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Date: Thu, 16 May 2024 03:06:35 +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
Cc: =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>,
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 Stephen Boyd <sboyd@kernel.org>, Yang Yingliang <yangyingliang@huawei.com>,
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From: Marek Vasut <marex@denx.de>
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On 5/15/24 11:16 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 !

>>> 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' ?

I did also notice it sometimes takes much longer than a minute to hang, 
but eventually it does hang. Maybe let it cycle for an hour or a few ?

[...]

-- 
Best regards,
Marek Vasut