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

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Message-ID: <3527b094-5b39-473a-afc1-cfca7baeb3d1@ti.com>
Date: Thu, 15 Jan 2026 11:44:47 +0530
From: Gokul Praveen <g-praveen@...com>
To: "Kumar, Udit" <u-kumar1@...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>, Gokul Praveen <g-praveen@...com>
Subject: Re: [PATCH v2] pwm: tiehrpwm: Enable EHRPWM controller before setting
 configuration

Hi Udit,

On 15/01/26 10:50, Kumar, Udit wrote:
> 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 .
> 
> 
> 

Can you change the last command to the following. Ideally , it should be 
a different duty cycle set to enter into the driver code.

 >> /sys/class/pwm/pwmchip0/pwm0# echo 6000000 > duty_cycle

Best Regards
Gokul Praveen
>>
>>
>> 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
>>
>>
>>