clk: fix reentrancy of clk_enable() on UP systems

Reentrant calls to clk_enable() are not working on UP systems. This is
caused by the fact spin_trylock_irqsave() always returns true when
CONFIG_SMP=n (and CONFIG_DEBUG_SPINLOCK=n) which causes the reference
counting to not work correctly when clk_enable_lock() is called twice
before clk_enable_unlock() is called (this happens when clk_enable()
is called from within another clk_enable()).

This fixes the problem by skipping the call to spin_trylock_irqsave() on UP
systems and relying solely on reference counting. We also make sure to set
flags in this case so that we are not returning an uninitialized value.

Suggested-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 647d056..b221d80 100644 (file)
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -141,10 +141,18 @@ static unsigned long clk_enable_lock(void)
 {
        unsigned long flags;
 
-       if (!spin_trylock_irqsave(&enable_lock, flags)) {
+       /*
+        * On UP systems, spin_trylock_irqsave() always returns true, even if
+        * we already hold the lock. So, in that case, we rely only on
+        * reference counting.
+        */
+       if (!IS_ENABLED(CONFIG_SMP) ||
+           !spin_trylock_irqsave(&enable_lock, flags)) {
                if (enable_owner == current) {
                        enable_refcnt++;
                        __acquire(enable_lock);
+                       if (!IS_ENABLED(CONFIG_SMP))
+                               local_save_flags(flags);
                        return flags;
                }
                spin_lock_irqsave(&enable_lock, flags);