[ARM] omap: clk_set_parent: deny changing parent if clock is enabled

Richard Woodruff writes:
| The historic usage of this has been against single use leaf clocks
| (1st instance of gptimer).  When it was used it did:
|       clk_get()
|       clk_set_parent()
|       clk_enable()
|
| This usage was ok for that. Use on a disabled clock is needed.
|
| If there are multiple users on the clock or it is enabled there are
| problems.
|
| The call can still be unfriendly if 2 different drivers are using the
| clock with their own clock get/enable. It might be the function should
| return an error if usecount != 0 to stop surprises.  It is all around
| better if the parenting is done when the clock is off.

This is a good reason to ensure that the clock is not enabled when
clk_set_parent() is called.

Acked-by: Richard Woodruff <r-woodruff2@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 10 insertions, 7 deletions

diff --git a/arch/arm/plat-omap/clock.c b/arch/arm/plat-omap/clock.c
index 08baa18497b2..2e0614552ac8 100644
--- a/arch/arm/plat-omap/clock.c
+++ b/arch/arm/plat-omap/clock.c
@@ -144,13 +144,16 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
                 return ret;
 
         spin_lock_irqsave(&clockfw_lock, flags);
-        if (arch_clock->clk_set_parent)
-                ret = arch_clock->clk_set_parent(clk, parent);
-        if (ret == 0) {
-                if (clk->recalc)
-                        clk->rate = clk->recalc(clk);
-                propagate_rate(clk);
-        }
+        if (clk->usecount == 0) {
+                if (arch_clock->clk_set_parent)
+                        ret = arch_clock->clk_set_parent(clk, parent);
+                if (ret == 0) {
+                        if (clk->recalc)
+                                clk->rate = clk->recalc(clk);
+                        propagate_rate(clk);
+                }
+        } else
+                ret = -EBUSY;
         spin_unlock_irqrestore(&clockfw_lock, flags);
 
         return ret;