From 65c6f742ab14ab1a2679fba72b82dcc0289d96f1 Mon Sep 17 00:00:00 2001 From: Laurentiu Mihalcea Date: Mon, 28 Jul 2025 15:41:44 -0400 Subject: [PATCH] pwm: imx-tpm: Reset counter if CMOD is 0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit As per the i.MX93 TRM, section 67.3.2.1 "MOD register update", the value of the TPM counter does NOT get updated when writing MOD.MOD unless SC.CMOD != 0. Therefore, with the current code, assuming the following sequence: 1) pwm_disable() 2) pwm_apply_might_sleep() /* period is changed here */ 3) pwm_enable() and assuming only one channel is active, if CNT.COUNT is higher than the MOD.MOD value written during the pwm_apply_might_sleep() call then, when re-enabling the PWM during pwm_enable(), the counter will end up resetting after UINT32_MAX - CNT.COUNT + MOD.MOD cycles instead of MOD.MOD cycles as normally expected. Fix this problem by forcing a reset of the TPM counter before MOD.MOD is written. Fixes: 738a1cfec2ed ("pwm: Add i.MX TPM PWM driver support") Cc: stable@vger.kernel.org Signed-off-by: Laurentiu Mihalcea Link: https://lore.kernel.org/r/20250728194144.22884-1-laurentiumihalcea111@gmail.com Signed-off-by: Uwe Kleine-König --- drivers/pwm/pwm-imx-tpm.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/pwm/pwm-imx-tpm.c b/drivers/pwm/pwm-imx-tpm.c index 7ee7b65b9b90c..5b399de16d604 100644 --- a/drivers/pwm/pwm-imx-tpm.c +++ b/drivers/pwm/pwm-imx-tpm.c @@ -204,6 +204,15 @@ static int pwm_imx_tpm_apply_hw(struct pwm_chip *chip, val |= FIELD_PREP(PWM_IMX_TPM_SC_PS, p->prescale); writel(val, tpm->base + PWM_IMX_TPM_SC); + /* + * if the counter is disabled (CMOD == 0), programming the new + * period length (MOD) will not reset the counter (CNT). If + * CNT.COUNT happens to be bigger than the new MOD value then + * the counter will end up being reset way too late. Therefore, + * manually reset it to 0. + */ + if (!cmod) + writel(0x0, tpm->base + PWM_IMX_TPM_CNT); /* * set period count: * if the PWM is disabled (CMOD[1:0] = 2b00), then MOD register -- 2.47.2