linux-kernel - [PATCH v4] clocksource: arch_timer: Fix code to use physical timers when requested

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Date:	Wed,  8 Oct 2014 00:38:57 -0700
From:	Sonny Rao <sonnyrao@...omium.org>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	linux-kernel@...r.kernel.org, dianders@...omium.org,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>,
	Olof Johansson <olof@...om.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King <linux@....linux.org.uk>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Sonny Rao <sonnyrao@...omium.org>, stable@...r.kernel.org
Subject: [PATCH v4] clocksource: arch_timer: Fix code to use physical timers when requested

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")
Cc: stable@...r.kernel.org
Signed-off-by: Sonny Rao <sonnyrao@...omium.org>
Acked-by: Olof Johansson <olof@...om.net>
---
v2: Add fixes tag to commit message, cc stable, copy Doug's
    description of the systems which need this in commit message.
v3: Don't change the memory-mapped physical timer/counter code
v4: remove the memory-mapped physical counter code since it's not used
---
 arch/arm/include/asm/arch_timer.h    |  9 +++++++++
 arch/arm64/include/asm/arch_timer.h  | 10 ++++++++++
 drivers/clocksource/arm_arch_timer.c | 10 +++++++---
 3 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index 0704e0c..e72aa4d 100644
--- 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 9400596..58657c4 100644
--- a/arch/arm64/include/asm/arch_timer.h
+++ b/arch/arm64/include/asm/arch_timer.h
@@ -135,6 +135,16 @@ static inline void arch_timer_evtstrm_enable(int divider)
 #endif
 }
 
+static inline u64 arch_counter_get_cntpct(void)
+{
+	u64 cval;
+
+	isb();
+	asm volatile("mrs %0, cntpct_el0" : "=r" (cval));
+
+	return cval;
+}
+
 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 6b50311..799139f 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -429,10 +429,14 @@ static void __init arch_counter_register(unsigned type)
 	u64 start_count;
 
 	/* Register the CP15 based counter if we have one */
-	if (type & ARCH_CP15_TIMER)
-		arch_timer_read_counter = arch_counter_get_cntvct;
-	else
+	if (type & ARCH_CP15_TIMER) {
+		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;
+	}
 
 	start_count = arch_timer_read_counter();
 	clocksource_register_hz(&clocksource_counter, arch_timer_rate);
-- 
1.8.3.2

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