[PATCH] clk: Properly update prepare/enable count on orphan clock reparent

Fri Jan 26 01:14:32 PST 2018

Hi Aisheng and Stephen,

On 2018-01-26 10:06, Marek Szyprowski wrote:
> Hi Aisheng,
>
> On 2018-01-26 09:36, A.s. Dong wrote:
>>> -----Original Message-----
>>> From: Marek Szyprowski [mailto:m.szyprowski at samsung.com]
>>> Sent: Friday, January 26, 2018 3:31 PM
>>> To: Stephen Boyd <sboyd at codeaurora.org>
>>> Cc: linux-clk at vger.kernel.org; linux-arm-kernel at lists.infradead.org; 
>>> Michael
>>> Turquette <mturquette at baylibre.com>; Shawn Guo <shawnguo at kernel.org>;
>>> A.s. Dong <aisheng.dong at nxp.com>; Bartlomiej Zolnierkiewicz
>>> <b.zolnierkie at samsung.com>
>>> Subject: Re: [PATCH] clk: Properly update prepare/enable count on 
>>> orphan
>>> clock reparent
>>>
>>> Hi Stephen,
>>>
>>> On 2018-01-25 23:19, Stephen Boyd wrote:
>>>> On 01/15, Marek Szyprowski wrote:
>>>>> If orphaned clock has been already prepared/enabled (for example if
>>>>> it or one of its children has CLK_IS_CRITICAL flag), then the
>>>>> prepare/enable counters of the newly assigned parent are not updated
>>>>> correctly. This might later cause warnings during changing clock 
>>>>> parents.
>>>>>
>>>>> This patch fixes following warning on Exynos5422-based boards:
>>>>> ------------[ cut here ]------------
>>>>> WARNING: CPU: 0 PID: 59 at drivers/clk/clk.c:811
>>>>> clk_core_disable_lock+0x18/0x24 Modules linked in:
>>>>> CPU: 0 PID: 59 Comm: kworker/0:1 Not tainted 4.15.0-rc7-next-20180115
>>>>> #106 Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
>>>>> Workqueue: pm genpd_power_off_work_fn [<c0111504>]
>>> (unwind_backtrace)
>>>>> from [<c010dbec>] (show_stack+0x10/0x14) [<c010dbec>] (show_stack)
>>>>> from [<c09b3f34>] (dump_stack+0x90/0xc8) [<c09b3f34>] (dump_stack)
>>>>> from [<c0125060>] (__warn+0xe4/0x110) [<c0125060>] (__warn) from
>>>>> [<c01250cc>] (warn_slowpath_null+0x40/0x48) [<c01250cc>]
>>>>> (warn_slowpath_null) from [<c048d584>]
>>>>> (clk_core_disable_lock+0x18/0x24) [<c048d584>]
>>>>> (clk_core_disable_lock) from [<c048e490>]
>>>>> (clk_core_disable_unprepare+0xc/0x20)
>>>>> [<c048e490>] (clk_core_disable_unprepare) from [<c048ea60>]
>>>>> (__clk_set_parent_after+0x48/0x4c)
>>>>> [<c048ea60>] (__clk_set_parent_after) from [<c048ec88>]
>>>>> (clk_core_set_parent_nolock+0x224/0x5b4)
>>>>> [<c048ec88>] (clk_core_set_parent_nolock) from [<c048f23c>]
>>>>> (clk_set_parent+0x38/0x6c) [<c048f23c>] (clk_set_parent) from
>>>>> [<c049c41c>] (exynos_pd_power+0x74/0x1cc) [<c049c41c>]
>>>>> (exynos_pd_power) from [<c0550768>] (genpd_power_off+0x164/0x264)
>>>>> [<c0550768>] (genpd_power_off) from [<c0550b34>]
>>>>> (genpd_power_off_work_fn+0x2c/0x40)
>>>>> [<c0550b34>] (genpd_power_off_work_fn) from [<c01432e4>]
>>>>> (process_one_work+0x1d0/0x7bc) [<c01432e4>] (process_one_work) from
>>>>> [<c014393c>] (worker_thread+0x34/0x4dc) [<c014393c>] (worker_thread)
>>>>> from [<c014a0d0>] (kthread+0x128/0x164) [<c014a0d0>] (kthread) from
>>>>> [<c01010b4>] (ret_from_fork+0x14/0x20) Exception stack(0xeeb01fb0 to
>>> 0xeeb01ff8)
>>>>> 1fa0: 00000000 00000000 00000000 00000000
>>>>> 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>>>>> 00000000
>>>>> 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000 ---[ end
>>>>> trace 503c239fb760f17a ]--- ------------[ cut here ]------------
>>>>> WARNING: CPU: 0 PID: 59 at drivers/clk/clk.c:684
>>>>> clk_core_disable_unprepare+0x18/0x20
>>>>> Modules linked in:
>>>>> CPU: 0 PID: 59 Comm: kworker/0:1 Tainted: G W        4.15.0-rc7-next-
>>> 20180115 #106
>>>>> Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
>>>>> Workqueue: pm genpd_power_off_work_fn [<c0111504>]
>>> (unwind_backtrace)
>>>>> from [<c010dbec>] (show_stack+0x10/0x14) [<c010dbec>] (show_stack)
>>>>> from [<c09b3f34>] (dump_stack+0x90/0xc8) [<c09b3f34>] (dump_stack)
>>>>> from [<c0125060>] (__warn+0xe4/0x110) [<c0125060>] (__warn) from
>>>>> [<c01250cc>] (warn_slowpath_null+0x40/0x48) [<c01250cc>]
>>>>> (warn_slowpath_null) from [<c048e49c>]
>>>>> (clk_core_disable_unprepare+0x18/0x20)
>>>>> [<c048e49c>] (clk_core_disable_unprepare) from [<c048ea60>]
>>>>> (__clk_set_parent_after+0x48/0x4c)
>>>>> [<c048ea60>] (__clk_set_parent_after) from [<c048ec88>]
>>>>> (clk_core_set_parent_nolock+0x224/0x5b4)
>>>>> [<c048ec88>] (clk_core_set_parent_nolock) from [<c048f23c>]
>>>>> (clk_set_parent+0x38/0x6c) [<c048f23c>] (clk_set_parent) from
>>>>> [<c049c41c>] (exynos_pd_power+0x74/0x1cc) [<c049c41c>]
>>>>> (exynos_pd_power) from [<c0550768>] (genpd_power_off+0x164/0x264)
>>>>> [<c0550768>] (genpd_power_off) from [<c0550b34>]
>>>>> (genpd_power_off_work_fn+0x2c/0x40)
>>>>> [<c0550b34>] (genpd_power_off_work_fn) from [<c01432e4>]
>>>>> (process_one_work+0x1d0/0x7bc) [<c01432e4>] (process_one_work) from
>>>>> [<c014393c>] (worker_thread+0x34/0x4dc) [<c014393c>] (worker_thread)
>>>>> from [<c014a0d0>] (kthread+0x128/0x164) [<c014a0d0>] (kthread) from
>>>>> [<c01010b4>] (ret_from_fork+0x14/0x20) Exception stack(0xeeb01fb0 to
>>> 0xeeb01ff8)
>>>>> 1fa0: 00000000 00000000 00000000 00000000
>>>>> 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>>>>> 00000000
>>>>> 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000 ---[ end
>>>>> trace 503c239fb760f17b ]--- ------------[ cut here ]------------
>>>>>
>>>>> Fixes: f8f8f1d04494 ("clk: Don't touch hardware when reparenting
>>>>> during registration")
>>>>> Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
>>>>> ---
>>>>>    drivers/clk/clk.c | 4 ++++
>>>>>    1 file changed, 4 insertions(+)
>>>>>
>>>>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index
>>>>> 0f686a9dac3e..d33c087d7868 100644
>>>>> --- a/drivers/clk/clk.c
>>>>> +++ b/drivers/clk/clk.c
>>>>> @@ -2982,6 +2982,10 @@ static int __clk_core_init(struct clk_core 
>>>>> *core)
>>>>>            if (parent) {
>>>>>                /* update the clk tree topology */
>>>>>                flags = clk_enable_lock();
>>>> This is the spinlock?
>>> yes
>>>
>>>>> +            if (orphan->prepare_count)
>>>>> +                clk_core_prepare(parent);
>>>> And this is prepare mutex? Doesn't sound like it will work.
>>> Prepare mutex is taken at the beginning of __clk_core_init() 
>>> function, so
>>> everything is fine here.
>>>
>> Theoretically no issue may happen, just looks strange to claim mutex 
>> within
>> spinlock.
>
> Nope, the mutex is taken before entering this block of code. What is 
> strange
> then? clk_core_prepare() doesn't touch prepare mutex, there is also
> a clk_core_prepare_lock() function, which takes it.

Okay, I got your concerns. To make this part a bit easier to understand, 
I will
move "if (orphan->prepare_count) clk_core_prepare(parent);" to be called 
before
"flags = clk_enable_lock();".

>>>>> +            if (orphan->enable_count)
>>>>> +                clk_core_enable(parent);
>>>> This would be OK, but then we might touch the hardware again?
>>> Well, it will touch hardware in one case: if orphaned clock is 
>>> already prepared
>>> and enabled (for example due to having CLK_IS_CRITICAL flag) and the 
>>> newly
>>> registered parent is not (yet?) enabled. Then it will prepare and 
>>> enable this
>>> new parent clock, what is a desired behavior.
>>>
>>> This code will not temporarily disable any clocks, what I assume was 
>>> the main
>>> reason for the patch mentioned in the commit message.
>>>
>> Then this code seems bypass the CLK_OPS_PARENT_ENABLE feature.
>
> Well, CLK_OPS_PARENT_ENABLE doesn't affect preparing/enabling parent 
> clock if
> child clock has been already prepared/enabled. That's all that this 
> fix do, so
> I don't know what do you mean by bypassing the CLK_OPS_PARENT_ENABLE 
> feature.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland