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Subject: Re: [PATCH v2 4/8] clk: migrate the count of orphaned clocks at
 init
From:   Marek Szyprowski <m.szyprowski@samsung.com>
To:     Jerome Brunet <jbrunet@baylibre.com>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>
Cc:     linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org,
        Stephen Boyd <sboyd@codeaurora.org>,
        Shawn Guo <shawnguo@kernel.org>,
        Dong Aisheng <aisheng.dong@nxp.com>,
        Krzysztof Kozlowski <krzk@kernel.org>
Message-id: <40e6c987-633c-b806-02e8-5299187bbcf0@samsung.com>
Date:   Mon, 05 Mar 2018 10:06:45 +0100
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References: <20180214134340.17242-1-jbrunet@baylibre.com>
        <20180214134340.17242-5-jbrunet@baylibre.com>
        <7c9b0ac1-582c-9b25-4d62-844667e80507@samsung.com>
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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