On Mon, 03 Jul 2017, Dirk Behme wrote:
> On 03.07.2017 16:25, Lee Jones wrote:
> > On Mon, 03 Jul 2017, Dirk Behme wrote:
> >
> > > On 03.07.2017 13:53, Lee Jones wrote:
> > > > On Tue, 27 Jun 2017, Dirk Behme wrote:
> > > >
> > > > > On 11.02.2016 01:43, Michael Turquette wrote:
> > > > > > Quoting Lee Jones (2016-01-18 06:28:50)
> > > > > > > Signed-off-by: Lee Jones <lee.jo...@linaro.org>
> > > > > >
> > > > > > Looks good to me.
> > > > > >
> > > > > > Regards,
> > > > > > Mike
> > > > > >
> > > > > > > ---
> > > > > > > drivers/clk/clk.c | 6 ++++++
> > > > > > > 1 file changed, 6 insertions(+)
> > > > > > >
> > > > > > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > > > > > > index 835cb85..178b364 100644
> > > > > > > --- a/drivers/clk/clk.c
> > > > > > > +++ b/drivers/clk/clk.c
> > > > > > > @@ -575,6 +575,9 @@ static void clk_core_unprepare(struct
> > > > > > > clk_core *core)
> > > > > > > if (WARN_ON(core->prepare_count == 0))
> > > > > > > return;
> > > > > > > + if (WARN_ON(core->prepare_count == 1 && core->flags &
> > > > > > > CLK_IS_CRITICAL))
> > > > > > > + return;
> > > > > > > +
> > > > > > > if (--core->prepare_count > 0)
> > > > > > > return;
> > > > > > > @@ -680,6 +683,9 @@ static void clk_core_disable(struct clk_core
> > > > > > > *core)
> > > > > > > if (WARN_ON(core->enable_count == 0))
> > > > > > > return;
> > > > > > > + if (WARN_ON(core->enable_count == 1 && core->flags &
> > > > > > > CLK_IS_CRITICAL))
> > > > > > > + return;
> > > > > > > +
> > > > > > > if (--core->enable_count > 0)
> > > > > > > return;
> > > > >
> > > > >
> > > > > I have a question regarding this patch, which is mainline meanwhile
> > > > > [1]:
> > > > >
> > > > > Having the following clock configuration:
> > > > >
> > > > > |--> child clk '1' (crit)
> > > > > clk source --> parent clk 'A' (crit) -->|
> > > > > |--> child clk '2'
> > > > >
> > > > >
> > > > > Clock '2' might be used, or not. It might be disabled or not. It
> > > > > doesn't
> > > > > matter. Clock '1' is not allowed to be disabled. Therefore its marked
> > > > > as
> > > > > critical.
> > > > >
> > > > > Parent clock 'A' is marked as critical because its not allowed to be
> > > > > disabled, even if the enable_count of all child clocks is 0. To avoid
> > > > > that
> > > > > by disabling parent clock 'A' the child clock '1' is disabled, too,
> > > > > whats
> > > > > not allowed as its marked as critical.
> > > > >
> > > > >
> > > > > Now, child clock '2' is used and enabled & disabled continuously by a
> > > > > (SPI)
> > > > > driver. What is ok. But:
> > > > >
> > > > > Disabling child clock '2' results in the attempt to disable parent
> > > > > clock
> > > > > 'A', too, which has correct enable_count 1 (from enabling the child
> > > > > '2').
> > > > > What results
> > > > >
> > > > > a) in the WARN_ON output
> > > > >
> > > > > and
> > > > >
> > > > > b) enable_count of 'A' never decreases to 0. Being off by one after
> > > > > the
> > > > > WARN_ON
> > > > >
> > > > >
> > > > > It sounds like both is wrong for a configuration like above.
> > > >
> > > > Clock A still has one user, Clock 1.
> > > >
> > > > Why is that wrong?
> > >
> > >
> > > Because clock 1 is not a (Linux kernel clock framework) used clock. Its
> > > enable count is 0. So from Linux kernel (clock framework) point of view
> > > clock 1 is unused.
> >
> > All critical clocks are 'used'. That's the point of critical clocks.
>
> Could you translate 'used' to enable_count? Whats valid enable_count numbers
> for critical clocks?
'used' == 'currently in use' == 'enabled'
Here's the piece of the puzzle you're probably missing:
if (core->flags & CLK_IS_CRITICAL) {
clk_core_prepare(core);
clk_core_enable(core);
}
Any clock that is identified as critical is prepared and enabled.
Thus your use_count of 1 is actually correct.
> > > The increase/decrease of enable count of parent clock A is only driven by
> > > the Linux kernel usage of clock 2.
> > >
> > > > > Opinions or proposal how to fix/change this?
> > > > >
> > > > >
> > > > > Best regards
> > > > >
> > > > > Dirk
> > > > >
> > > > > [1]
> > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/clk/clk.c?id=2e20fbf592621b2c2aeddd82e0fa3dad053cce03
> >
>
--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
