Re: [PATCH RESEND v3 1/4] clk: imx: imx8mq: fix a53 cpu clock

[Leonard Crestez <leonard.crestez@nxp.com>]

On 2020-03-11 3:16 AM, Peng Fan wrote:
>> Subject: Re: [PATCH RESEND v3 1/4] clk: imx: imx8mq: fix a53 cpu clock
>>
>> On 19.02.2020 12:23, Peng Fan wrote:
>>> From: Peng Fan <peng.fan@nxp.com>
>>>
>>> The A53 CCM clk root only accepts input up to 1GHz, CCM A53 root
>>> signoff timing is 1Ghz, however the A53 core which sources from CCM
>>> root could run above 1GHz which violates the CCM.
>>>
>>> There is a CORE_SEL slice before A53 core, we need to configure the
>>> CORE_SEL slice source from ARM PLL, not A53 CCM clk root.
>>>
>>> The A53 CCM clk root should only be used when need to change ARM PLL
>>> frequency.
>>>
>>> Add arm_a53_core clk that could source from arm_a53_div and
>> arm_pll_out.
>>> Configure a53 ccm root sources from 800MHz sys pll Configure a53 core
>>> sources from arm_pll_out Mark arm_a53_core as critical clock
>>>
>>> +	clk_hw_set_parent(hws[IMX8MQ_CLK_A53_SRC],
>> hws[IMX8MQ_SYS1_PLL_800M]);
>>> +	clk_hw_set_parent(hws[IMX8MQ_CLK_A53_CORE],
>>> +hws[IMX8MQ_ARM_PLL_OUT]);
>>
>> This triggers lockdep warnings:
>>
>> [    2.041743] ------------[ cut here ]------------
>>
>> [    2.043531] WARNING: CPU: 2 PID: 1 at drivers/clk/clk.c:2480
>> clk_core_set_parent_nolock+0x1d4/0x508
>> [    2.052584] Modules linked in:
>>
>> [    2.055642] CPU: 2 PID: 1 Comm: swapper/0 Not tainted
>> 5.6.0-rc4-next-20200306-00027-g6b7e51d87f22 #225
>> [    2.064966] Hardware name: NXP i.MX8MQ EVK (DT)
>>
>> [    2.069504] pstate: 60000005 (nZCv daif -PAN -UAO)
>>
>> [    2.074298] pc : clk_core_set_parent_nolock+0x1d4/0x508
>>
>> [    2.079529] lr : clk_core_set_parent_nolock+0x1d0/0x508
>>
>>
>> [    2.084759] sp : ffff80001003b9b0
>>
>>
>> [    2.088072] x29: ffff80001003b9b0 x28: ffff8000116e8218
>>
>>
>> [    2.093392] x27: 0000000000004570 x26: ffff8000128745d0
>>
>>
>> [    2.098711] x25: ffff0000b8422008 x24: ffff0000b8422008
>>
>> [    2.104030] x23: ffff80001104a518 x22: ffff80001104a508
>>
>> [    2.109349] x21: ffff800012260bf8 x20: ffff0000b84c9600
>>
>> [    2.114668] x19: ffff0000b84cbb00 x18: 0000000000004530
>>
>> [    2.119987] x17: 0000000000004520 x16: 0000000000004510
>>
>>
>> [    2.125307] x15: 00000000000045d0 x14: 0000000000004500
>>
>>
>> [    2.130626] x13: 00000000000044f0 x12: 00000000000044e0
>>
>> [    2.135945] x11: ffff8000116e6c68 x10: ffff8000117d7000
>>
>>
>> [    2.141264] x9 : ffff80001067007c x8 : 0000000000000000
>>
>> [    2.146583] x7 : ffff800010671938 x6 : 0000000000000000
>>
>>
>> [    2.151903] x5 : ffff800011633000 x4 : 0000000000000000
>>
>> [    2.157222] x3 : ffff80001003b804 x2 : 0000000000000000
>>
>>
>> [    2.162541] x1 : ffff0000b9da0000 x0 : 0000000000000000
>>
>> [    2.167862] Call trace:
>>
>> [    2.170307]  clk_core_set_parent_nolock+0x1d4/0x508
>>
>> [    2.175190]  clk_hw_set_parent+0x1c/0x28
>>
>> [    2.179114]  imx8mq_clocks_probe+0x3538/0x3668
>>
>> [    2.183562]  platform_drv_probe+0x58/0xa8
>>
>> [    2.187573]  really_probe+0xe0/0x440
>>
>>
>> [    2.191145]  driver_probe_device+0xe4/0x138
>> [    2.195333]  device_driver_attach+0x74/0x80
>>
>>
>> [    2.199519]  __driver_attach+0xa8/0x170
>>
>> [    2.203354]  bus_for_each_dev+0x74/0xc8
>>
>>
>> [    2.207190]  driver_attach+0x28/0x30
>>
>> [    2.210767]  bus_add_driver+0x144/0x228
>>
>>
>> [    2.214605]  driver_register+0x68/0x118
>>
>> [    2.218438]  __platform_driver_register+0x4c/0x58
>>
>>
>> [    2.223151]  imx8mq_clk_driver_init+0x20/0x28
>>
>> [    2.227511]  do_one_initcall+0x88/0x410
>>
>> [    2.231348]  kernel_init_freeable+0x24c/0x2c0
>>
>> [    2.235706]  kernel_init+0x18/0x108
>>
>> [    2.239192]  ret_from_fork+0x10/0x18
>>
>> [    2.242768] irq event stamp: 130084
>>
>> [    2.246262] hardirqs last  enabled at (130083): [<ffff800010302e78>]
>> __slab_alloc.isra.0+0x90/0xb8
>> [    2.255241] hardirqs last disabled at (130084): [<ffff8000100a60b0>]
>> do_debug_exception+0x168/0x254
>> [    2.264308] softirqs last  enabled at (130070): [<ffff800010080e88>]
>> __do_softirq+0x490/0x56c
>> [    2.272856] softirqs last disabled at (130057): [<ffff800010101e1c>]
>> irq_exit+0x11c/0x148
>> [    2.281057] ---[ end trace 1fae73b5c77d8120 ]---
>> [    2.285792] ------------[ cut here ]------------
> 
> I not met such warning when I test, you enabled lockdep debug?
> 
>>
>> This happens because clk_hw_set_parent does not take the prepare_lock so
>> a lockdep_assert_held fails. In practice it should be mostly harmless because
>> clk operations shouldn't happen while the SOC provider is probing.
>>
>> The issue can be worked around by doing the following instead:
>>
>> +       clk_set_parent(hws[IMX8MQ_CLK_A53_SRC]->clk,
>> hws[IMX8MQ_SYS1_PLL_800M]->clk);
>> +       clk_set_parent(hws[IMX8MQ_CLK_A53_CORE]->clk,
>> hws[IMX8MQ_ARM_PLL_OUT]->clk);
>>
>> This implies reverting commit f95d58981f40 ("clk: imx: Include
>> clk-provider.h instead of clk.h for i.MX8M SoCs clock driver") and
>> somewhat rolls back the consumer/provider split.
>>
>> What would be a clean fix for this? It might make sense to add a new API.
>>
> 
> How about moving this to dts? I'll give a try.

The warning spam still happens in next-20200325.