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

Sam Protsenko
2023-12-14T16:09:54Z

On Thu, Dec 14, 2023 at 10:01 AM Tudor Ambarus <tudor.ambarus@linaro.org> wrote:
>
>
>
> On 12/14/23 15:37, Sam Protsenko wrote:
> > On Thu, Dec 14, 2023 at 4:52 AM Tudor Ambarus <tudor.ambarus@linaro.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@linaro.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
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
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
> >
> >> GATE(CLK_GOUT_CMU_PERIC1_BUS, "gout_cmu_peric1_bus",
> >> "mout_cmu_peric1_bus", CLK_CON_GAT_GATE_CLKCMU_PERIC1_BUS,
> >> 21, 0, 0),
> >> --
> >> 2.43.0.472.g3155946c3a-goog
> >>