target/linux/mediatek/patches-5.4/999-2133-pwm-mediatek-add-longer-period-support.patch

From 58d5a373d2d42b5292c1c2242133bcf0b082c6e0 Mon Sep 17 00:00:00 2001
From: Sam Shih <sam.shih@mediatek.com>
Date: Fri, 2 Jun 2023 13:06:07 +0800
Subject: [PATCH] 
 [slow-speed-io][999-2133-pwm-mediatek-add-longer-period-support.patch]

---
 drivers/pwm/pwm-mediatek.c | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/drivers/pwm/pwm-mediatek.c b/drivers/pwm/pwm-mediatek.c
index 9701092e7..79d15a9c0 100644
--- a/drivers/pwm/pwm-mediatek.c
+++ b/drivers/pwm/pwm-mediatek.c
@@ -152,8 +152,11 @@ static int pwm_mediatek_config(struct pwm_chip *chip, struct pwm_device *pwm,
 			       int duty_ns, int period_ns)
 {
 	struct pwm_mediatek_chip *pc = to_pwm_mediatek_chip(chip);
-	u32 clkdiv = 0, cnt_period, cnt_duty, reg_width = PWMDWIDTH,
-	    reg_thres = PWMTHRES;
+	/* The source clock is divided by 2^clkdiv or iff the clksel bit
+	 * is set by (2^clkdiv*1625)
+	 */
+	u32 clkdiv = 0, clksel = 0, cnt_period, cnt_duty,
+	    reg_width = PWMDWIDTH, reg_thres = PWMTHRES;
 	u64 resolution;
 	int ret;
 
@@ -164,12 +167,30 @@ static int pwm_mediatek_config(struct pwm_chip *chip, struct pwm_device *pwm,
 
 	/* Using resolution in picosecond gets accuracy higher */
 	resolution = (u64)NSEC_PER_SEC * 1000;
+	/* Calculate resolution based on current clock frequency */
 	do_div(resolution, clk_get_rate(pc->clk_pwms[pwm->hwpwm]));
-
+	/* Using resolution to calculate cnt_period which represents
+	 * the effective range of the PWM period counter
+	 */
 	cnt_period = DIV_ROUND_CLOSEST_ULL((u64)period_ns * 1000, resolution);
 	while (cnt_period > 8191) {
+		/* Using clkdiv to reduce clock frequency and calculate
+		 * new resolution based on new clock speed
+		 */
 		resolution *= 2;
 		clkdiv++;
+		if (clkdiv > PWM_CLK_DIV_MAX && !clksel) {
+			/* Using clksel to divide the pwm source clock by
+			 * an additional 1625, and recalculate new clkdiv
+			 * and resolution
+			 */
+			clksel = 1;
+			clkdiv = 0;
+			resolution = (u64)NSEC_PER_SEC * 1000 * 1625;
+			do_div(resolution,
+				clk_get_rate(pc->clk_pwms[pwm->hwpwm]));
+		}
+		/* Calculate cnt_period based on resolution */
 		cnt_period = DIV_ROUND_CLOSEST_ULL((u64)period_ns * 1000,
 						   resolution);
 	}
@@ -189,8 +210,13 @@ static int pwm_mediatek_config(struct pwm_chip *chip, struct pwm_device *pwm,
 		reg_thres = PWM45THRES_FIXUP;
 	}
 
+	/* Calculate cnt_duty based on resolution */
 	cnt_duty = DIV_ROUND_CLOSEST_ULL((u64)duty_ns * 1000, resolution);
-	pwm_mediatek_writel(pc, pwm->hwpwm, PWMCON, BIT(15) | clkdiv);
+	if (clksel)
+		pwm_mediatek_writel(pc, pwm->hwpwm, PWMCON, BIT(15) | BIT(3) |
+				    clkdiv);
+	else
+		pwm_mediatek_writel(pc, pwm->hwpwm, PWMCON, BIT(15) | clkdiv);
 	pwm_mediatek_writel(pc, pwm->hwpwm, reg_width, cnt_period);
 	pwm_mediatek_writel(pc, pwm->hwpwm, reg_thres, cnt_duty);
 
-- 
2.34.1