[PATCH 5.18 0301/1095] pwm: lpc18xx: Fix period handling

Greg Kroah-Hartman
2022-08-15T20:56:50Z

From: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

[ Upstream commit 8933d30c5f468d6cc1e4bf9bb535149da35f202e ]

The calculation:

val = (u64)NSEC_PER_SEC * LPC18XX_PWM_TIMER_MAX;
do_div(val, lpc18xx_pwm->clk_rate);
lpc18xx_pwm->max_period_ns = val;

is bogus because with NSEC_PER_SEC = 1000000000,
LPC18XX_PWM_TIMER_MAX = 0xffffffff and clk_rate < NSEC_PER_SEC this
overflows the (on lpc18xx (i.e. ARM32) 32 bit wide) unsigned int
.max_period_ns. This results (dependant of the actual clk rate) in an
arbitrary limitation of the maximal period. E.g. for clkrate =
333333333 (Hz) we get max_period_ns = 9 instead of 12884901897.

So make .max_period_ns an u64 and pass period and duty as u64 to not
discard relevant digits. And also make use of mul_u64_u64_div_u64()
which prevents all overflows assuming clk_rate < NSEC_PER_SEC.

Fixes: 841e6f90bb78 ("pwm: NXP LPC18xx PWM/SCT driver")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/pwm/pwm-lpc18xx-sct.c | 55 +++++++++++++++++++++++++----------
1 file changed, 39 insertions(+), 16 deletions(-)

diff --git a/drivers/pwm/pwm-lpc18xx-sct.c b/drivers/pwm/pwm-lpc18xx-sct.c
index b909096dba2f..43b5509dde51 100644
--- a/drivers/pwm/pwm-lpc18xx-sct.c
+++ b/drivers/pwm/pwm-lpc18xx-sct.c
@@ -98,7 +98,7 @@ struct lpc18xx_pwm_chip {
unsigned long clk_rate;
unsigned int period_ns;
unsigned int min_period_ns;
- unsigned int max_period_ns;
+ u64 max_period_ns;
unsigned int period_event;
unsigned long event_map;
struct mutex res_lock;
@@ -145,40 +145,48 @@ static void lpc18xx_pwm_set_conflict_res(struct lpc18xx_pwm_chip *lpc18xx_pwm,
mutex_unlock(&lpc18xx_pwm->res_lock);
}

-static void lpc18xx_pwm_config_period(struct pwm_chip *chip, int period_ns)
+static void lpc18xx_pwm_config_period(struct pwm_chip *chip, u64 period_ns)
{
struct lpc18xx_pwm_chip *lpc18xx_pwm = to_lpc18xx_pwm_chip(chip);
- u64 val;
+ u32 val;

- val = (u64)period_ns * lpc18xx_pwm->clk_rate;
- do_div(val, NSEC_PER_SEC);
+ /*
+ * With clk_rate < NSEC_PER_SEC this cannot overflow.
+ * With period_ns < max_period_ns this also fits into an u32.
+ * As period_ns >= min_period_ns = DIV_ROUND_UP(NSEC_PER_SEC, lpc18xx_pwm->clk_rate);
+ * we have val >= 1.
+ */
+ val = mul_u64_u64_div_u64(period_ns, lpc18xx_pwm->clk_rate, NSEC_PER_SEC);

lpc18xx_pwm_writel(lpc18xx_pwm,
LPC18XX_PWM_MATCH(lpc18xx_pwm->period_event),
- (u32)val - 1);
+ val - 1);

lpc18xx_pwm_writel(lpc18xx_pwm,
LPC18XX_PWM_MATCHREL(lpc18xx_pwm->period_event),
- (u32)val - 1);
+ val - 1);
}

static void lpc18xx_pwm_config_duty(struct pwm_chip *chip,
- struct pwm_device *pwm, int duty_ns)
+ struct pwm_device *pwm, u64 duty_ns)
{
struct lpc18xx_pwm_chip *lpc18xx_pwm = to_lpc18xx_pwm_chip(chip);
struct lpc18xx_pwm_data *lpc18xx_data = &lpc18xx_pwm->channeldata[pwm->hwpwm];
- u64 val;
+ u32 val;

- val = (u64)duty_ns * lpc18xx_pwm->clk_rate;
- do_div(val, NSEC_PER_SEC);
+ /*
+ * With clk_rate < NSEC_PER_SEC this cannot overflow.
+ * With duty_ns <= period_ns < max_period_ns this also fits into an u32.
+ */
+ val = mul_u64_u64_div_u64(duty_ns, lpc18xx_pwm->clk_rate, NSEC_PER_SEC);

lpc18xx_pwm_writel(lpc18xx_pwm,
LPC18XX_PWM_MATCH(lpc18xx_data->duty_event),
- (u32)val);
+ val);

lpc18xx_pwm_writel(lpc18xx_pwm,
LPC18XX_PWM_MATCHREL(lpc18xx_data->duty_event),
- (u32)val);
+ val);
}

static int lpc18xx_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
@@ -360,12 +368,27 @@ static int lpc18xx_pwm_probe(struct platform_device *pdev)
goto disable_pwmclk;
}

+ /*
+ * If clkrate is too fast, the calculations in .apply() might overflow.
+ */
+ if (lpc18xx_pwm->clk_rate > NSEC_PER_SEC) {
+ ret = dev_err_probe(&pdev->dev, -EINVAL, "pwm clock to fast\n");
+ goto disable_pwmclk;
+ }
+
+ /*
+ * If clkrate is too fast, the calculations in .apply() might overflow.
+ */
+ if (lpc18xx_pwm->clk_rate > NSEC_PER_SEC) {
+ ret = dev_err_probe(&pdev->dev, -EINVAL, "pwm clock to fast\n");
+ goto disable_pwmclk;
+ }
+
mutex_init(&lpc18xx_pwm->res_lock);
mutex_init(&lpc18xx_pwm->period_lock);

- val = (u64)NSEC_PER_SEC * LPC18XX_PWM_TIMER_MAX;
- do_div(val, lpc18xx_pwm->clk_rate);
- lpc18xx_pwm->max_period_ns = val;
+ lpc18xx_pwm->max_period_ns =
+ mul_u64_u64_div_u64(NSEC_PER_SEC, LPC18XX_PWM_TIMER_MAX, lpc18xx_pwm->clk_rate);

lpc18xx_pwm->min_period_ns = DIV_ROUND_UP(NSEC_PER_SEC,
lpc18xx_pwm->clk_rate);
--
2.35.1