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

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Message-ID: <575bfd8e-9246-4acf-ba76-8d5a84689643@ti.com>
Date: Fri, 9 Jan 2026 11:21:46 +0530
From: Gokul Praveen <g-praveen@...com>
To: 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>, Gokul Praveen <g-praveen@...com>
Subject: Re: [PATCH v2] pwm: tiehrpwm: Enable EHRPWM controller before setting
 configuration

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


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