linux-kernel - Re: [PATCH v2 01/16] drivers: pwm: core: use a single of xlate function

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Date:   Tue, 16 Jan 2018 10:24:59 +0200
From:   Claudiu Beznea <Claudiu.Beznea@...rochip.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Brian Norris <briannorris@...omium.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Jonathan Corbet <corbet@....net>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        <linux-pwm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>,
        <linux-rockchip@...ts.infradead.org>,
        <linux-rpi-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        Mike Dunn <mikedunn@...sguy.com>,
        Alexander Shiyan <shc_work@...l.ru>
Subject: Re: [PATCH v2 01/16] drivers: pwm: core: use a single of xlate
 function



On 15.01.2018 22:27, Andy Shevchenko wrote:
> On Mon, Jan 15, 2018 at 10:41 AM, Claudiu Beznea
> <Claudiu.Beznea@...rochip.com> wrote:
> 
>> For this driver, the PWM bindings were changed (I did a grep by "google,cros-ec-pwm"
>> and located only:
>> arch/arm64/boot/dts/rockchip/rk3399-gru-kevin.dts
>> arch/arm64/boot/dts/rockchip/rk3399-gru.dtsi
>> files) and changed the bindings in this series, as follows, patch 7 from this series:
>> diff --git a/arch/arm64/boot/dts/rockchip/rk3399-gru-kevin.dts b/arch/arm64/boot/dts/rockchip/rk3399-gru-kevin.dts
>> index 0384e3121f18..0c790ec387eb 100644
>> --- a/arch/arm64/boot/dts/rockchip/rk3399-gru-kevin.dts
>> +++ b/arch/arm64/boot/dts/rockchip/rk3399-gru-kevin.dts
>> @@ -77,7 +77,7 @@
>>
>>         backlight: backlight {
>>                 compatible = "pwm-backlight";
>> -               pwms = <&cros_ec_pwm 1>;
>> +               pwms = <&cros_ec_pwm 1 65535>;
> 
> This shows an breakage for user.
As long as pwm-cells=2 the OF hooks will read PWM channel and PWM period
(e.g. in this case, PWM channel=1, PWM period=65532)
I don't see a breakage here. Please explain me further.

The old PWM device tree sources or
> binaries should work independently on what changes you did to kernel.
Please explain me further. From this I understand, as a general rule,
that the device tree binaries from, e.g. 3 years ago, should be
compatible with, e.g. the current version of kernel?

Thanks,
Claudiu
>