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

> ---
> 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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