linux-kernel - Re: [PATCH 07/13] clk: samsung: gs101: mark PERIC0 IP TOP gate clock as critical

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Date:   Thu, 14 Dec 2023 10:43:04 -0600
From:   Sam Protsenko <semen.protsenko@...aro.org>
To:     Tudor Ambarus <tudor.ambarus@...aro.org>
Cc:     peter.griffin@...aro.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, mturquette@...libre.com,
        sboyd@...nel.org, conor+dt@...nel.org, andi.shyti@...nel.org,
        alim.akhtar@...sung.com, gregkh@...uxfoundation.org,
        jirislaby@...nel.org, catalin.marinas@....com, will@...nel.org,
        s.nawrocki@...sung.com, tomasz.figa@...il.com,
        cw00.choi@...sung.com, arnd@...db.de, andre.draszik@...aro.org,
        saravanak@...gle.com, willmcvicker@...gle.com,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH 07/13] clk: samsung: gs101: mark PERIC0 IP TOP gate clock
 as critical

On Thu, Dec 14, 2023 at 10:15 AM Tudor Ambarus <tudor.ambarus@...aro.org> wrote:
>
>
>
> On 12/14/23 16:09, Sam Protsenko wrote:
> > On Thu, Dec 14, 2023 at 10:01 AM Tudor Ambarus <tudor.ambarus@...aro.org> wrote:
> >>
> >>
> >>
> >> On 12/14/23 15:37, Sam Protsenko wrote:
> >>> On Thu, Dec 14, 2023 at 4:52 AM Tudor Ambarus <tudor.ambarus@...aro.org> wrote:
> >>>>
> >>>> Testing USI8 I2C with an eeprom revealed that when the USI8 leaf clock
> >>>> is disabled it leads to the CMU_TOP PERIC0 IP gate clock disablement,
> >>>> which then makes the system hang. To prevent this, mark
> >>>> CLK_GOUT_CMU_PERIC0_IP as critical. Other clocks will be marked
> >>>> accordingly when tested.
> >>>>
> >>>> Signed-off-by: Tudor Ambarus <tudor.ambarus@...aro.org>
> >>>> ---
> >>>>  drivers/clk/samsung/clk-gs101.c | 2 +-
> >>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/drivers/clk/samsung/clk-gs101.c b/drivers/clk/samsung/clk-gs101.c
> >>>> index 3d194520b05e..08d80fca9cd6 100644
> >>>> --- a/drivers/clk/samsung/clk-gs101.c
> >>>> +++ b/drivers/clk/samsung/clk-gs101.c
> >>>> @@ -1402,7 +1402,7 @@ static const struct samsung_gate_clock cmu_top_gate_clks[] __initconst = {
> >>>>              "mout_cmu_peric0_bus", CLK_CON_GAT_GATE_CLKCMU_PERIC0_BUS,
> >>>>              21, 0, 0),
> >>>>         GATE(CLK_GOUT_CMU_PERIC0_IP, "gout_cmu_peric0_ip", "mout_cmu_peric0_ip",
> >>>> -            CLK_CON_GAT_GATE_CLKCMU_PERIC0_IP, 21, 0, 0),
> >>>> +            CLK_CON_GAT_GATE_CLKCMU_PERIC0_IP, 21, CLK_IS_CRITICAL, 0),
> >>>
> >>> This clock doesn't seem like a leaf clock. It's also not a bus clock.
> >>> Leaving it always running makes the whole PERIC0 CMU clocked, which
> >>> usually should be avoided. Is it possible that the system freezes
> >>> because some other clock (which depends on peric0_ip) gets disabled as
> >>> a consequence of disabling peric0_ip? Maybe it's some leaf clock which
> >>> is not implemented yet in the clock driver? Just looks weird to me
> >>> that the system hangs because of CMU IP clock disablement. It's
> >>> usually something much more specific.
> >>
> >> The system hang happened when I tested USI8 in I2C configuration with an
> >> eeprom. After the eeprom is read the leaf gate clock that gets disabled
> >> is the one on PERIC0 (CLK_GOUT_PERIC0_CLK_PERIC0_USI8_USI_CLK). I assume
> >> this leads to the CMU_TOP gate (CLK_CON_GAT_GATE_CLKCMU_PERIC0_IP)
> >> disablement which makes the system hang. Either marking the CMU_TOP gate
> >> clock as critical (as I did in this patch) or marking the leaf PERIC0
> >> gate clock as critical, gets rid of the system hang. Did I choose wrong?
> >>
> >
> > Did you already implement 100% of clocks in CMU_PERIC0? If no, there
>
> yes.

Ok. Are there any other CMUs (perhaps not implemented yet) which
consume clocks from CMU_PERIC0, specifically PERIC0_IP clock or some
clocks derived from it? If so, is there a chance some particular leaf
clock in those CMUs actually renders the system frozen when disabled
as a consequence of disabling PERIC0_IP, and would explain better why
the freeze happens?

For now I think it's ok to have that CLK_IS_CRITICAL flag here,
because as you said you implemented all clocks in this CMU and neither
of those looks like a critical one. But I'd advice to add a TODO
comment saying it's probably a temporary solution before actual leaf
clock which leads to freeze is identified (which probably resides in
some other not implemented yet CMU).

>
> > is a chance some other leaf clock (which is not implemented yet in
> > your driver) gets disabled as a result of PERIC0_IP disablement, which
> > might actually lead to that hang you observe. Usually it's some
> > meaningful leaf clock, e.g. GIC or interconnect clocks. Please check
> > clk-exynos850.c driver for CLK_IS_CRITICAL and CLK_IGNORE_UNUSED flags
> > and the corresponding comments I left there, maybe it'll give you more
> > particular idea about what to look for. Yes, making the whole CMU
> > always running without understanding why (i.e. because of which
> > particular leaf clock) might not be the best way of handling this
>
> because of CLK_GOUT_PERIC0_CLK_PERIC0_USI8_USI_CLK

That's not a root cause here. And I think PERIC0_IP is neither.

>
> > issue. I might be mistaken, but at least please check if you
> > implemented all clocks for PERIC0 first and if making some meaningful
> > leaf clock critical makes more sense.
> >
>
> Thanks,
> ta