linux-kernel - Re: [PATCH v4 4/8] dt-bindings: Add doc for the Ingenic TCU drivers

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Date:   Thu, 29 Mar 2018 17:59:12 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Rob Herring <robh@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Lee Jones <lee.jones@...aro.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Jonathan Corbet <corbet@....net>,
        Mark Rutland <mark.rutland@....com>,
        James Hogan <jhogan@...nel.org>,
        Maarten ter Huurne <maarten@...ewalker.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux-MIPS <linux-mips@...ux-mips.org>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 4/8] dt-bindings: Add doc for the Ingenic TCU drivers

Hi Rob,

Le mer. 28 mars 2018 à 18:28, Rob Herring <robh@...nel.org> a écrit :
> On Wed, Mar 28, 2018 at 10:33 AM, Paul Cercueil 
> <paul@...pouillou.net> wrote:
>>  Le 2018-03-27 16:46, Rob Herring a écrit :
>>> 
>>>  On Sun, Mar 18, 2018 at 12:28:57AM +0100, Paul Cercueil wrote:
>>>> 
>>>>  Add documentation about how to properly use the Ingenic TCU
>>>>  (Timer/Counter Unit) drivers from devicetree.
>>>> 
>>>>  Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>>>  ---
>>>>   .../bindings/clock/ingenic,tcu-clocks.txt          | 42 
>>>> ++++++++++++++++
>>>>   .../bindings/interrupt-controller/ingenic,tcu.txt  | 39 
>>>> +++++++++++++++
>>>>   .../devicetree/bindings/mfd/ingenic,tcu.txt        | 56
>>>>  ++++++++++++++++++++++
>>>>   .../devicetree/bindings/timer/ingenic,tcu.txt      | 41 
>>>> ++++++++++++++++
>>>>   4 files changed, 178 insertions(+)
>>>>   create mode 100644
>>>>  Documentation/devicetree/bindings/clock/ingenic,tcu-clocks.txt
>>>>   create mode 100644
>>>>  
>>>> Documentation/devicetree/bindings/interrupt-controller/ingenic,tcu.txt
>>>>   create mode 100644 
>>>> Documentation/devicetree/bindings/mfd/ingenic,tcu.txt
>>>>   create mode 100644
>>>>  Documentation/devicetree/bindings/timer/ingenic,tcu.txt
>>>> 
>>>>   v4: New patch in this series. Corresponds to V2 patches 3-4-5 
>>>> with
>>>>   added content.
>>>>  +/ {
>>>>  +       tcu: mfd@...02000 {
>>>>  +               compatible = "ingenic,tcu", "simple-mfd", 
>>>> "syscon";
>>>>  +               reg = <0x10002000 0x1000>;
>>>>  +               #address-cells = <1>;
>>>>  +               #size-cells = <1>;
>>>>  +               ranges = <0x0 0x10002000 0x1000>;
>>>>  +
>>>>  +               tcu_timer: timer@10 {
>>>>  +                       compatible = "ingenic,jz4740-tcu";
>>>>  +                       reg = <0x10 0xff0>;
>>>>  +
>>>>  +                       clocks = <&tcu_clk 0>, <&tcu_clk 1>, 
>>>> <&tcu_clk
>>>>  2>, <&tcu_clk 3>,
>>>>  +                                        <&tcu_clk 4>, <&tcu_clk 
>>>> 5>,
>>>>  <&tcu_clk 6>, <&tcu_clk 7>;
>>>>  +                       clock-names = "timer0", "timer1", 
>>>> "timer2",
>>>>  "timer3",
>>>>  +                                                 "timer4", 
>>>> "timer5",
>>>>  "timer6", "timer7";
>>>>  +
>>>>  +                       interrupt-parent = <&tcu_irq>;
>>>>  +                       interrupts = <0 1 2 3 4 5 6 7>;
>>> 
>>> 
>>>  Thinking about this some more... You simply have 8 timers (and no 
>>> other
>>>  functions?) with some internal clock and irq controls for each 
>>> timer. I
>>>  don't think it really makes sense to create separate clock and irq
>>>  drivers in that case. That would be like creating clock drivers for
>>>  every clock divider in timers, pwms, uarts, etc. Unless the clocks 
>>> get
>>>  exposed to other parts of the system, then there is no point.
>> 
>> 
>>  I have 8 timers with some internal clock and IRQ controls, that can 
>> be used
>>  as PWM.
> 
> Please include how you plan to do the PWM support too. I need a
> complete picture of the h/w, not piecemeal, evolving bindings.

Alright.

>>  But the TCU also controls the IRQ of the OS Timer (which is
>>  separate),
>>  as well as masking of the clocks for the OS timer and the watchdog.
> 
> The OS timer and watchdog are different blocks outside the TCU? This
> doesn't seem to be the case based on the register definitions.

Their register areas are mostly separate, although contiguous. On the 
other
hand, the watchdog and OST can be started/stopped from a bit within a 
TCU
register, so they're probably part of the same h/w block.

>>  I thought having clean drivers for different frameworks working on 
>> the same
>>  regmap was cleaner than having one big-ass driver handling 
>> everything.
> 
> DT is not the only way to instantiate drivers and how one OS splits
> drivers should not define your DT binding. An MFD driver can create
> child devices and a single DT node can be a provider of multiple
> things. It is appropriate for an MFD to have child nodes primarily
> when the sub devices need their own resources defined as properties in
> DT or when the sub device is an IP block reused in multiple devices.
> Just to have a node per driver/provider is not what should drive the
> decision.

The idea is not to have necesarily one node per driver. I just wanted 
to keep
it simple.

Regards,
-Paul