linux-kernel - [PATCH v2] leds: qcom-lpg: Fix PWM period limits

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Date:   Mon, 15 May 2023 09:26:04 -0700
From:   Bjorn Andersson <quic_bjorande@...cinc.com>
To:     Pavel Machek <pavel@....cz>, Lee Jones <lee@...nel.org>,
        "Anjelique Melendez" <quic_amelende@...cinc.com>
CC:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, <linux-leds@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        Caleb Connolly <caleb.connolly@...aro.org>,
        Steev Klimaszewski <steev@...i.org>
Subject: [PATCH v2] leds: qcom-lpg: Fix PWM period limits

The introduction of high resolution PWM support changed the order of the
operations in the calculation of min and max period. The result in both
divisions is in most cases a truncation to 0, which limits the period to
the range of [0, 0].

Both numerators (and denominators) are within 64 bits, so the whole
expression can be put directly into the div64_u64, instead of doing it
partially.

Fixes: b00d2ed37617 ("leds: rgb: leds-qcom-lpg: Add support for high resolution PWM")
Reviewed-by: Caleb Connolly <caleb.connolly@...aro.org>
Tested-by: Steev Klimaszewski <steev@...i.org>
Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>
---

Changes since v1:
- Reworded first sentence to express that it's the order and not the
  previously non-existent parenthesis that changed...
- Picked up review tags.

 drivers/leds/rgb/leds-qcom-lpg.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
index c9cea797a697..7287fadc00df 100644
--- a/drivers/leds/rgb/leds-qcom-lpg.c
+++ b/drivers/leds/rgb/leds-qcom-lpg.c
@@ -312,14 +312,14 @@ static int lpg_calc_freq(struct lpg_channel *chan, uint64_t period)
 		max_res = LPG_RESOLUTION_9BIT;
 	}
 
-	min_period = (u64)NSEC_PER_SEC *
-			div64_u64((1 << pwm_resolution_arr[0]), clk_rate_arr[clk_len - 1]);
+	min_period = div64_u64((u64)NSEC_PER_SEC * (1 << pwm_resolution_arr[0]),
+			       clk_rate_arr[clk_len - 1]);
 	if (period <= min_period)
 		return -EINVAL;
 
 	/* Limit period to largest possible value, to avoid overflows */
-	max_period = (u64)NSEC_PER_SEC * max_res * LPG_MAX_PREDIV *
-			div64_u64((1 << LPG_MAX_M), 1024);
+	max_period = div64_u64((u64)NSEC_PER_SEC * max_res * LPG_MAX_PREDIV * (1 << LPG_MAX_M),
+			       1024);
 	if (period > max_period)
 		period = max_period;
 
-- 
2.25.1