On Wed, 2013-03-13 at 12:42 +0800, Stephen Warren wrote:
On 03/12/2013 07:47 PM, Bill Huang wrote:
On Tue, 2013-03-12 at 21:40 +0800, Russell King - ARM Linux wrote:
On Tue, Mar 12, 2013 at 05:37:41AM -0700, Bill Huang wrote:
Add the below four 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.
PRE_CLK_ENABLE POST_CLK_ENABLE PRE_CLK_DISABLE POST_CLK_DISABLE
Signed-off-by: Bill Huang bilhuang@nvidia.com
NAK. *Sigh* NO, this is the wrong level to be doing stuff like this.
The *ONLY* thing that clk_prepare_enable() and clk_prepare_disable() should *EVER* be doing is calling clk_prepare(), clk_enable(), clk_disable() and clk_unprepare(). Those two functions are *merely* helpers for drivers who don't wish to make the individual calls.
Drivers are still completely free to call the individual functions, at which point your proposal breaks horribly - and they _do_ call the individual functions.
I'm proposing to give device driver a choice when it knows that some driver might be interested in knowing its clock's enabled/disabled state change at runtime, this is very important for centralized DVFS core driver. It is not meant to be covering all cases especially for drivers which is not part of the DVFS, so we don't care if it is calling clk_enable/disable directly or not.
I believe the point Russell is making is not that the idea behind this patch is wrong, but simply that the function where you put the hooks is wrong. The hooks should at least be in clk_enable/clk_disable and not clk_prepare_enable/clk_disable_unprepare, since any driver is free to call clk_prepare separately from clk_enable. The hooks should be implemented in the lowest-level common function that all driver-accessible paths call through.
Thanks, I know the point, but unfortunately there is no good choice for hooking this since those low level functions clk_enable/clk_disable will be called in interrupt context so it is not possible to send notify. We might need to come out a better approach if we can think of any. Currently I still think this is acceptable (Having all the drivers which are using our interested clocks call these function to enable/disable clock in their runtime_pm calls) though it's not perfect.