linux-kernel - [PATCH v2 2/2] leds: rgb: leds-qcom-lpg: Fix calculation of best period Hi-Res PWMs

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Message-Id: <20250226-leds-qcom-lpg-fix-max-pwm-on-hi-res-v2-2-7af5ef5d220b@linaro.org>
Date: Wed, 26 Feb 2025 15:58:55 +0200
From: Abel Vesa <abel.vesa@...aro.org>
To: Lee Jones <lee@...nel.org>, Pavel Machek <pavel@...nel.org>, 
 Anjelique Melendez <quic_amelende@...cinc.com>
Cc: Kamal Wadhwa <quic_kamalw@...cinc.com>, 
 Jishnu Prakash <jishnu.prakash@....qualcomm.com>, 
 Bjorn Andersson <andersson@...nel.org>, 
 Konrad Dybcio <konradybcio@...nel.org>, Johan Hovold <johan@...nel.org>, 
 Sebastian Reichel <sre@...nel.org>, Pavel Machek <pavel@....cz>, 
 linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Abel Vesa <abel.vesa@...aro.org>, stable@...r.kernel.org
Subject: [PATCH v2 2/2] leds: rgb: leds-qcom-lpg: Fix calculation of best
 period Hi-Res PWMs

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@...r.kernel.org    # 6.4
Fixes: b00d2ed37617 ("leds: rgb: leds-qcom-lpg: Add support for high resolution PWM")
Signed-off-by: Abel Vesa <abel.vesa@...aro.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 146cd9b447787bf170310321e939022dfb176e9f..5d8e27e2e7ae71c19637b90cc15eb363c53317d9 100644
--- a/drivers/leds/rgb/leds-qcom-lpg.c
+++ b/drivers/leds/rgb/leds-qcom-lpg.c
@@ -461,7 +461,7 @@ 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;
@@ -482,7 +482,7 @@ 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];
 
@@ -1291,7 +1291,7 @@ 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