linux-kernel - [PATCH v2 1/2] leds: rgb: leds-qcom-lpg: Fix pwm resolution max for Hi-Res PWMs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250226-leds-qcom-lpg-fix-max-pwm-on-hi-res-v2-1-7af5ef5d220b@linaro.org>
Date: Wed, 26 Feb 2025 15:58:54 +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 1/2] leds: rgb: leds-qcom-lpg: Fix pwm resolution max
 for Hi-Res PWMs

Ideally, the requested duty cycle should never translate to a PWM
value higher than the selected resolution (PWM size), but currently the
best matched period is never reported back to the PWM consumer, so the
consumer will still be using the requested period which is higher than
the best matched one. This will result in PWM consumer requesting
duty cycle values higher than the allowed PWM value.

Currently, the consumer driver known to fail this way is the PWM backlight
(pwm_bl) and should be reworked in such a way that the best matched period
is used instead.

As for the current implementation of the duty cycle calculation, it is
capping the max value, fix that by using the resolution to figure out the
maximum allowed PWM value.

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 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
index f3c9ef2bfa572f9ee86c8b8aa37deb8231965490..146cd9b447787bf170310321e939022dfb176e9f 100644
--- a/drivers/leds/rgb/leds-qcom-lpg.c
+++ b/drivers/leds/rgb/leds-qcom-lpg.c
@@ -529,7 +529,7 @@ static void lpg_calc_duty(struct lpg_channel *chan, uint64_t duty)
 	unsigned int clk_rate;

 	if (chan->subtype == LPG_SUBTYPE_HI_RES_PWM) {
-		max = LPG_RESOLUTION_15BIT - 1;
+		max = BIT(lpg_pwm_resolution_hi_res[chan->pwm_resolution_sel]) - 1;
 		clk_rate = lpg_clk_rates_hi_res[chan->clk_sel];
 	} else {
 		max = LPG_RESOLUTION_9BIT - 1;

-- 
2.34.1