[PATCH 6.0 0778/1073] pwm: tegra: Improve required rate calculation

Greg Kroah-Hartman
2022-12-28T16:26:51Z

From: Jon Hunter <jonathanh@nvidia.com>

[ Upstream commit f271946117dde2ca8741b8138b347b2d68e6ad56 ]

For the case where dev_pm_opp_set_rate() is called to set the PWM clock
rate, the requested rate is calculated as ...

required_clk_rate = (NSEC_PER_SEC / period_ns) << PWM_DUTY_WIDTH;

The above calculation may lead to rounding errors because the
NSEC_PER_SEC is divided by 'period_ns' before applying the
PWM_DUTY_WIDTH multiplication factor. For example, if the period is
45334ns, the above calculation yields a rate of 5646848Hz instead of
5646976Hz. Fix this by applying the multiplication factor before
dividing and using the DIV_ROUND_UP macro which yields the expected
result of 5646976Hz.

Fixes: 1d7796bdb63a ("pwm: tegra: Support dynamic clock frequency configuration")
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-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-tegra.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pwm/pwm-tegra.c b/drivers/pwm/pwm-tegra.c
index dad9978c9186..b05ea2e8accc 100644
--- a/drivers/pwm/pwm-tegra.c
+++ b/drivers/pwm/pwm-tegra.c
@@ -145,8 +145,8 @@ static int tegra_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
* source clock rate as required_clk_rate, PWM controller will
* be able to configure the requested period.
*/
- required_clk_rate =
- (NSEC_PER_SEC / period_ns) << PWM_DUTY_WIDTH;
+ required_clk_rate = DIV_ROUND_UP_ULL(NSEC_PER_SEC << PWM_DUTY_WIDTH,
+ period_ns);

err = dev_pm_opp_set_rate(pc->dev, required_clk_rate);
if (err < 0)
--
2.35.1