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>

1 files changed, 9 insertions, 1 deletions

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 647d056df88c..b221d80cc7ba 100644
--- 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);