[PATCH master 2/2] pwm: imx: enable clocks during PWM register accesses

[Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>]

This is a port of Linux commit 9f4c8f9607c3147d291b70c13dd01c738ed41faf:

| Author:     Anson Huang <anson.huang@xxxxxxx>
| AuthorDate: Wed Dec 19 05:24:58 2018 +0000
| Commit:     Thierry Reding <thierry.reding@xxxxxxxxx>
| CommitDate: Mon Dec 24 12:06:56 2018 +0100
|
|     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: 4a23e6ee9f69 ("ARM: dts: imx7d-sdb: Restore pwm backlight support")
|     Signed-off-by: Anson Huang <Anson.Huang@xxxxxxx>
|     Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxx>

Unlike the Linux version, we make clk_ipg optional to reduce changes for
older SoCs.

This fixes system hang during PWM access on i.MX8M and presumably i.MX7.

Reported-by: Bastian Krause <bst@xxxxxxxxxxxxxx>
Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
---
 drivers/pwm/pwm-imx.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
index 2dc7e4cfd64d..486ca962f96d 100644
--- a/drivers/pwm/pwm-imx.c
+++ b/drivers/pwm/pwm-imx.c
@@ -36,7 +36,7 @@
 #define MX3_PWMCR_EN              (1 << 0)
 
 struct imx_chip {
-	struct clk	*clk_per;
+	struct clk	*clk_per, *clk_ipg;
 
 	void __iomem	*mmio_base;
 
@@ -93,14 +93,42 @@ static void imx_pwm_set_enable_v1(struct pwm_chip *chip, bool enable)
 	writel(val, imx->mmio_base + MX1_PWMC);
 }
 
+static int imx_pwm_clk_enable_v2(struct imx_chip *imx)
+{
+	int ret;
+
+	ret = clk_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_v2(struct imx_chip *imx)
+{
+	clk_disable_unprepare(imx->clk_per);
+	clk_disable_unprepare(imx->clk_ipg);
+}
+
 static int imx_pwm_config_v2(struct pwm_chip *chip,
 		int duty_ns, int period_ns)
 {
 	struct imx_chip *imx = to_imx_chip(chip);
 	unsigned long long c;
 	unsigned long period_cycles, duty_cycles, prescale;
+	int ret;
 	u32 cr;
 
+	ret = imx_pwm_clk_enable_v2(imx);
+	if (ret)
+		return ret;
+
 	c = clk_get_rate(imx->clk_per);
 	c = c * period_ns;
 	do_div(c, 1000000000);
@@ -134,6 +162,8 @@ static int imx_pwm_config_v2(struct pwm_chip *chip,
 
 	writel(cr, imx->mmio_base + MX3_PWMCR);
 
+	imx_pwm_clk_disable_v2(imx);
+
 	return 0;
 }
 
@@ -141,6 +171,11 @@ static void imx_pwm_set_enable_v2(struct pwm_chip *chip, bool enable)
 {
 	struct imx_chip *imx = to_imx_chip(chip);
 	u32 val;
+	int ret;
+
+	ret = imx_pwm_clk_enable_v2(imx);
+	if (WARN_ON(ret))
+		return;
 
 	val = readl(imx->mmio_base + MX3_PWMCR);
 
@@ -150,6 +185,8 @@ static void imx_pwm_set_enable_v2(struct pwm_chip *chip, bool enable)
 		val &= ~MX3_PWMCR_EN;
 
 	writel(val, imx->mmio_base + MX3_PWMCR);
+
+	imx_pwm_clk_disable_v2(imx);
 }
 
 static int imx_pwm_apply(struct pwm_chip *chip, const struct pwm_state *state)
@@ -215,6 +252,10 @@ static int imx_pwm_probe(struct device *dev)
 
 	imx = xzalloc(sizeof(*imx));
 
+	imx->clk_ipg = clk_get_optional(dev, "ipg");
+	if (IS_ERR(imx->clk_ipg))
+		return PTR_ERR(imx->clk_ipg);
+
 	imx->clk_per = clk_get(dev, "per");
 	if (IS_ERR(imx->clk_per))
 		return PTR_ERR(imx->clk_per);
-- 
2.39.2