[PATCH v2 2/2] pwm: imx: enable clocks during PWM register accesses

[Bastian Krause]

From: Ahmad Fatoum <a.fatoum at pengutronix.de>

This is a port of Linux commit 9f4c8f9607c3147d291b70c13dd01c738ed41faf:

| Author:     Anson Huang <anson.huang at nxp.com>
| AuthorDate: Wed Dec 19 05:24:58 2018 +0000
| Commit:     Thierry Reding <thierry.reding at gmail.com>
| 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 at nxp.com>
|     Signed-off-by: Thierry Reding <thierry.reding at gmail.com>

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.

On top of that, integrate Linux commit
15d4dbd601591858611184f9ddeb5bf21569159c:

| Author:     Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
| AuthorDate: Sun Feb 9 22:31:06 2020 +0100
| Commit:     Thierry Reding <thierry.reding at gmail.com>
| CommitDate: Mon Mar 30 16:55:25 2020 +0200
|
|     pwm: imx27: Fix clock handling in pwm_imx27_apply()
|
|     pwm_imx27_apply() enables the clocks if the previous PWM state was
|     disabled. Given that the clocks are supposed to be left on iff the PWM
|     is running, the decision to disable the clocks at the end of the
|     function must not depend on the previous state.
|
|     Without this fix the enable count of the two affected clocks increases
|     by one whenever ->apply() changes from one disabled state to another.
|
|     Fixes: bd88d319abe9 ("pwm: imx27: Unconditionally write state to hardware")
|     Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
|     Signed-off-by: Thierry Reding <thierry.reding at gmail.com>

In barebox, this means calling imx_pwm_clk_disable_v2() conditionally
iff the PWM is left disabled, otherwise keep the clocks enabled.

Reported-by: Bastian Krause <bst at pengutronix.de>
Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
Reviewed-by: Marco Felsch <m.felsch at pengutronix.de>
Signed-off-by: Bastian Krause <bst at pengutronix.de>
---
Changes since (implicit) v1:
- also port Linux commit 15d4dbd601591858611184f9ddeb5bf21569159c,
  leaving the clocks on iff the PWM is enabled
---
 drivers/pwm/pwm-imx.c | 45 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
index 2dc7e4cfd64..c9db4aef344 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 +162,9 @@ static int imx_pwm_config_v2(struct pwm_chip *chip,
 
 	writel(cr, imx->mmio_base + MX3_PWMCR);
 
+	if (!chip->state.p_enable)
+		imx_pwm_clk_disable_v2(imx);
+
 	return 0;
 }
 
@@ -141,6 +172,11 @@ 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 +186,9 @@ static void imx_pwm_set_enable_v2(struct pwm_chip *chip, bool enable)
 		val &= ~MX3_PWMCR_EN;
 
 	writel(val, imx->mmio_base + MX3_PWMCR);
+
+	if (!enable)
+		imx_pwm_clk_disable_v2(imx);
 }
 
 static int imx_pwm_apply(struct pwm_chip *chip, const struct pwm_state *state)
@@ -215,6 +254,10 @@ 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