pwm: imx27: Fix variable truncation in .apply()

[ Upstream commit dc9e08f ]

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 <rnunez@baylibre.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260522191348.6227-1-rnunez@baylibre.com
Fixes: a25351e ("pwm: imx27: Workaround of the pwm output bug when decrease the duty cycle")
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Ronaldo Nunez

drivers/pwm/pwm-imx27.c

@@ -200,14 +200,15 @@ 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;
 	unsigned long flags;
 	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);