linux-kernel - [PATCH] pwm: sunxi: wait for the READY bit

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Message-Id: <20170103145732.2108-1-alexandre.belloni@free-electrons.com>
Date:   Tue,  3 Jan 2017 15:57:32 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>, linux-pwm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Olliver Schinagl <oliver@...inagl.nl>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Subject: [PATCH] pwm: sunxi: wait for the READY bit

Most of the call sites in the kernel are not really prepared to handle
-EBUSY when calling pwm_config(). This means that they will either fail
silently or fail without letting the user retry at a later time.

This can be seen for example when using pwm-backlight (the most common use
case for this driver). It will first call pwm_config() with a 0 duty cycle
and disable the pwm. Then it will call pwm_config() that fails because the
pwm had no chance to update its period internally and
pwm_enable() ending up with a duty cycle of 0.

Instead, actually wait for the RDY bit to go low before continuing.

Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
---
 drivers/pwm/pwm-sun4i.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
index b0803f6c64d9..be489388e006 100644
--- a/drivers/pwm/pwm-sun4i.c
+++ b/drivers/pwm/pwm-sun4i.c
@@ -10,6 +10,7 @@
 #include <linux/clk.h>
 #include <linux/err.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
@@ -103,7 +104,7 @@ static int sun4i_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	u32 prd, dty, val, clk_gate;
 	u64 clk_rate, div = 0;
 	unsigned int prescaler = 0;
-	int err;
+	int err = 0;
 
 	clk_rate = clk_get_rate(sun4i_pwm->clk);
 
@@ -154,18 +155,22 @@ static int sun4i_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	spin_lock(&sun4i_pwm->ctrl_lock);
 	val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
 
-	if (sun4i_pwm->data->has_rdy && (val & PWM_RDY(pwm->hwpwm))) {
-		spin_unlock(&sun4i_pwm->ctrl_lock);
-		clk_disable_unprepare(sun4i_pwm->clk);
-		return -EBUSY;
-	}
-
 	clk_gate = val & BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
-	if (clk_gate) {
-		val &= ~BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
+
+	if (sun4i_pwm->data->has_rdy && (val & PWM_RDY(pwm->hwpwm))) {
+		val |= BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
 		sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
+
+		err = readl_poll_timeout(sun4i_pwm->base + PWM_CTRL_REG, val,
+					 !(val & PWM_RDY(pwm->hwpwm)), 400,
+					 500000);
+		if (err)
+			goto finish;
 	}
 
+	val &= ~BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
+	sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
+
 	val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
 	val &= ~BIT_CH(PWM_PRESCAL_MASK, pwm->hwpwm);
 	val |= BIT_CH(prescaler, pwm->hwpwm);
@@ -174,6 +179,7 @@ static int sun4i_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	val = (dty & PWM_DTY_MASK) | PWM_PRD(prd);
 	sun4i_pwm_writel(sun4i_pwm, val, PWM_CH_PRD(pwm->hwpwm));
 
+finish:
 	if (clk_gate) {
 		val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
 		val |= clk_gate;
@@ -183,7 +189,7 @@ static int sun4i_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	spin_unlock(&sun4i_pwm->ctrl_lock);
 	clk_disable_unprepare(sun4i_pwm->clk);
 
-	return 0;
+	return err;
 }
 
 static int sun4i_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
-- 
2.11.0