linux-kernel - Re: [PATCH v2] pwm: tiehrpwm: Enable EHRPWM controller before setting configuration

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Message-ID: <85d941a6-9c57-45f3-ab6a-33ca91cf05a5@ti.com>
Date: Thu, 15 Jan 2026 10:50:06 +0530
From: "Kumar, Udit" <u-kumar1@...com>
To: Gokul Praveen <g-praveen@...com>, Uwe Kleine-König
	<ukleinek@...nel.org>
CC: "Rafael V. Volkmer" <rafael.v.volkmer@...il.com>, <j-keerthy@...com>,
	<linux-kernel@...r.kernel.org>, <linux-pwm@...r.kernel.org>,
	<n-francis@...com>, <u-kumar1@...com>
Subject: Re: [PATCH v2] pwm: tiehrpwm: Enable EHRPWM controller before setting
 configuration

Hello Gokul,

On 1/9/2026 11:21 AM, Gokul Praveen wrote:
> Hi Uwe,
>
>
> On 08/01/26 23:40, Uwe Kleine-König wrote:
>> Hello Gokul,
>>
>> On Thu, Jan 08, 2026 at 12:10:35PM +0530, Gokul Praveen wrote:
>>> On 08/01/26 01:17, Rafael V. Volkmer wrote:
>>>> Thanks for CC'ing me on this thread.
>>>>
>>>> On 07/01/26 15:21, Uwe Kleine-König wrote:
>>>>> adding Rafael to Cc: who sent a patch series for this driver that I
>>>>> didn't come around to review yet. Given that neither he nor me 
>>>>> noticed
>>>>> the problem addressed in this patch I wonder if it applies to all
>>>>> hardware variants.
>>>>>
>>>>
>>>> I also didn't observe the issue described here in my testing: duty 
>>>> cycle and
>>>> period changes always appeared to take effect as expected.
>>>>
>>>> My tests were done on an AM623 EVM.
>>>>
>>>> One possible explanation is that my test flow mostly exercised 
>>>> configuration
>>>> while the PWM was already enabled/active, which could mask the 
>>>> effect of a
>>>> put_sync/reset happening after configuration.
>>>>
>>>
>>> Yes, this is the reason why the configuration was taking effect for 
>>> you ,
>>> Rafael, as the PWM was already enabled when setting the 
>>> configuration hence
>>> masking the effect of a put_sync/reset happening after configuration.
>>
>> Can you provide a list of commands that show the failure? That would
>> result in less guessing for me. My plan is to reproduce the failure
>> tomorrow to better understand it on my boneblack.
>>
>> Best regards
>> Uwe
>
> Sure Uwe. These are the commands I have tried for PWM signal generation:
>
> cd /sys/class/pwm/pwmchip0
> /sys/class/pwm/pwmchip0# echo 0 > export
> /sys/class/pwm/pwmchip0# cd pwm0/
> /sys/class/pwm/pwmchip0/pwm0# echo 10000000 > period
> /sys/class/pwm/pwmchip0/pwm0# echo 3000000 > duty_cycle
> /sys/class/pwm/pwmchip0/pwm0# echo "normal" > polarity
> /sys/class/pwm/pwmchip0/pwm0# echo 1 > enable
>
> Once these commands were executed, I measured the PWM signal using 
> logic analyzer and the duty cycle was 100% even though we had set 30% 
> duty cycle through the sysfs nodes.
>
> However, with the below command sequence, the duty cycle was getting 
> set properly
>
> cd /sys/class/pwm/pwmchip0
> /sys/class/pwm/pwmchip0# echo 0 > export
> /sys/class/pwm/pwmchip0# cd pwm0/
> /sys/class/pwm/pwmchip0/pwm0# echo 10000000 > period
> /sys/class/pwm/pwmchip0/pwm0# echo 3000000 > duty_cycle
> /sys/class/pwm/pwmchip0/pwm0# echo "normal" > polarity
> /sys/class/pwm/pwmchip0/pwm0# echo 1 > enable
> /sys/class/pwm/pwmchip0/pwm0# echo 3000000 > duty_cycle


I don't think , this last call of setting duty_cycle , even will land in 
driver code .



>
>
> PWM is working only if we re-update the duty cycle after enabling the 
> module.
>
> If we do not re-update the duty cycle after enabling the module then 
> PWM signal line is being high(100 % duty) always.
>
> Test Environment: TI J784S4 EVM board.
>
> Best Regards
> Gokul Praveen
>
>
>