From dc9e08fdbcc3eb08a1d2b868b535081c44425e27 Mon Sep 17 00:00:00 2001 From: Ronaldo Nunez Date: Fri, 22 May 2026 16:13:48 -0300 Subject: [PATCH] pwm: imx27: Fix variable truncation in .apply() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Fix a variable truncation when calculating period in microseconds as part of the solution for the ERR051198 in .apply() callback. Example scenario: - Period of 3us (PWMPR = 196 and prescaler = 1) - Expected value in tmp: 198000000000 (NSEC_PER_SEC * (196 + 2) * 1) - Actual value is 431504384 (truncation to u32) Signed-off-by: Ronaldo Nunez Reviewed-by: Frank Li Link: https://patch.msgid.link/20260522191348.6227-1-rnunez@baylibre.com Fixes: a25351e4c774 ("pwm: imx27: Workaround of the pwm output bug when decrease the duty cycle") Signed-off-by: Uwe Kleine-König --- drivers/pwm/pwm-imx27.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c index 3d34cdc4a3a5..c8b801fcb525 100644 --- a/drivers/pwm/pwm-imx27.c +++ b/drivers/pwm/pwm-imx27.c @@ -200,7 +200,7 @@ static void pwm_imx27_wait_fifo_slot(struct pwm_chip *chip, static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm, const struct pwm_state *state) { - unsigned long period_cycles, duty_cycles, prescale, period_us, tmp; + unsigned long period_cycles, duty_cycles, prescale, period_us; struct pwm_imx27_chip *imx = to_pwm_imx27_chip(chip); unsigned long long c; unsigned long long clkrate; @@ -208,6 +208,7 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm, int val; int ret; u32 cr; + u64 tmp; clkrate = clk_get_rate(imx->clks[PWM_IMX27_PER].clk); c = clkrate * state->period; @@ -249,6 +250,11 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm, val = readl(imx->mmio_base + MX3_PWMPR); val = val >= MX3_PWMPR_MAX ? MX3_PWMPR_MAX : val; cr = readl(imx->mmio_base + MX3_PWMCR); + + /* + * tmp stores period in nanoseconds. Result fits in u64 since + * val <= 0xfffe and prescaler in [1, 0x1000]. + */ tmp = NSEC_PER_SEC * (u64)(val + 2) * MX3_PWMCR_PRESCALER_GET(cr); tmp = DIV_ROUND_UP_ULL(tmp, clkrate); period_us = DIV_ROUND_UP_ULL(tmp, 1000);