[3.16.y-ckt stable] Patch "clocksource: arch_timer: Fix code to use physical timers when requested" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt4.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 55b3b66e6ed349b3a28f3a5da0c373d08cae6e64 Mon Sep 17 00:00:00 2001
From: Sonny Rao <sonnyrao at chromium.org>
Date: Sun, 23 Nov 2014 23:02:44 -0800
Subject: 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 at chromium.org>
Acked-by: Catalin Marinas <catalin.marinas at arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano at linaro.org>
Signed-off-by: Olof Johansson <olof at lixom.net>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/arm/include/asm/arch_timer.h    | 9 +++++++++
 arch/arm64/include/asm/arch_timer.h  | 9 +++++++++
 drivers/clocksource/arm_arch_timer.c | 5 ++++-
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index 0704e0cf5571..e72aa4d802de 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 9400596a0f39..6abb872b34d6 100644
--- 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 c99afdf12e98..506949d2e922 100644
--- 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;

--
2.1.4