On 1/16/19 4:11 PM, Arnd Bergmann wrote: > On Wed, Jan 16, 2019 at 3:10 PM Fabrice Gasnier <fabrice.gasnier@xxxxxx> wrote: >> >> 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. > > What I mean is that nodes that listed as 'compatible="syscon"' get > probed by the syscon driver even when no other driver references > them, and that in turn would acquire the clock, right? Hi Arnd, Sorry for the late reply. When no other driver references them, nothing happens at probe time on the clock: no calls to get/prepare... the clock. => The clock will remain unrequested & unused until another driver calls one of "of_syscon_register()" variants: - syscon_node_to_regmap - syscon_regmap_lookup_by_compatible - syscon_regmap_lookup_by_phandle When another driver references them (e.g. one of the above calls), then it will acquire the optional clock and use it, e.g.: - clk_prepare() upon of_syscon_register() variants - clk_enable & clk_disable when accessing the registers I hope this clarifies. Please advise, Best Regards, Fabrice > >>> 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 ? > > You won't actually have two drivers binding to the same device, but you > could have a driver and a syscon user that does relies on the > syscon_regmap_lookup_by_*() functions. > > I think we've had a couple of cases where we started out representing > a device as syscon, and then later decided that a high-level abstraction > would be needed because syscon didn't quite support all the needed > features. > > Since each syscon node should also have a more specific > compatible value, you can then have another driver that binds > to that compatible string. > > Arnd >
