4.9-stable review patch. If anyone has any objections, please let me know.
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From: Jerome Brunet jbrunet@baylibre.com
commit 99652a469df19086d594e8e89757d4081a812789 upstream.
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 Tested-by: Heiko Stuebner heiko@sntech.de Signed-off-by: Michael Turquette mturquette@baylibre.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/clk/clk.c | 37 +++++++++++++++++++++---------------- 1 file changed, 21 insertions(+), 16 deletions(-)
--- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -2438,22 +2438,37 @@ static int __clk_core_init(struct clk_co 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); } @@ -2470,16 +2485,6 @@ static int __clk_core_init(struct clk_co 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_prepare_unlock();