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Date: Thu, 16 May 2024 12:43:30 +0200
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Subject: Re: [PATCH] [RFC] clk: stm32mp1: Keep RNG1 clock always running
To: Gatien CHEVALLIER <gatien.chevallier@foss.st.com>,
 linux-crypto@vger.kernel.org
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From: Marek Vasut <marex@denx.de>
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On 5/16/24 9:42 AM, Gatien CHEVALLIER wrote:

Hi,

>>>>> What if you add a trace in a random generation function in random.c?
>>>>
>>>> Do you have a function name or line number for me ?
>>>
>>> I put a trace in _get_random_bytes() in drivers/char/random.c. I'm not
>>> 100% sure but this should be the entry point when getting a random 
>>> number.
>>
>> You're right, there is a read attempt right before the hang, and 
>> __clk_is_enabled() returns 0 in stm32_read_rng() . In fact, it is the 
>> pm_runtime_get_sync() which is returning -EACCES instead of zero, and 
>> this is currently not checked so the failure is not detected before 
>> register access takes place, to register file with clock disabled, 
>> which triggers a hard hang.
>>
>> I'll be sending a patch shortly, thanks for this hint !
>>
> 
> Great news, indeed the return code isn't checked. Let's use
> pm_runtime_resume_and_get().

Yes please.

I will wonder why we get EACCES though, that basically means we are 
suspending already. Is it safe to return -errno from rng read function 
in that case ?

>>>>> After this, I'll try to reproduce the issue.
>>>>
>>>> If you have a minute to test it on some ST MP15 board, that would be 
>>>> real nice. Thanks !
>>>
>>> I tried to reproduce the issue you're facing on a STM32MP157C-DK2 no
>>> SCMI on the 6.9-rc7 kernel tag. I uses OP-TEE and TF-A in the bootchain
>>> but this should not have an impact here.
>>>
>>> How did you manage to test using "echo core > /sys/power/pm_test"?
>>> In kernel/power/suspend.c, enter_state(). If the pm_test_level is core,
>>> then an error is fired with the following trace:
>>> "Unsupported test mode for suspend to idle, please choose 
>>> none/freezer/devices/platform."
>>
>> Could this be firmware related ?
>>
>>> I've tried using "echo devices > /sys/power/pm_test" so that I can at 
>>> least test that the driver is put to sleep then wakes up. I do not
>>> reproduce your issue.
>>
>> Can you try 'processors' ?
>>
> 
> Given this:
> #ifdef CONFIG_PM_DEBUG
>          if (pm_test_level != TEST_NONE && pm_test_level <= TEST_CPUS) {
>              pr_warn("Unsupported test mode for suspend to idle

You're supposed to be suspending to 'mem' , not 'idle' . Could that be it ?