linux-kernel - Re: [PATCH v2 5/6] clocksource: Add a new timer-ingenic driver

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Message-Id: <1515196105.2058.1@smtp.crapouillou.net>
Date:   Sat, 06 Jan 2018 00:48:25 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     Rob Herring <robh@...nel.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Lee Jones <lee.jones@...aro.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/6] clocksource: Add a new timer-ingenic driver

Hi Rob,

Le sam. 6 janv. 2018 à 0:27, Rob Herring <robh@...nel.org> a écrit :
> On Wed, Jan 3, 2018 at 3:56 PM, Paul Cercueil <paul@...pouillou.net> 
> wrote:
>>  Hi,
>> 
>>  Le mer. 3 janv. 2018 à 22:08, Rob Herring <robh@...nel.org> a 
>> écrit :
>>> 
>>>  On Mon, Jan 01, 2018 at 03:33:43PM +0100, Paul Cercueil wrote:
>>>> 
>>>>   This driver will use the TCU (Timer Counter Unit) present on the 
>>>> Ingenic
>>>>   JZ47xx SoCs to provide the kernel with a clocksource and timers.
>>>> 
>>>>   Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>>>   ---
>>>>    .../devicetree/bindings/timer/ingenic,tcu.txt      |  35 +++
>>> 
>>> 
>>>  Separate patch please.
>> 
>> 
>>  OK.
>> 
>> 
>>>>    drivers/clocksource/Kconfig                        |   8 +
>>>>    drivers/clocksource/Makefile                       |   1 +
>>>>    drivers/clocksource/timer-ingenic.c                | 256
>>>>  +++++++++++++++++++++
>>>>    4 files changed, 300 insertions(+)
>>>>    create mode 100644
>>>>  Documentation/devicetree/bindings/timer/ingenic,tcu.txt
>>>>    create mode 100644 drivers/clocksource/timer-ingenic.c
>>>> 
>>>>    v2: Use SPDX identifier for the license
>>>> 
>>>>   diff --git 
>>>> a/Documentation/devicetree/bindings/timer/ingenic,tcu.txt
>>>>  b/Documentation/devicetree/bindings/timer/ingenic,tcu.txt
>>>>   new file mode 100644
>>>>   index 000000000000..e4944972ea53
>>>>   --- /dev/null
>>>>   +++ b/Documentation/devicetree/bindings/timer/ingenic,tcu.txt
>>>>   @@ -0,0 +1,35 @@
>>>>   +Ingenic JZ47xx SoCs Timer/Counter Unit driver
>>>>   +---------------------------------------------
>>>>   +
>>>>   +Required properties:
>>>>   +
>>>>   +- compatible : should be "ingenic,<socname>-tcu". Valid strings 
>>>> are:
>>>>   +  * ingenic,jz4740-tcu
>>>>   +  * ingenic,jz4770-tcu
>>>>   +  * ingenic,jz4780-tcu
>>>>   +- interrupt-parent : phandle of the TCU interrupt controller.
>>>>   +- interrupts : Specifies the interrupts the controller is 
>>>> connected to.
>>>>   +- clocks : List of phandle & clock specifiers for the TCU 
>>>> clocks.
>>>>   +- clock-names : List of name strings for the TCU clocks.
>>>>   +- ingenic,channels: a list of TCU channels to be used as timers.
>>> 
>>> 
>>>  Why is this needed? This looks like you are trying to assign 
>>> certain
>>>  timers to clocksource and clockevent. A common problem, but one 
>>> that
>>>  should be decided by describing h/w features. There must be some
>>>  property present or missing to make you decide to use a given 
>>> channel or
>>>  not.
>> 
>> 
>>  Well, it's not easy; some TCU channels will be used as PWM, and 
>> there's no
>>  way
>>  to know that when the clocksource driver probes. And which ones are 
>> PWM /
>>  which
>>  ones are not, is board-specific. If you have a better solution 
>> though, I
>>  take it.
> 
> Aren't the PWMs connected to something? Describe those in DT and then
> you can find the free ones.
> 
> Rob

The ingenic PWM driver just creates a PWM chip with 8 channels. Then 
it's up to
the various clients (backlight, rumble...) to request a channel using 
the PWM API,
from their own driver node or pdata. Besides you can also request PWM 
channels
from sysfs... I can't detect all of that...

Paul