Commit a68becd1 authored by Linus Walleij's avatar Linus Walleij Committed by Russell King
Browse files

ARM: 7563/1: SMP_TWD: make setup()/stop() reentrant

It has been brought to my knowledge that the .setup()/.stop()
function pair in the SMP TWD is going to be called from atomic
contexts for CPUs coming and going, and then the
clk_prepare()/clk_unprepare() calls cannot be called
on subsequent .setup()/.stop() iterations. This is however
just the tip of an iceberg as the function pair is not
designed to be reentrant at all.

This change makes the SMP_TWD clock .setup()/.stop() pair reentrant
by splitting the .setup() function in three parts:

- One COMMON part that is executed the first time the first CPU
  in the TWD cluster is initialized. This will fetch the TWD
  clk for the cluster and prepare+enable it. If no clk is
  available it will calibrate the rate instead.

- One part that is executed the FIRST TIME a certain CPU is
  brought on-line. This initializes and sets up the clock event
  for a certain CPU.

- One part that is executed on every subsequent .setup() call.
  This will re-initialize the clock event. This is augmented
  to call the clk_enable()/clk_disable() pair properly.

Cc: Shawn Guo <>
Reported-by: default avatarPeter Chen <>
Reviewed-by: default avatarSantosh Shilimkar <>
Tested-by: default avatarShawn Guo <>
Signed-off-by: default avatarLinus Walleij <>
Signed-off-by: default avatarRussell King <>
parent 2577cf24
......@@ -31,6 +31,8 @@ static void __iomem *twd_base;
static struct clk *twd_clk;
static unsigned long twd_timer_rate;
static bool common_setup_called;
static DEFINE_PER_CPU(bool, percpu_setup_called);
static struct clock_event_device __percpu **twd_evt;
static int twd_ppi;
......@@ -264,15 +266,45 @@ static struct clk *twd_get_clock(void)
static int __cpuinit twd_timer_setup(struct clock_event_device *clk)
struct clock_event_device **this_cpu_clk;
int cpu = smp_processor_id();
if (!twd_clk)
* If the basic setup for this CPU has been done before don't
* bother with the below.
if (per_cpu(percpu_setup_called, cpu)) {
__raw_writel(0, twd_base + TWD_TIMER_CONTROL);
enable_percpu_irq(clk->irq, 0);
return 0;
per_cpu(percpu_setup_called, cpu) = true;
* This stuff only need to be done once for the entire TWD cluster
* during the runtime of the system.
if (!common_setup_called) {
twd_clk = twd_get_clock();
if (!IS_ERR_OR_NULL(twd_clk))
twd_timer_rate = clk_get_rate(twd_clk);
* We use IS_ERR_OR_NULL() here, because if the clock stubs
* are active we will get a valid clk reference which is
* however NULL and will return the rate 0. In that case we
* need to calibrate the rate instead.
if (!IS_ERR_OR_NULL(twd_clk))
twd_timer_rate = clk_get_rate(twd_clk);
common_setup_called = true;
* The following is done once per CPU the first time .setup() is
* called.
__raw_writel(0, twd_base + TWD_TIMER_CONTROL);
clk->name = "local_timer";
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