[PATCH 5.4 062/102] pwm: sun4i: Fix incorrect calculation of duty_cycle/period

Greg Kroah-Hartman
2020-01-24T09:40:14Z

From: Ondrej Jirman <megous@megous.com>

[ Upstream commit 50cc7e3e4f26e3bf5ed74a8d061195c4d2161b8b ]

Since 5.4-rc1, pwm_apply_state calls ->get_state after ->apply
if available, and this revealed an issue with integer precision
when calculating duty_cycle and period for the currently set
state in ->get_state callback.

This issue manifested in broken backlight on several Allwinner
based devices.

Previously this worked, because ->apply updated the passed state
directly.

Fixes: deb9c462f4e53 ("pwm: sun4i: Don't update the state for the caller of pwm_apply_state")
Signed-off-by: Ondrej Jirman <megous@megous.com>
Acked-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-sun4i.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
index 6f5840a1a82dc..05273725a9fff 100644
--- a/drivers/pwm/pwm-sun4i.c
+++ b/drivers/pwm/pwm-sun4i.c
@@ -137,10 +137,10 @@ static void sun4i_pwm_get_state(struct pwm_chip *chip,

val = sun4i_pwm_readl(sun4i_pwm, PWM_CH_PRD(pwm->hwpwm));

- tmp = prescaler * NSEC_PER_SEC * PWM_REG_DTY(val);
+ tmp = (u64)prescaler * NSEC_PER_SEC * PWM_REG_DTY(val);
state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, clk_rate);

- tmp = prescaler * NSEC_PER_SEC * PWM_REG_PRD(val);
+ tmp = (u64)prescaler * NSEC_PER_SEC * PWM_REG_PRD(val);
state->period = DIV_ROUND_CLOSEST_ULL(tmp, clk_rate);
}

--
2.20.1