linux-kernel - Re: [PATCH] clocksource: Add driver for the Ingenic JZ47xx OST

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Date:   Thu, 07 Nov 2019 20:57:58 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, od@...c.me,
        linux-kernel@...r.kernel.org,
        Maarten ter Huurne <maarten@...ewalker.org>,
        Mathieu Malaterre <malat@...ian.org>,
        Artur Rojek <contact@...ur-rojek.eu>
Subject: Re: [PATCH] clocksource: Add driver for the Ingenic JZ47xx OST



Le jeu., nov. 7, 2019 at 20:39, Daniel Lezcano 
<daniel.lezcano@...aro.org> a écrit :
> On 07/11/2019 16:56, Paul Cercueil wrote:
>>  Hi Daniel,
>> 
>>  On 2019-08-16 16:54, Daniel Lezcano wrote:
>>>  On 09/08/2019 14:38, Paul Cercueil wrote:
>>>>  From: Maarten ter Huurne <maarten@...ewalker.org>
>>>> 
>>>>  OST is the OS Timer, a 64-bit timer/counter with buffered reading.
>>>> 
>>>>  SoCs before the JZ4770 had (if any) a 32-bit OST; the JZ4770 and
>>>>  JZ4780 have a 64-bit OST.
>>>> 
>>>>  This driver will register both a clocksource and a sched_clock to 
>>>> the
>>>>  system.
>>>> 
>>>>  Signed-off-by: Maarten ter Huurne <maarten@...ewalker.org>
>>>>  Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>>>  Tested-by: Mathieu Malaterre <malat@...ian.org>
>>>>  Tested-by: Artur Rojek <contact@...ur-rojek.eu>
>>>>  ---
>>>> 
>>> 
>>>  [ ... ]
>>> 
>>>>  +    err = clocksource_register_hz(cs, rate);
>>>>  +    if (err) {
>>>>  +        dev_err(dev, "clocksource registration failed: %d\n", 
>>>> err);
>>>>  +        clk_disable_unprepare(ost->clk);
>>>>  +        return err;
>>>>  +    }
>>>>  +
>>>>  +    /* Cannot register a sched_clock with interrupts on */
>>> 
>>>  Aren't they already disabled?
>> 
>>  Sorry for the late reply.
>> 
>>  No, they are not already disabled; this is what I get if I comment 
>> out
>>  the local_irq_save()/local_irq_restore():
>> 
>>  [    0.361014] clocksource: ingenic-ost: mask: 0xffffffff 
>> max_cycles:
>>  0xffffffff, max_idle_ns: 159271703898 ns
>>  [    0.361515] clocksource: Switched to clocksource ingenic-ost
>>  [    0.361686] ------------[ cut here ]------------
>>  [    0.361893] WARNING: CPU: 0 PID: 1 at 
>> kernel/time/sched_clock.c:179
>>  sched_clock_register+0x7c/0x2e4
>>  [    0.362174] CPU: 0 PID: 1 Comm: swapper Not tainted 5.4.0-rc5+ 
>> #461
>>  [    0.362330] Stack : 80744558 80069b44 80770000 00000000 00000000
>>  00dfd7a7 806e6db4 8106bb74
>>  [    0.362619]         806f0000 81067ca4 806f31c7 80769478 00000020
>>  10000400 8106bb20 00dfd7a7
>>  [    0.362906]         00000000 00000000 80780000 00000000 00000007
>>  00000001 00000049 3563722d
>>  [    0.363191]         8106ba61 00000000 ffffffff 00000010 806f0000
>>  00000000 00000000 806f0000
>>  [    0.363477]         00000020 00000000 80714534 80770000 00000002
>>  80319154 00000000 80770000
>>  [    0.363762]         ...
>>  [    0.363906] Call Trace:
>>  [    0.364087] [<8001af14>] show_stack+0x40/0x128
>>  [    0.364289] [<8002fd88>] __warn+0xb8/0xe0
>>  [    0.364478] [<8002fe14>] warn_slowpath_fmt+0x64/0xc0
>>  [    0.364678] [<8072b1c8>] sched_clock_register+0x7c/0x2e4
>>  [    0.364895] [<8073c874>] ingenic_ost_probe+0x224/0x248
>>  [    0.365090] [<803d5394>] platform_drv_probe+0x40/0x94
>>  [    0.365526] [<803d362c>] really_probe+0x104/0x374
>>  [    0.365743] [<803d3ff0>] device_driver_attach+0x78/0x80
>>  [    0.365938] [<803d4070>] __driver_attach+0x78/0x118
>>  [    0.366129] [<803d1700>] bus_for_each_dev+0x7c/0xc8
>>  [    0.366318] [<803d226c>] bus_add_driver+0x1bc/0x204
>>  [    0.366513] [<803d4878>] driver_register+0x84/0x14c
>>  [    0.366717] [<8073a144>] __platform_driver_probe+0x98/0x140
>>  [    0.366931] [<80724e38>] do_one_initcall+0x84/0x1b4
>>  [    0.367126] [<807250cc>] kernel_init_freeable+0x164/0x240
>>  [    0.367318] [<805df75c>] kernel_init+0x10/0xf8
>>  [    0.367510] [<8001542c>] ret_from_kernel_thread+0x14/0x1c
>>  [    0.367722] ---[ end trace 7fedf00408fa3bed ]---
>>  [    0.367985] sched_clock: 32 bits at 12MHz, resolution 83ns, wraps
>>  every 178956970966ns
>> 
>>  At kernel/time/sched_clock.c:179 there is:
>>  WARN_ON(!irqs_disabled());
> 
> That is strange, no drivers is doing that and no warning is appearing.
> 
> Isn't missing a local_irq_disable in the code path in the stack above?

I think it comes to the fact that the other drivers are probed much 
earlier in the boot process, while this one is probed as a regular 
platform device driver.

> 
>>>>  +    local_irq_save(flags);
>>>>  +    if (soc_info->is64bit)
>>>>  +        sched_clock_register(ingenic_ost_read_cntl, 32, rate);
>>>>  +    else
>>>>  +        sched_clock_register(ingenic_ost_read_cnth, 32, rate);
>>>>  +    local_irq_restore(flags);
>>>>  +
>>>>  +    return 0;
>>>>  +}
>>>>  +
> 
> 
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