Messages in this thread | | | Subject | Re: [PATCH v2 4/8] clk: migrate the count of orphaned clocks at init | From | Marek Szyprowski <> | Date | Mon, 05 Mar 2018 10:06:45 +0100 |
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Hi All,
On 2018-02-15 13:55, Marek Szyprowski wrote: > Hi Jerome, > > On 2018-02-14 14:43, Jerome Brunet wrote: >> 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@codeaurora.org> >> Cc: Shawn Guo <shawnguo@kernel.org> >> Cc: Dong Aisheng <aisheng.dong@nxp.com> >> Signed-off-by: Jerome Brunet <jbrunet@baylibre.com> > > Tested-by: Marek Szyprowski <m.szyprowski@samsung.com> > > This patch fixes kernel oops on Exynos5422-based boards (Odroid XU3/XU4) > mentioned in the following threads: > https://patchwork.kernel.org/patch/10185357/ > https://www.spinics.net/lists/linux-samsung-soc/msg61766.html
Stephen, Michael: v4.16-rc4 is out today and this regression (which got merged on 22 Dec 2017) is still not fixed yet...
Is there a chance to get it into final v4.16 release?
>> --- >> drivers/clk/clk.c | 37 +++++++++++++++++++++---------------- >> 1 file changed, 21 insertions(+), 16 deletions(-) >> >> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c >> index a4b4e4d6df5e..cca05ea2c058 100644 >> --- a/drivers/clk/clk.c >> +++ b/drivers/clk/clk.c >> @@ -2969,23 +2969,38 @@ static int __clk_core_init(struct clk_core >> *core) >> rate = 0; >> core->rate = core->req_rate = rate; >> + /* >> + * Enable CLK_IS_CRITICAL clocks so newly added critical clocks >> + * don't get accidentally disabled when walking the orphan tree and >> + * reparenting clocks >> + */ >> + if (core->flags & CLK_IS_CRITICAL) { >> + unsigned long flags; >> + >> + clk_core_prepare(core); >> + >> + flags = clk_enable_lock(); >> + clk_core_enable(core); >> + clk_enable_unlock(flags); >> + } >> + >> /* >> * walk the list of orphan clocks and reparent any that newly >> finds a >> * parent. >> */ >> hlist_for_each_entry_safe(orphan, tmp2, &clk_orphan_list, >> child_node) { >> struct clk_core *parent = __clk_init_parent(orphan); >> - unsigned long flags; >> /* >> - * we could call __clk_set_parent, but that would result in a >> - * redundant call to the .set_rate op, if it exists >> + * We need to use __clk_set_parent_before() and _after() to >> + * to properly migrate any prepare/enable count of the orphan >> + * clock. This is important for CLK_IS_CRITICAL clocks, which >> + * are enabled during init but might not have a parent yet. >> */ >> if (parent) { >> /* update the clk tree topology */ >> - flags = clk_enable_lock(); >> - clk_reparent(orphan, parent); >> - clk_enable_unlock(flags); >> + __clk_set_parent_before(orphan, parent); >> + __clk_set_parent_after(orphan, parent, NULL); >> __clk_recalc_accuracies(orphan); >> __clk_recalc_rates(orphan, 0); >> } >> @@ -3002,16 +3017,6 @@ static int __clk_core_init(struct clk_core *core) >> if (core->ops->init) >> core->ops->init(core->hw); >> - if (core->flags & CLK_IS_CRITICAL) { >> - unsigned long flags; >> - >> - clk_core_prepare(core); >> - >> - flags = clk_enable_lock(); >> - clk_core_enable(core); >> - clk_enable_unlock(flags); >> - } >> - >> kref_init(&core->ref); >> out: >> clk_pm_runtime_put(core); >
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
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