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

From: Joseph Lo <josephl@nvidia.com>
To: Dmitry Osipenko <digetx@gmail.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>
Subject: Re: [PATCH V5 2/7] clocksource: tegra: add Tegra210 timer support
Date: Sun, 3 Feb 2019 00:07:09 +0800	[thread overview]
Message-ID: <0458731d-e245-8362-2b62-92aa5e1b7fe3@nvidia.com> (raw)
In-Reply-To: <0a5721cc-6cbf-9f1f-6282-36b7175ce9a2@gmail.com>

On 2/2/19 9:38 PM, Dmitry Osipenko wrote:
> 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.
> 

That would be great, thank you.
Joseph