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

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Message-ID: <80a2c59a-fe7a-4244-a374-bfc70dc46978@ti.com>
Date: Tue, 20 Jan 2026 10:10:02 +0530
From: "Kumar, Udit" <u-kumar1@...com>
To: Uwe Kleine-König <ukleinek@...nel.org>
CC: Gokul Praveen <g-praveen@...com>, "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

Hi Uwe,

On 1/20/2026 3:03 AM, Uwe Kleine-König wrote:
> On Mon, Jan 19, 2026 at 08:30:08PM +0530, Kumar, Udit wrote:
>> Hi Uwe/Gokul,
>>
>> On 1/12/2026 12:52 PM, Uwe Kleine-König wrote:
>>> Hello Gokul,
>>>
>>> On Mon, Jan 12, 2026 at 11:21:50AM +0530, Gokul Praveen wrote:
>>>> On 10/01/26 04:23, Uwe Kleine-König wrote:
>>>>> As I cannot reproduce the issue, can you please check if adding
>>>>>
>>>>> 	pm_runtime_get_sync(pwmchip_parent(chip));
>>>>>
>>>>> to the probe function makes the problem disappear? Also please boot with
>>>>>
>>>>> 	trace_event=pwm
>>>>>
>>>>> on the command line and provide the content of
>>>>> /sys/kernel/debug/tracing/trace after reproducing the problem.
>>>> sure Uwe, I will try this from my side.
>>>>
>>>> In the meantime, will you able to test the same on TI J784S4 EVM as the
>>>> issue was reproduced on this board.
>>> I don't have such hardware, sorry. The boards with TI SoC on my desk are
>>> only a Beaglebone Black and a BeaglePlay. (And I didn't setup the
>>> BeaglePlay yet, it was already quite a hassle to make the boneblack work
>>> with a recent kernel. In the end it looks trivial, but
>>> https://salsa.debian.org/kernel-team/linux/-/merge_requests/1777 plus
>>> unreliable netbooting in the bootloader took me several hours to sort
>>> out.)
>> I am able to see this issue on J7200 hardware ,
>>
>> LTM, it may work on certain devices, depending upon how LPSC (Local power
>> state controller) and PSC (power state controller))
>>
>> are managed.
>>
>> In original code , while putting sync at
>>
>> https://elixir.bootlin.com/linux/v6.18.6/source/drivers/pwm/pwm-tiehrpwm.c#L293
>>
>>
>> will leads to calling genpd driver [0], which may put PWM IP in powered down
>> state, leading to loosing contents.
>>
>> So, we need retain pm count (genpd on in fact) between config and enable
>> call.
>>
>> Therefore this patch LGTM
> I doesn't look good to me, it's way to complicated. Unless I still
> misunderstand something, I think
>
> diff --git a/drivers/pwm/pwm-tiehrpwm.c b/drivers/pwm/pwm-tiehrpwm.c
> index 7a86cb090f76..4942689105f3 100644
> --- a/drivers/pwm/pwm-tiehrpwm.c
> +++ b/drivers/pwm/pwm-tiehrpwm.c
> @@ -378,6 +378,8 @@ static int ehrpwm_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>   	int err;
>   	bool enabled = pwm->state.enabled;
>   
> +	guard(pm_runtime_active)(pwmchip_parent(chip));
> +


Fair point,  only need i see to keep in hardware active state after 
dropping count at

https://elixir.bootlin.com/linux/v6.18.6/source/drivers/pwm/pwm-tiehrpwm.c#L293 


Above changes will achieve same as well.


>   	if (state->polarity != pwm->state.polarity) {
>   		if (enabled) {
>   			ehrpwm_pwm_disable(chip, pwm);
>
> is enough to fix the issue. (We need something like
> https://lore.kernel.org/linux-pwm/20251123233349.2122-1-rafael.v.volkmer@gmail.com/
> to make this really robust.)
>
> Best regards
> Uwe