linux-kernel - Re: [PATCH v7 05/24] clocksource: Add a new timer-ingenic driver

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Message-ID: <e5104bd9-1564-266d-4f27-affa8a9e825d@linaro.org>
Date:   Mon, 24 Sep 2018 07:58:42 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Mathieu Malaterre <malat@...ian.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>, linux-doc@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        linux-watchdog@...r.kernel.org, od@...c.me,
        linux-mips@...ux-mips.org, Paul Burton <paul.burton@...s.com>,
        Mark Rutland <mark.rutland@....com>, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Ralf Baechle <ralf@...ux-mips.org>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-pwm@...r.kernel.org
Subject: Re: [PATCH v7 05/24] clocksource: Add a new timer-ingenic driver

On 24/09/2018 07:49, Paul Cercueil wrote:
> 
> Le 24 sept. 2018 07:35, Daniel Lezcano <daniel.lezcano@...aro.org> a
> écrit :
>> 
>> On 24/09/2018 07:24, Paul Cercueil wrote:
>>> Hi Daniel,
>>> 
>>> Le 24 sept. 2018 05:12, Daniel Lezcano
>>> <daniel.lezcano@...aro.org> a écrit :
>>>> 
>>>> On 21/08/2018 19:16, Paul Cercueil wrote:
>>>>> This driver handles the TCU (Timer Counter Unit) present on
>>>>> the Ingenic JZ47xx SoCs, and provides the kernel with a
>>>>> system timer, and optionally with a clocksource and a
>>>>> sched_clock.
>>>>> 
>>>>> It also provides clocks and interrupt handling to client
>>>>> drivers.
>>>> 
>>>> Can you provide a much more complete description of the timer
>>>> in order to make my life easier for the review of this patch?
>>> 
>>> See patch [03/24], it adds a doc file that describes the
>>> hardware.
>> 
>> Thanks, I went through but it is incomplete to understand what the
>> timer do. I will reverse-engineer the code but it would help if you
>> can give the gross approach. Why multiple channels ? mutexes and
>> completion ?
> 
> Much of the complexity is because of the multi-purpose nature of the
> TCU channels. Each one can be used as timer/clocksource, or PWM.
> 
> The driver starts by using channels 0 and 1 as system timer and
> clocksource, respectively, the other ones being unused for now. Then,
> *if* the PWM driver requests one of the channels in use by the
> timer/clocksource driver, say channel 0, the timer/clocksource driver
> will dynamically reassign the system timer to a free channel, from
> channel 0 to e.g. channel 2. Only in that case the completion/mutex
> are actually used.

Why do you need to do this? Can't be the channels dedicated and reserved
for clocksource and clockevent?


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