linux-kernel - Re: [PATCH v4 2/4] clocksource/drivers: Add CLINT timer driver

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Message-ID: <107e3ef3-9f61-05d1-7a91-95d0dc7ea7b8@linaro.org>
Date:   Tue, 21 Jul 2020 14:15:56 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Anup Patel <anup@...infault.org>
Cc:     Anup Patel <anup.patel@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Rob Herring <robh+dt@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Damien Le Moal <damien.lemoal@....com>,
        Atish Patra <atish.patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, Emil Renner Berhing <kernel@...il.dk>
Subject: Re: [PATCH v4 2/4] clocksource/drivers: Add CLINT timer driver

On 21/07/2020 13:49, Anup Patel wrote:
> On Tue, Jul 21, 2020 at 4:32 PM Daniel Lezcano
> <daniel.lezcano@...aro.org> wrote:
>>
>> On 17/07/2020 09:50, Anup Patel wrote:
>>> We add a separate CLINT timer driver for Linux RISC-V M-mode (i.e.
>>> RISC-V NoMMU kernel).
>>>
>>> The CLINT MMIO device provides three things:
>>> 1. 64bit free running counter register
>>> 2. 64bit per-CPU time compare registers
>>> 3. 32bit per-CPU inter-processor interrupt registers
>>>
>>> Unlike other timer devices, CLINT provides IPI registers along with
>>> timer registers. To use CLINT IPI registers, the CLINT timer driver
>>> provides IPI related callbacks to arch/riscv.
>>>
>>> Signed-off-by: Anup Patel <anup.patel@....com>
>>> Tested-by: Emil Renner Berhing <kernel@...il.dk>
>>> ---
>>>  drivers/clocksource/Kconfig       |   9 ++
>>>  drivers/clocksource/Makefile      |   1 +
>>>  drivers/clocksource/timer-clint.c | 231 ++++++++++++++++++++++++++++++
>>>  include/linux/cpuhotplug.h        |   1 +
>>>  4 files changed, 242 insertions(+)
>>>  create mode 100644 drivers/clocksource/timer-clint.c
>>>
>>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>>> index 91418381fcd4..e1ce0d510a03 100644
>>> --- a/drivers/clocksource/Kconfig
>>> +++ b/drivers/clocksource/Kconfig
>>> @@ -658,6 +658,15 @@ config RISCV_TIMER
>>>         is accessed via both the SBI and the rdcycle instruction.  This is
>>>         required for all RISC-V systems.
>>>
>>> +config CLINT_TIMER
>>> +     bool "Timer for the RISC-V platform"
>>> +     depends on GENERIC_SCHED_CLOCK && RISCV_M_MODE
>>> +     select TIMER_PROBE
>>> +     select TIMER_OF
>>> +     help
>>> +       This option enables the CLINT timer for RISC-V systems. The CLINT
>>> +       driver is usually used for NoMMU RISC-V systems.
>>
>> V3 has a comment about fixing the Kconfig option.
> 
> I have removed "default y" from the Kconfig option as-per your suggestions.
> 
> I looked at other Timer Kconfig options. Most of them have menuconfig name.
> Also, we can certainly have different timer MMIO timer drivers in future. Do
> you still insist on making this kconfig option totally silent ??

Yes, and there is an effort to change the entries to be silent as much
as possible.

Just add:

	bool "Timer for the RISC-V platform" if COMPILE_TEST

and remove the RISCV_M_MODE dependency.

Or alternatively:

replace the RISCV_M_MODE dependency with COMPILE_TEST

The goal is to be able to compile the driver on different platforms for
compilation test covering.

Then when more mmio drivers will added we will figure out.

>> [ ... ]
>>
>>> +{
>>> +     bool *registered = per_cpu_ptr(&clint_clock_event_registered, cpu);
>>> +     struct clock_event_device *ce = per_cpu_ptr(&clint_clock_event, cpu);
>>> +
>>> +     if (!(*registered)) {
>>> +             ce->cpumask = cpumask_of(cpu);
>>> +             clockevents_config_and_register(ce, clint_timer_freq, 200,
>>> +                                              ULONG_MAX);
>>> +             *registered = true;
>>> +     }
>>
>>
>> I was unsure about the clockevents_config_and_register() multiple calls
>> when doing the comment. It seems like it is fine to call it several
>> times and that is done in several places like riscv or arch_arm_timer.
>>
>> It is probably safe to drop the 'registered' code here, sorry for the
>> confusion.
> 
> Okay, will revert these changes.
> 
>>
>>> +     enable_percpu_irq(clint_timer_irq,
>>> +                       irq_get_trigger_type(clint_timer_irq));
>>> +     return 0;
>>> +}
>>> +
>>
>> [ ... ]
>>
>>
>> --
>> <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
>>
>> Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
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>> <http://www.linaro.org/linaro-blog/> Blog
> 
> Regards,
> Anup
> 


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