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

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Date:   Mon, 24 Sep 2018 09:14:26 +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,
        linux-watchdog@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        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 08:53, Paul Cercueil wrote:
> 
> Le 24 sept. 2018 07:58, Daniel Lezcano <daniel.lezcano@...aro.org> a écrit :
>>
>> 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? 
> 
> That's what I had in place (ingenic,timer-channel and ingenic,clocksource-channel DT properties), but Rob didn't want any linux-specific properties in the devicetree binding :(

Isn't possible to specify the channel to use in the DT? like renesas16 ?

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