linux-kernel - Re: [PATCH V5 2/7] clocksource: tegra: add Tegra210 timer support

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Date:   Sat, 2 Feb 2019 07:53:46 +0800
From:   Joseph Lo <josephl@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     <linux-tegra@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, Thierry Reding <treding@...dia.com>
Subject: Re: [PATCH V5 2/7] clocksource: tegra: add Tegra210 timer support

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@...aro.org>
>>>>>>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>>>>>>> Cc: linux-kernel@...r.kernel.org
>>>>>>>> Signed-off-by: Joseph Lo <josephl@...dia.com>
>>>>>>>> Acked-by: Thierry Reding <treding@...dia.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.)

 > 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.

Thanks,
Joseph