RE: BD71847 clk driver disables clk-32k-out causing RTC/WDT failure

[Peng Fan <peng.fan@nxp.com>]

> Subject: Re: BD71847 clk driver disables clk-32k-out causing RTC/WDT failure
> 
> On 9/9/22 04:06, Peng Fan wrote:
> >> Subject: Re: BD71847 clk driver disables clk-32k-out causing RTC/WDT
> >> failure
> >>
> >> On 9/8/22 21:25, Tim Harvey wrote:
> >>> On Thu, Sep 8, 2022 at 9:55 AM Marek Vasut <marex@denx.de> wrote:
> >>>>
> >>>> On 9/8/22 18:00, Tim Harvey wrote:
> >>>>> On Thu, Sep 1, 2022 at 9:14 PM Matti Vaittinen
> >> <mazziesaccount@gmail.com> wrote:
> >>>>>>
> >>>>>> Hi Tim,
> >>>>>>
> >>>>>> On 9/2/22 01:23, Tim Harvey wrote:
> >>>>>>> Greetings,
> >>>>>>>
> >>>>>>> I've found that the bd71847 clk driver
> >> (CONFIG_COMMON_CLK_BD718XX
> >>>>>>> drivers/clk/clk-bd718x7.c) disables clk-32k-out (the BD71847
> >>>>>>> C32K_OUT
> >>>>>>> pin) which is connected IMX8MM RTC_XTALI which ends up
> disabling
> >>>>>>> the IMX RTC as well as the IMX WDOG functionality.
> >>>>>>
> >>>>>> //snip
> >>>>>>
> >>>>>>> This happens via clk_unprepare_unused() as nothing is flagging
> >>>>>>> the clk-32k-out as being used. What should be added to the
> >>>>>>> device-tree to signify that this clk is indeed necessary and should
> not be disabled?
> >>>>>>
> >>>>>> I have seen following proposal from Marek Vasut:
> >>>>>>
> >>>>>>
> >> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fl
> >>>>>> ore.kernel.org%2Fall%2F20220517235919.200375-1-
> >> marex%40denx.de%2FT%
> >>>>>>
> >>
> 2F%23m52d6d0831bf43d5f293e35cb27f3021f278d0564&amp;data=05%7C0
> >> 1%7Cp
> >>>>>>
> >>
> eng.fan%40nxp.com%7C07d48edcc47c4694e08208da91da2bf4%7C686ea1d
> >> 3bc2b
> >>>>>>
> >>
> 4c6fa92cd99c5c301635%7C0%7C0%7C637982664162868785%7CUnknown%
> >> 7CTWFpb
> >>>>>>
> >>
> GZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI
> >> 6
> >>>>>>
> >>
> Mn0%3D%7C3000%7C%7C%7C&amp;sdata=uF26u9g4onuqCWzPRAvD%2F%
> >> 2FLByaEhh5
> >>>>>> Dtah9K8CcAOAM%3D&amp;reserved=0
> >>>>>>
> >>>>>> I am not sure if the discussion is completed though. I guess it
> >>>>>> was agreed this was needed/usefull and maybe the remaining thing
> >>>>>> to decide was just the property naming.
> >>>>>>
> >>>>>> Best Regards
> >>>>>>            -- Matti
> >>>>>>
> >>>>>
> >>>>> Thanks Matti,
> >>>>>
> >>>>> Marek - has there been any progress on determining how best to
> >>>>> keep certain clocks from being disabled?
> >>>>
> >>>> No. You can read the discussion above.
> >>>
> >>> Marek,
> >>>
> >>> I wasn't on the linux-clk list at that time so can't respond to the
> >>> thread but the discussion seems to have died out a couple of months
> >>> ago with no agreement between you or Stephen on how to deal with it.
> >>>
> >>> So where do we take this from here? It looks like there are about 18
> >>> boards with dt's using "rohm,bd718*" which would all have non
> >>> working RTC/WDOG with CONFIG_COMMON_CLK_BD718XX enabled
> (which it is
> >>> in
> >>> arch/arm64/configs/defconfig) right?
> >
> > Is there any requirement that the bd718xx clk needs to be runtime on/off?
> 
> Yes, the 32kHz clock on BD71xxx should behave like any other clock, unless
> specified otherwise, see below.
> 
> > I suppose the clk should always be never be off, if yes, why not have
> something:
> 
> What is needed in this specific case of BD718xx is I think clock consumer on
> the MX8M clock driver side which would claim the 32kHz input from the
> PMIC and up the clock enable count to keep the 32 kHz clock always on. The
> PMIC is most likely supplying 32 kHz clock to the MX8M, which if the 32 kHz
> clock are turned off would hang (I observed that before too).

i.MX8M has internal 32 KHz XTAL module, why need external pmic 32KHz feed
in?

Thanks,
Peng.
> 
> What I tried to address in this thread is a generic problem which commonly
> appears on various embedded systems, except every time anyone tried to
> solve it in a generic manner, it was rejected or they gave up.
> 
> The problem is this -- you have an arbitrary clock, and you need to keep it
> running always otherwise the system fails, and you do not have a clock
> consumer in the DT for whatever reason e.g. because the SoC is only used
> as a clock source for some unrelated clock net. There must be a way to mark
> the clock as "never disable these", i.e. critical-clock.
> (I feel like I keep repeating this over and over in this thread, so please read
> the whole thread backlog)