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Subject: Re: [PATCH V5 2/7] clocksource: tegra: add Tegra210 timer support
To:     Joseph Lo <josephl@nvidia.com>, Jon Hunter <jonathanh@nvidia.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>
Cc:     linux-tegra@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, Thierry Reding <treding@nvidia.com>
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From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <0a5721cc-6cbf-9f1f-6282-36b7175ce9a2@gmail.com>
Date:   Sat, 2 Feb 2019 16:38:42 +0300
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02.02.2019 2:53, Joseph Lo пишет:
> On 2/2/19 2:08 AM, Dmitry Osipenko wrote:
>> 01.02.2019 18:37, Joseph Lo пишет:
>>> On 2/1/19 11:13 PM, Dmitry Osipenko wrote:
>>>> 01.02.2019 17:13, Joseph Lo пишет:
>>>>> On 2/1/19 9:54 PM, Jon Hunter wrote:
>>>>>>
>>>>>> On 01/02/2019 13:11, Dmitry Osipenko wrote:
>>>>>>> 01.02.2019 16:06, Dmitry Osipenko пишет:
>>>>>>>> 01.02.2019 6:36, Joseph Lo пишет:
>>>>>>>>> Add support for the Tegra210 timer that runs at oscillator clock
>>>>>>>>> (TMR10-TMR13). We need these timers to work as clock event device and to
>>>>>>>>> replace the ARMv8 architected timer due to it can't survive across the
>>>>>>>>> power cycle of the CPU core or CPUPORESET signal. So it can't be a wake-up
>>>>>>>>> source when CPU suspends in power down state.
>>>>>>>>>
>>>>>>>>> Also convert the original driver to use timer-of API.
>>>>>>>>>
>>>>>>>>> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
>>>>>>>>> Cc: Thomas Gleixner <tglx@linutronix.de>
>>>>>>>>> Cc: linux-kernel@vger.kernel.org
>>>>>>>>> Signed-off-by: Joseph Lo <josephl@nvidia.com>
>>>>>>>>> Acked-by: Thierry Reding <treding@nvidia.com>
>>>>>>>>> ---
>>> snip.
>>>>>>>>> +}
>>>>>>>>> +TIMER_OF_DECLARE(tegra210_timer, "nvidia,tegra210-timer", tegra210_timer_init);
>>>>>>>>> +#else /* CONFIG_ARM */
>>>>>>>>> +static int __init tegra20_init_timer(struct device_node *np)
>>>>>>>>> +{
>>>>>>>> What about T132? Isn't it ARM64 which uses tegra20-timer IP? At least T132 DT suggests so and seems this change will break it.
>>>>>>>>
>>>>>>>> [snip]
>>>>>>>>
>>>>>>>
>>>>>>> Ah, noticed the "depends on ARM" in Kconfig.. Seems okay then.
>>>>>>>
>>>>>>
>>>>>>
>>>>>> This is a good point, because even though we had 'depends on ARM', this
>>>>>> still means that the Tegra132 DT is incorrect.
>>>>>>
>>>>>> Joseph, can you take a quick look at Tegra132?
>>>>>
>>>>> Hi Jon and Dmitry,
>>>>>
>>>>> No worry about T132, T132 uses arch timer (v7). The tegra20 timer driver has never been used. We should fix the dtsi file later.
>>>>
>>>> Hi Joseph,
>>>>
>>>> So is T132 HW actually incompatible with the tegra20-timer? If it's compatible, then I think the driver's code should be made more universal to support T132.
>>>>
>>>
>>>  From HW point of view, the TIMER1 ~ TIMER4 is compatible with "nvidia,tegra20-timer". But Tegra132 actually has 10 timers which are exactly the same as Tegra30. So it should backward compatible with "nvidia,tegra30-timer", which is tegra_wdt driver now. And Tegra132 should never use this driver.
>>>
>>> The Tegra timer driver should only be used on Tegra20/30/210, three platforms only. Others use arch timer driver for system timer driver.
>>>
>>> So we don't really need to take care the usage on other Tegra platforms.
>>
>> Doesn't Linux kernel put in use all of available timers? If yes, then we probably would want to expose all available timers. It looks to me that right now tegra20-timer exposes only a single-shared timer to the system [please correct me if I'm wrong]. Wouldn't make sense at least to give a timer per CPU core?
>>
> 
> No, only one timer driver works at a time. ( see /proc/timer_list to check which timer is working.)

Okay, thanks for the clarification.

>> It looks to me that right now tegra20-timer exposes only a single-shared timer to the system [please correct me if I'm wrong]. Wouldn't make sense at least to give a timer per CPU core?
> 
> Yes, it's correct. the timer-tegra20 only provides a single-shared timer. And yes, ,it should provide a timer per CPU core. But that is another task, this patch only introduce the timer support for Tegra210. Others that originally from timer-tegra20 driver still remain the same.

I may take a look at it. Could be better for older Tegra's to use tegra20-timer for the per-CPU timer since TWD timer has some time-jitter due to DVFS.