pwm: imx27: Ensure clocks being on iff the PWM is on

Up to now the .probe() function didn't enable clocks and relied on the
core to call the .get_state() callback to have the clock running. The
latter enabled the needed clocks and kept them running if the PWM wass
enabled.

This only works correctly if the .get_state() callback is called exactly
once and this single call happens before unused clocks are disabled by
the clk core.

The former wasn't true for a short period while commit 01ccf903
("pwm: Let pwm_get_state() return the last implemented state") applied
and not reverted yet and might become wrong in the future.

The latter isn't true any more since commit cfc4c189 ("pwm: Read
initial hardware state at request time") which results in a running PWM
being stopped at boot time if for example the consumer lives in a kernel
module that is only loaded after the clk core disabled unused clocks.

So ensure .probe() is left with the clocks on if the PWM is running and
.get_state() disables everything it enabled.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-imx27.c

@@ -171,8 +171,7 @@ static void pwm_imx27_get_state(struct pwm_chip *chip,
 	tmp = NSEC_PER_SEC * (u64)(val);
 	state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, pwm_clk);
 
-	if (!state->enabled)
-		pwm_imx27_clk_disable_unprepare(imx);
+	pwm_imx27_clk_disable_unprepare(imx);
 }
 
 static void pwm_imx27_sw_reset(struct pwm_chip *chip)
@@ -307,6 +306,8 @@ MODULE_DEVICE_TABLE(of, pwm_imx27_dt_ids);
 static int pwm_imx27_probe(struct platform_device *pdev)
 {
 	struct pwm_imx27_chip *imx;
+	int ret;
+	u32 pwmcr;
 
 	imx = devm_kzalloc(&pdev->dev, sizeof(*imx), GFP_KERNEL);
 	if (imx == NULL)
@@ -349,6 +350,15 @@ static int pwm_imx27_probe(struct platform_device *pdev)
 	if (IS_ERR(imx->mmio_base))
 		return PTR_ERR(imx->mmio_base);
 
+	ret = pwm_imx27_clk_prepare_enable(imx);
+	if (ret)
+		return ret;
+
+	/* keep clks on if pwm is running */
+	pwmcr = readl(imx->mmio_base + MX3_PWMCR);
+	if (!(pwmcr & MX3_PWMCR_EN))
+		pwm_imx27_clk_disable_unprepare(imx);
+
 	return pwmchip_add(&imx->chip);
 }