[PATCH AUTOSEL 5.4 053/205] pwm: sun4i: Fix incorrect calculation of duty_cycle/period

From: Ondrej Jirman <redacted>

[ 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 <redacted>
Acked-by: Uwe Kleine-König <redacted>
Signed-off-by: Thierry Reding <redacted>
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 6f5840a1a82d..05273725a9ff 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


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On Thu, Jan 16, 2020 at 11:40:28AM -0500, Sasha Levin wrote:

From: Ondrej Jirman <redacted>

[ 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 <redacted>
Acked-by: Uwe Kleine-König <redacted>
Signed-off-by: Thierry Reding <redacted>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Note that while the patch is still correct, the problem isn't that bad
any more since commit 01ccf903edd65f6421612321648fa5a7f4b7cb10 was
reverted.

So .get_state is only called once during boot where the breakage doesn't
hurt that much.

I let you decide if you still want to apply this patch.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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