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Subject: Re: [PATCH v3 0/6] clocksource: rework Atmel TCB timer driver
To:     Alexander Dahl <ada@thorsis.com>,
        linux-arm-kernel@lists.infradead.org
Cc:     Alexandre Belloni <alexandre.belloni@bootlin.com>,
        linux-kernel@vger.kernel.org,
        Boris Brezillon <boris.brezillon@bootlin.com>,
        Thomas Gleixner <tglx@linutronix.de>
References: <20180223171558.7037-1-alexandre.belloni@bootlin.com>
 <9761072.pX2B0LJlSJ@ada>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
Message-ID: <989df8a3-462a-c645-87f1-9f956e1b22c9@linaro.org>
Date:   Tue, 27 Mar 2018 13:30:22 +0200
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On 27/03/2018 12:41, Alexander Dahl wrote:
> Hello Alexandre,
> 
> Am Freitag, 23. Februar 2018, 18:15:52 CEST schrieb Alexandre Belloni:
>>  - using the PIT doesn't work well with preempt-rt because its interrupt is
>>    shared (in particular with the UART and their interrupt flags are
>>    incompatible)
> 
> This is actually quite annoying when using the UART as a serial console, 
> producing garbage when you type too fast. That's why I tested this patch 
> series (on top of v4.16-rc7). Target is a at91sam9g20 based board, quite close 
> to, but not actually an at91sam9g20-ek.
> 
> First test was with the previous kernel config updated by oldconfig, so 
> basically still using the PIT:
> 
>   +CONFIG_ATMEL_CLOCKSOURCE_PIT=y
> 
> On the serial console with v4.16 and the patch set without switching to the 
> new options, I see this on boot (no surprise, this is what it also prints with 
> v4.9):
> 
>   clocksource: pit: mask: 0xfffffff max_cycles: 0xfffffff, max_idle_ns: 
> 14468723050 ns
>   …
>   clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 
> 19112604462750000 ns
>   …
>   clocksource: tcb_clksrc: mask: 0xffffffff max_cycles: 0xffffffff, 
> max_idle_ns: 115749784805 ns
>   …
>   clocksource: Switched to clocksource tcb_clksrc
> 
> Interrupts here:
> 
>   $ cat /proc/interrupts 
>              CPU0       
>    16:       4802  atmel-aic   1 Level     at91_tick, rtc0, ttyS0
>    19:      24041  atmel-aic  19 Level     tc_clkevt
>    26:        124  atmel-aic  21 Level     eth0
>    28:          1      GPIO  11 Edge      reset
>   Err:          0
> 
> Second test with tcb block added to dts like in 
> 32ce250b0af3b6971fc746445fce87861a9f5628 and with changed kernel config 
> according to defconfig changes in patch 5 and 6:
> 
>   +# CONFIG_ATMEL_CLOCKSOURCE_PIT is not set
>   +CONFIG_ATMEL_CLOCKSOURCE_TCB=y
>   -CONFIG_ATMEL_TCLIB=y
>   -CONFIG_ATMEL_TCB_CLKSRC=y
>   -CONFIG_ATMEL_TCB_CLKSRC_BLOCK=0
>   +# CONFIG_ATMEL_TCLIB is not set
>   -CONFIG_ATMEL_PIT=y
>   +CONFIG_ATMEL_ARM_TCB_CLKSRC=y
>   -CONFIG_PWM_ATMEL_TCB=m
> 
> The output on the serial console contains this:
> 
>   clocksource: timer@fffa0000:0,1: mask: 0xffffffff max_cycles: 0xffffffff, 
> max_idle_ns: 115749784805 ns
>   …
>   clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 
> 19112604462750000 ns
>   …
>   clocksource: Switched to clocksource timer@fffa0000:0,1
> 
> Interrupts here:
> 
>   $ cat /proc/interrupts 
>              CPU0       
>    17:    5727291  atmel-aic  19 Level     timer@fffa0000:2
>    18:       5523  atmel-aic   1 Level     rtc0, ttyS0
>    26:       5031  atmel-aic  21 Level     eth0
>    28:          1      GPIO  11 Edge      reset
>   Err:          0
> 
> So, the board boots and runs like usual. I don't know if that qualifies for a 
> Tested-by? Hope that helps.

Can you can give a rough amount for the irq rate on the timer ?


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