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

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Message-ID: <xkhyvqemt7ox6s3kcwjx2qktwlrvdo2dbn2azlk6tdimjvclky@g3btsovrn5am>
Date: Mon, 19 Jan 2026 22:33:25 +0100
From: Uwe Kleine-König <ukleinek@...nel.org>
To: "Kumar, Udit" <u-kumar1@...com>
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
Subject: Re: [PATCH v2] pwm: tiehrpwm: Enable EHRPWM controller before
 setting configuration

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));
+
 	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

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