linux-kernel - Re: [PATCH 1/7] add binding for stm32 multifunctions timer driver

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Message-ID: <CA+M3ks6rnago88JC0C5Uj6JpGZGuwyoOj-W8+r7Oj4s8_GuXyA@mail.gmail.com>
Date:   Wed, 23 Nov 2016 18:02:01 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...aro.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     robh+dt@...nel.org, Mark Rutland <mark.rutland@....com>,
        alexandre.torgue@...com, devicetree@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-pwm@...r.kernel.org, jic23@...nel.org, knaack.h@....de,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Fabrice Gasnier <fabrice.gasnier@...com>,
        Gerald Baeza <gerald.baeza@...com>,
        Arnaud Pouliquen <arnaud.pouliquen@...com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
        Benjamin Gaignard <benjamin.gaignard@...com>
Subject: Re: [PATCH 1/7] add binding for stm32 multifunctions timer driver

2016-11-23 10:21 GMT+01:00 Lee Jones <lee.jones@...aro.org>:
> On Wed, 23 Nov 2016, Benjamin Gaignard wrote:
>
>> 2016-11-22 17:52 GMT+01:00 Lee Jones <lee.jones@...aro.org>:
>> > On Tue, 22 Nov 2016, Benjamin Gaignard wrote:
>> >
>> >> Add bindings information for stm32 timer MFD
>> >>
>> >> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...com>
>> >> ---
>> >>  .../devicetree/bindings/mfd/stm32-timer.txt        | 53 ++++++++++++++++++++++
>> >>  1 file changed, 53 insertions(+)
>> >>  create mode 100644 Documentation/devicetree/bindings/mfd/stm32-timer.txt
>> >>
>> >> diff --git a/Documentation/devicetree/bindings/mfd/stm32-timer.txt b/Documentation/devicetree/bindings/mfd/stm32-timer.txt
>> >> new file mode 100644
>> >> index 0000000..3cefce1
>> >> --- /dev/null
>> >> +++ b/Documentation/devicetree/bindings/mfd/stm32-timer.txt
>> >> @@ -0,0 +1,53 @@
>> >> +STM32 multifunctions timer driver
>> >
>> > "STM32 Multi-Function Timer/PWM device bindings"
>> >
>> > Doesn't this shared device have a better name?
>>
>> In SoC documentation those hardware blocks are named "advanced-control
>> timers", "general purpose timers" or "basic timers"
>> "stm32-timer" name is already used for clock source driver, that why I
>> have prefix it with mfd
>
> MFD is a Linuxisum and has no place in hardware description.
>
> Please used one of the names you mentioned above.

I will go for "st,stm32-advanced-timer"

>
> Hopefully the one that best fits.
>
>> >> +stm32 timer MFD allow to handle at the same time pwm and IIO timer devices
>> >
>> > No need for this sentence.
>> >
>> OK
>>
>> >> +Required parameters:
>> >> +- compatible: must be one of the follow value:
>> >> +     "st,stm32-mfd-timer1"
>> >> +     "st,stm32-mfd-timer2"
>> >> +     "st,stm32-mfd-timer3"
>> >> +     "st,stm32-mfd-timer4"
>> >> +     "st,stm32-mfd-timer5"
>> >> +     "st,stm32-mfd-timer6"
>> >> +     "st,stm32-mfd-timer7"
>> >> +     "st,stm32-mfd-timer8"
>> >> +     "st,stm32-mfd-timer9"
>> >> +     "st,stm32-mfd-timer10"
>> >> +     "st,stm32-mfd-timer11"
>> >> +     "st,stm32-mfd-timer12"
>> >> +     "st,stm32-mfd-timer13"
>> >> +     "st,stm32-mfd-timer14"
>> >
>> > We don't normally number devices.
>> >
>> > What's stopping you from simply doing:
>> >
>> >         pwm1: pwm1@...10000 {
>> >                 compatible = "st,stm32-pwm";
>> >         };
>> >         pwm2: pwm1@...20000 {
>> >                 compatible = "st,stm32-pwm";
>> >         };
>> >         pwm3: pwm1@...30000 {
>> >                 compatible = "st,stm32-pwm";
>> >         };
>> >
>>
>> Because each instance of the hardware is slightly different: number of
>> pwm channels, triggers capabilities, etc ..
>> so I need to distinguish them.
>> Since it look to be a problem I will follow your suggestion and add a
>> property this driver to be able to identify each instance.
>> Do you think that "id" parameter (integer for 1 to 14) is acceptable ?
>
> Unfortunately not. IDs aren't allowed in DT.
>
> What about "pwm-chans" and "trigger"?
>
> pwm-chans              : Number of available channels available

For pwm I need those 4 properties:
st,pwm-number: the number of PWM devices
st,complementary: if exist have complementary ouput
st,32bit-counter: if exist have 32 bits counter
st,breakinput-polarity: if set enable break input feature.

Is it acceptable from pwm maintainer point of view ?

> trigger                : Boolean value specifying whether a timer is present

Following our discussion on IRC I will try to code for your proposal:

advanced-timer@...10000 {
        compatible = "st,stm32-advanced-timer";
        reg = <0x40010000 0x400>;
        clocks = <&rcc 0 160>;
        clock-names = "clk_int";

        pwm@0 {
                compatible = "st,stm32-pwm";
                st,pwm-number= <4>;
                st,complementary;
                st,breakinput;
        };

        timer@0 {
                reg = <1>;
                compatible = "st,stm32-iio-timer";
                interrupts = <27>;
                triggers = <5 2 3 4>;
        };
};

triggers parameter will be used to know which trigger are valid for
the IIO device

[snip]