On 03/15/2013 11:45 AM, Russell King - ARM Linux wrote:
On Thu, Mar 14, 2013 at 02:31:04AM -0700, Bill Huang wrote:
Add the below two notifier events so drivers which are interested in knowing the clock status can act accordingly. This is extremely useful in some of the DVFS (Dynamic Voltage Frequency Scaling) design.
CLK_PREPARED CLK_UNPREPARED
Signed-off-by: Bill Huang bilhuang@nvidia.com
drivers/clk/clk.c | 3 +++ include/linux/clk.h | 2 ++ 2 files changed, 5 insertions(+)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index ed87b24..3292cec 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -550,6 +550,7 @@ void clk_unprepare(struct clk *clk) { mutex_lock(&prepare_lock); __clk_unprepare(clk);
- __clk_notify(clk, CLK_UNPREPARED, clk->rate, clk->rate); mutex_unlock(&prepare_lock);
} EXPORT_SYMBOL_GPL(clk_unprepare); @@ -598,6 +599,8 @@ int clk_prepare(struct clk *clk) mutex_lock(&prepare_lock); ret = __clk_prepare(clk);
- if (!ret)
__clk_notify(clk, CLK_PREPARED, clk->rate, clk->rate);So, on prepare, we notify after we've prepared the clock. On unprepare, we notify after the clock has been shut down. Are you sure that's the correct ordering? Would it not be better to view it in a stack-like fashion, iow:
get prepare notify-prepare enable disable notify-unprepare unprepare put
Yes, these should be stacked/nested better for consistency.
But for DVFS, the voltage needs to be raised before the prepare body is run, so that if clk_prepare actually enables the clock, the voltage is already at the safe level required by that clock. Similarly, for unprepare, you can only lower the voltage after having turned off the clock, which is guaranteed after the unprepare body. So, I think you want to move the notifier for prepare in the code above (and rename it to pre/before_prepare?), rather than the notifier for unprepare.
In order to cover more cases, you might have both {pre,post}_{un,}prepare notifiers, although I'm not sure when you'd use the other two options.
diff --git a/include/linux/clk.h b/include/linux/clk.h
+#define CLK_PREPARED BIT(3) +#define CLK_UNPREPARED BIT(4)