FAILED: patch "[PATCH] pwm: tiehrpwm: Clear period on disable to allow reconfiguration" failed to apply to 5.15-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x e74b9a7ee50071aad25d3989bf985292f90b0c6e
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107060111-failed-5.15-e74b9a7ee500@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From e74b9a7ee50071aad25d3989bf985292f90b0c6e Mon Sep 17 00:00:00 2001
From: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Date: Tue, 29 Sep 2026 14:08:02 +0200
Subject: [PATCH] pwm: tiehrpwm: Clear period on disable to allow
 reconfiguration
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Both channels share one period register, so ehrpwm_pwm_config() rejects a
period differing from the sibling's period_cycles[]. That value was cleared
only in .free(), not in .disable(), so a stopped channel kept blocking the
sibling from switching to a new frequency. Clear it in .disable() too.

Testcase:

  cd /sys/class/pwm/pwmchip0; echo 0 > export; echo 1 > export
  for p in pwm0 pwm1; do
    echo 1000000 > $p/period; echo 500000 > $p/duty_cycle
    echo 1 > $p/enable; echo 0 > $p/enable; echo 2000000 > $p/period
  done
  echo 1 > pwm0/enable	# before: -EINVAL, after: succeeds

Fixes: 01b2d4536f02 ("pwm: pwm-tiehrpwm: Fix conflicting channel period setting")
Cc: stable@vger.kernel.org
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Link: https://patch.msgid.link/20260929120806.2790355-1-alexander.sverdlin@siemens.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
---
 drivers/pwm/pwm-tiehrpwm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pwm/pwm-tiehrpwm.c b/drivers/pwm/pwm-tiehrpwm.c
index 3a53489f0b982..e3407d0a1f7fe 100644
--- a/drivers/pwm/pwm-tiehrpwm.c
+++ b/drivers/pwm/pwm-tiehrpwm.c
@@ -358,6 +358,9 @@ static void ehrpwm_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
 
 	/* Disable clock on PWM disable */
 	pm_runtime_put_sync(pwmchip_parent(chip));
+
+	/* A disabled channel must not constrain the sibling's period */
+	pc->period_cycles[pwm->hwpwm] = 0;
 }
 
 static void ehrpwm_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
-- 
2.53.0