linux-kernel - Re: [PATCH 3/4] ARM: dts: am33xx: Add nodes for eQEP

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Date:   Tue, 23 Jul 2019 09:45:29 -0500
From:   David Lechner <david@...hnology.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     linux-iio@...r.kernel.org, linux-omap@...r.kernel.org,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Benoît Cousson <bcousson@...libre.com>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH 3/4] ARM: dts: am33xx: Add nodes for eQEP

On 7/23/19 3:42 AM, Tony Lindgren wrote:
> * David Lechner <david@...hnology.com> [190722 15:46]:
>> This adds new nodes for the Texas Instruments Enhanced Quadrature
>> Encoder Pulse (eQEP) module in the PWM subsystem on AM33XX.
>>
>> Signed-off-by: David Lechner <david@...hnology.com>
>> ---
>>   arch/arm/boot/dts/am33xx-l4.dtsi | 27 +++++++++++++++++++++++++++
>>   1 file changed, 27 insertions(+)
>>
>> diff --git a/arch/arm/boot/dts/am33xx-l4.dtsi b/arch/arm/boot/dts/am33xx-l4.dtsi
>> index 3b1fb2ba4dff..7fdc2f61c553 100644
>> --- a/arch/arm/boot/dts/am33xx-l4.dtsi
>> +++ b/arch/arm/boot/dts/am33xx-l4.dtsi
>> @@ -1908,6 +1908,15 @@
>>   					status = "disabled";
>>   				};
>>   
>> +				eqep0: eqep@180 {
>> +					compatible = "ti,am3352-eqep";
>> +					reg = <0x180 0x80>;
>> +					clocks = <&l4ls_gclk>;
>> +					clock-names = "fck";
>> +					interrupts = <79>;
>> +					status = "disabled";
>> +				};
>> +
> 
> You probably no longer need to map any clocks here as this> is now a child of the interconnect target module managed
> by ti-sysc driver. I have not checked but probably l4ls_gclk
> is same as clocks = <&l4ls_clkctrl AM3_L4LS_EPWMSS0_CLKCTRL 0>
> already managed by ti-sysc. If so, then just using runtime PM
> calls in any of the child device drivers will keep it enabled.
> 
> If l4ls_gclk is a separate functional clock, then it still
> needs to be managed by the child device driver directly.

The clock is included so that we can get the clock rate for
the timing aspects of the eQEP, not for power management.

I chose to use the "fck" name to be consistent with the
sibling EHRPWM and ECAP nodes that already have the same
bindings for the same clock.