On 1/16/19 1:14 PM, Arnd Bergmann wrote: > (sorry for the late reply, I just realized that I had never sent out the > mail after Lee asked me for a review last year and I had drafted > my reply). Hi Arnd, Many thanks for reviewing, no worries :-) > > On Wed, Dec 12, 2018 at 9:48 AM Fabrice Gasnier <fabrice.gasnier@xxxxxx> wrote: >> >> Some system control registers need to be clocked, so the registers can >> be accessed. Add an optional clock and attach it to regmap. >> >> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxx> > > This looks ok to me in principle, but I have one question: When we > do a clk_get() and clk_prepare() as part of regmap_mmio_attach_clk(), > does that change the behavior of syscon nodes that are otherwise > unused? I'm not sure I correctly understand this question. I don't think it will change the behavior for "unused" nodes. These should remain unused with this patch. > > I think we have a bunch of devices that started out as a syscon but > then we added a proper driver for them, which would handle the > clocks explicitly. Is it guaranteed that this will keep working (including > shutting down the clocks when they are unused) if we have two drivers > that call clk_get() on the same device node? I'd expect nothing wrong happens when two drivers call clk_get() for the same clock. Are there some case where two drivers are bind (e.g. syscon driver + another driver) for the same piece of hardware ? The clk_prepare() is part of regmap_mmio_attach_clk(). It's called once upon registration via of_syscon_register(). There is currently no mean to unregister, e.g. something like "of_syscon_unregister" and so do clk_unprepare via regmap_mmio_detach_clk(). Then point is clk_enable()/clk_disable() calls will be used in regmap_mmio_read() and regmap_mmio_write(). These calls are balanced. Then clock framework should correctly disable/gate the clock when unused, based on the enable count. Is this answering your question? Thanks again, Best regards, Fabrice > > Arnd >
