[PATCH v3 3/3] leds: rgb: leds-qcom-lpg: Fix calculation of best period Hi-Res PWMs

Abel Vesa
2025-03-03T11:53:15Z

When determining the actual best period by looping through all
possible PWM configs, the resolution currently used is based on
bit shift value which is off-by-one above the possible maximum
PWM value allowed.

So subtract one from the resolution before determining the best
period so that the maximum duty cycle requested by the PWM user
won't result in a value above the maximum allowed.

Cc: stable@vger.kernel.org # 6.4
Fixes: b00d2ed37617 ("leds: rgb: leds-qcom-lpg: Add support for high resolution PWM")
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
---
drivers/leds/rgb/leds-qcom-lpg.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
index 0b6310184988c299d82ee7181982c03d306407a4..4f2a178e3d265a2cc88e651d3e2ca6ae3dfac2e2 100644
--- a/drivers/leds/rgb/leds-qcom-lpg.c
+++ b/drivers/leds/rgb/leds-qcom-lpg.c
@@ -462,7 +462,7 @@ static int lpg_calc_freq(struct lpg_channel *chan, uint64_t period)
max_res = LPG_RESOLUTION_9BIT;
}

- min_period = div64_u64((u64)NSEC_PER_SEC * (1 << pwm_resolution_arr[0]),
+ min_period = div64_u64((u64)NSEC_PER_SEC * ((1 << pwm_resolution_arr[0]) - 1),
clk_rate_arr[clk_len - 1]);
if (period <= min_period)
return -EINVAL;
@@ -483,7 +483,7 @@ static int lpg_calc_freq(struct lpg_channel *chan, uint64_t period)
*/

for (i = 0; i < pwm_resolution_count; i++) {
- resolution = 1 << pwm_resolution_arr[i];
+ resolution = (1 << pwm_resolution_arr[i]) - 1;
for (clk_sel = 1; clk_sel < clk_len; clk_sel++) {
u64 numerator = period * clk_rate_arr[clk_sel];

@@ -1292,7 +1292,7 @@ static int lpg_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
if (ret)
return ret;

- state->period = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC * (1 << resolution) *
+ state->period = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC * ((1 << resolution) - 1) *
pre_div * (1 << m), refclk);
state->duty_cycle = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC * pwm_value * pre_div * (1 << m), refclk);
} else {

--
2.34.1