On 1/28/19 2:20 PM, Fabrice Gasnier wrote: > 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 Hi Arnd, Gentlemen reminder for this. I would appreciate to have your feedback. Many thanks, 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 >>
