Re: [PATCH v2 4/8] clk: migrate the count of orphaned clocks at init

[Michael Turquette]

Excerpts from Heiko StÃbner's message of February 15, 2018 1:01 pm:
> Am Mittwoch, 14. Februar 2018, 14:43:36 CET schrieb Jerome Brunet:
> > The orphan clocks reparents should migrate any existing count from the
> > orphan clock to its new acestor clocks, otherwise we may have
> > inconsistent counts in the tree and end-up with gated critical clocks
> >
> > Assuming we have two clocks, A and B.
> > * Clock A has CLK_IS_CRITICAL flag set.
> > * Clock B is an ancestor of A which can gate. Clock B gate is left
> >   enabled by the bootloader.
> >
> > Step 1: Clock A is registered. Since it is a critical clock, it is
> > enabled. The clock being still an orphan, no parent are enabled.
> >
> > Step 2: Clock B is registered and reparented to clock A (potentially
> > through several other clocks). We are now in situation where the enable
> > count of clock A is 1 while the enable count of its ancestors is 0, which
> > is not good.
> >
> > Step 3: in lateinit, clk_disable_unused() is called, the enable_count of
> > clock B being 0, clock B is gated and and critical clock A actually gets
> > disabled.
> >
> > This situation was found while adding fdiv_clk gates to the meson8b
> > platform.  These clocks parent clk81 critical clock, which is the mother
> > of all peripheral clocks in this system. Because of the issue described
> > here, the system is crashing when clk_disable_unused() is called.
> >
> > The situation is solved by reverting
> > commit f8f8f1d04494 ("clk: Don't touch hardware when reparenting during
> > registration"). To avoid breaking again the situation described in this
> > commit
> > description, enabling critical clock should be done before walking the
> > orphan list. This way, a parent critical clock may not be accidentally
> > disabled due to the CLK_OPS_PARENT_ENABLE mechanism.
> >
> > Fixes: f8f8f1d04494 ("clk: Don't touch hardware when reparenting during
> > registration") Cc: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> > Cc: Shawn Guo <shawnguo@xxxxxxxxxx>
> > Cc: Dong Aisheng <aisheng.dong@xxxxxxx>
> > Signed-off-by: Jerome Brunet <jbrunet@xxxxxxxxxxxx>
>
> On a rk3288-veyron Chromebook
> Tested-by: Heiko Stuebner <heiko@xxxxxxxxx>
>
> This made the hdmi on the machine work again with 4.16-rc1 .
> (hdmi-cec clock is sourced from the i2c connected pmic which provides
> the 32kHz clock needed)
>
> So it would be really cool if this could make it into 4.16-rc :-)

I separated this patch out into clk-fixes to be set for -rc5 or -rc6.

Regards,
Mike

> Heiko