pwm: imx: Add ipg clock operation

i.MX PWM module's ipg_clk_s is for PWM register access, on most of i.MX
SoCs, this ipg_clk_s is from system ipg clock or perclk which is always
enabled, but on i.MX7D, the ipg_clk_s is from PWM1_CLK_ROOT which is
controlled by CCGR132, that means the CCGR132 MUST be enabled first
before accessing PWM registers on i.MX7D. This patch adds ipg clock
operation to make sure register access successfully on i.MX7D and it
fixes Linux kernel boot up hang during PWM driver probe.

Fixes: 4a23e6e ("ARM: dts: imx7d-sdb: Restore pwm backlight support")
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-imx.c

@@ -87,6 +87,8 @@
 #define MX3_PWMPR_MAX			0xfffe
 
 struct imx_chip {
+	struct clk	*clk_ipg;
+
 	struct clk	*clk_per;
 
 	void __iomem	*mmio_base;
@@ -96,18 +98,48 @@ struct imx_chip {
 
 #define to_imx_chip(chip)	container_of(chip, struct imx_chip, chip)
 
+static int imx_pwm_clk_prepare_enable(struct pwm_chip *chip)
+{
+	struct imx_chip *imx = to_imx_chip(chip);
+	int ret;
+
+	ret = clk_prepare_enable(imx->clk_ipg);
+	if (ret)
+		return ret;
+
+	ret = clk_prepare_enable(imx->clk_per);
+	if (ret) {
+		clk_disable_unprepare(imx->clk_ipg);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void imx_pwm_clk_disable_unprepare(struct pwm_chip *chip)
+{
+	struct imx_chip *imx = to_imx_chip(chip);
+
+	clk_disable_unprepare(imx->clk_per);
+	clk_disable_unprepare(imx->clk_ipg);
+}
+
 static void imx_pwm_get_state(struct pwm_chip *chip,
 		struct pwm_device *pwm, struct pwm_state *state)
 {
 	struct imx_chip *imx = to_imx_chip(chip);
 	u32 period, prescaler, pwm_clk, ret, val;
 	u64 tmp;
 
+	ret = imx_pwm_clk_prepare_enable(chip);
+	if (ret < 0)
+		return;
+
 	val = readl(imx->mmio_base + MX3_PWMCR);
 
 	if (val & MX3_PWMCR_EN) {
 		state->enabled = true;
-		ret = clk_prepare_enable(imx->clk_per);
+		ret = imx_pwm_clk_prepare_enable(chip);
 		if (ret)
 			return;
 	} else {
@@ -143,6 +175,8 @@ static void imx_pwm_get_state(struct pwm_chip *chip,
 	} else {
 		state->duty_cycle = 0;
 	}
+
+	imx_pwm_clk_disable_unprepare(chip);
 }
 
 static int imx_pwm_config_v1(struct pwm_chip *chip,
@@ -180,7 +214,7 @@ static int imx_pwm_enable_v1(struct pwm_chip *chip, struct pwm_device *pwm)
 	u32 val;
 	int ret;
 
-	ret = clk_prepare_enable(imx->clk_per);
+	ret = imx_pwm_clk_prepare_enable(chip);
 	if (ret < 0)
 		return ret;
 
@@ -200,7 +234,7 @@ static void imx_pwm_disable_v1(struct pwm_chip *chip, struct pwm_device *pwm)
 	val &= ~MX1_PWMC_EN;
 	writel(val, imx->mmio_base + MX1_PWMC);
 
-	clk_disable_unprepare(imx->clk_per);
+	imx_pwm_clk_disable_unprepare(chip);
 }
 
 static void imx_pwm_sw_reset(struct pwm_chip *chip)
@@ -286,7 +320,7 @@ static int imx_pwm_apply_v2(struct pwm_chip *chip, struct pwm_device *pwm,
 		if (cstate.enabled) {
 			imx_pwm_wait_fifo_slot(chip, pwm);
 		} else {
-			ret = clk_prepare_enable(imx->clk_per);
+			ret = imx_pwm_clk_prepare_enable(chip);
 			if (ret)
 				return ret;
 
@@ -309,7 +343,7 @@ static int imx_pwm_apply_v2(struct pwm_chip *chip, struct pwm_device *pwm,
 	} else if (cstate.enabled) {
 		writel(0, imx->mmio_base + MX3_PWMCR);
 
-		clk_disable_unprepare(imx->clk_per);
+		imx_pwm_clk_disable_unprepare(chip);
 	}
 
 	return 0;
@@ -367,6 +401,13 @@ static int imx_pwm_probe(struct platform_device *pdev)
 	if (imx == NULL)
 		return -ENOMEM;
 
+	imx->clk_ipg = devm_clk_get(&pdev->dev, "ipg");
+	if (IS_ERR(imx->clk_ipg)) {
+		dev_err(&pdev->dev, "getting ipg clock failed with %ld\n",
+				PTR_ERR(imx->clk_ipg));
+		return PTR_ERR(imx->clk_ipg);
+	}
+
 	imx->clk_per = devm_clk_get(&pdev->dev, "per");
 	if (IS_ERR(imx->clk_per)) {
 		dev_err(&pdev->dev, "getting per clock failed with %ld\n",
@@ -406,6 +447,8 @@ static int imx_pwm_remove(struct platform_device *pdev)
 	if (imx == NULL)
 		return -ENODEV;
 
+	imx_pwm_clk_disable_unprepare(&imx->chip);
+
 	return pwmchip_remove(&imx->chip);
 }