linux-kernel - Re: [PATCH V3 2/2] timer: imx-tpm: add imx tpm timer support

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Message-ID: <alpine.DEB.2.20.1707041603571.9000@nanos>
Date:   Tue, 4 Jul 2017 16:09:48 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dong Aisheng <aisheng.dong@....com>
cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        daniel.lezcano@...aro.org, shawnguo@...nel.org, ping.bai@....com,
        Anson Huang <anson.huang@....com>, dongas86@...il.com,
        kernel@...gutronix.de, Arnd Bergmann <arnd@...db.de>,
        Anson Huang <Anson.Huang@....com>
Subject: Re: [PATCH V3 2/2] timer: imx-tpm: add imx tpm timer support

On Tue, 4 Jul 2017, Dong Aisheng wrote:

> IMX Timer/PWM Module (TPM) supports both timer and pwm function while
> this patch only adds the timer support. PWM would be added later.
> 
> The TPM counter, compare and capture registers are clocked by an
> asynchronous clock that can remain enabled in low power modes.
> 
> Due to the possible bus fabric contention, the CNT write may
> take a few more cycles and we need add ETIME check in case current
> delta event program gets missed.
> 
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Shawn Guo <shawnguo@...nel.org>
> Cc: Anson Huang <Anson.Huang@....com>
> Cc: Bai Ping <ping.bai@....com>
> Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> 
> ---
> ChangeLog:
> v2->v3:
>  * address all comments from Daniel Lezcano
>  * add more explaination on ETIME check in commit message

Actually the logic wants to be explained in a comment inside the function
as well.

I'm really impressed, that 10 years after we discovered the HPET disaster
(See comment in arch/x86/kernel/hpet.c::hpet_next_event) the same hardware
idiocy comes around again....

Thanks,

	tglx