linux-kernel - Re: [PATCH v2 02/16] pwm: pxa: update documentation regarding pwm-cells

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Date:   Mon, 22 Jan 2018 10:47:13 +0200
From:   Claudiu Beznea <Claudiu.Beznea@...rochip.com>
To:     Rob Herring <robh@...nel.org>
CC:     <thierry.reding@...il.com>, <mark.rutland@....com>,
        <linux@...linux.org.uk>, <daniel@...que.org>,
        <haojian.zhuang@...il.com>, <robert.jarzmik@...e.fr>,
        <corbet@....net>, <nicolas.ferre@...rochip.com>,
        <alexandre.belloni@...e-electrons.com>,
        <linux-pwm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>,
        <linux-rockchip@...ts.infradead.org>,
        <linux-rpi-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, Mike Dunn <mikedunn@...sguy.com>
Subject: Re: [PATCH v2 02/16] pwm: pxa: update documentation regarding
 pwm-cells



On 20.01.2018 00:30, Rob Herring wrote:
> On Fri, Jan 12, 2018 at 04:22:49PM +0200, Claudiu Beznea wrote:
>> pwm-cells should be at least 2 to provide channel number and period value.
>>
>> Cc: Mike Dunn <mikedunn@...sguy.com>
>> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
>> ---
>>  Documentation/devicetree/bindings/pwm/pxa-pwm.txt | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/pwm/pxa-pwm.txt b/Documentation/devicetree/bindings/pwm/pxa-pwm.txt
>> index 5ae9f1e3c338..a0e20edeeebc 100644
>> --- a/Documentation/devicetree/bindings/pwm/pxa-pwm.txt
>> +++ b/Documentation/devicetree/bindings/pwm/pxa-pwm.txt
>> @@ -10,7 +10,7 @@ Required properties:
>>    Note that one device instance must be created for each PWM that is used, so the
>>    length covers only the register window for one PWM output, not that of the
>>    entire PWM controller.  Currently length is 0x10 for all supported devices.
>> -- #pwm-cells: Should be 1.  This cell is used to specify the period in
>> +- #pwm-cells: Should be 2.  This cell is used to specify the period in
>>    nanoseconds.
> 
> What's the new cell? channel? Does the PXA PWM have more than one 
> channel? If not, then you shouldn't add a cell.
The new cell had to be period, to have a generic OF function in the kernel,
to parse the pwms bindings for all PWMs, something like
pwms=<pwm channel-number pwm-period>. After several discussions on this
series, I found that old DT binaries must be compatible with latest kernel
version and this series doesn't guarantee this. So I will drop this change
in next version.

Thank you,
Claudiu Beznea
> 
> Rob
>