = arch_counter_get_cntvct_mem;