On Wed, 2013-03-13 at 13:24 +0800, Stephen Warren wrote: > On 03/12/2013 11:08 PM, Bill Huang wrote: > > 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 <bilhu...@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. > > No, that definitely won't work. Not all drivers use those APIs, nor > should they. > That will be too bad, it looks like we deadlock in the mechanism, we cannot change existing drivers behavior (that means some call clk_disable/enable directly, some are not), and we cannot hook notifier in clk_disable/enable either, that means there seems no any chance to get what we want, any idea?
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