[PATCH 7/9] pwm i.MX: fix clock lookup

On Thu, Sep 06, 2012 at 09:09:42PM +0200, Beno?t Th?baudeau wrote:

On Thursday, September 6, 2012 8:42:56 PM, Sascha Hauer wrote:

quoted

On Thu, Sep 06, 2012 at 08:31:58PM +0200, Beno?t Th?baudeau wrote:

quoted

On Thursday, September 6, 2012 2:48:13 PM, Sascha Hauer wrote:

quoted

+	int ret;
+
+	ret = clk_prepare_enable(imx->clk_ipg);
+	if (ret)
+		return ret;
 
-	return imx->config(chip, pwm, duty_ns, period_ns);
+	ret = imx->config(chip, pwm, duty_ns, period_ns);
+
+	clk_disable_unprepare(imx->clk_ipg);
+
+	return ret;
 }
 
 static int imx_pwm_enable(struct pwm_chip *chip, struct
 pwm_device
 *pwm)

@@ -169,7 +179,7 @@ static int imx_pwm_enable(struct pwm_chip

*chip,
struct pwm_device *pwm)
 	struct imx_chip *imx = to_imx_chip(chip);
 	int ret;
 
-	ret = clk_prepare_enable(imx->clk);
+	ret = clk_prepare_enable(imx->clk_per);
 	if (ret)
 		return ret;

Have you tested that this actually works on i.MX53?

I have tested it successfully on i.MX35 (with a few additions to
platform code).
But i.MX35 has a single bit controlling both PWM IPG and PER clock
gates.

On i.MX53, there are 2 separate control bits for these. So, if ipg
clk is
strictly required to access PWM registers, even if per clk is
enabled, this code
should not work without adding

I tested this on i.MX53, but you're right, this seems to be wrong.
I'll
recheck tomorrow.

I've performed a few more tests with bare register accesses in the bootloader to
see how the PWM IP behaves.

On i.MX25, i.MX35 and i.MX51, read accesses always work, whatever the state of
the IPG and PER clock gates.

On i.MX25 and i.MX51, write accesses always work, whatever the state of the IPG
and PER clock gates.

On i.MX35, write accesses work if and only if the IPG and PER clocks are not
gated off (single control bit for both).

Ok, I tested on i.MX53 and i.MX27.

On i.MX53 the registers are always accessible. I also measured with an
oscilloscope that the ipg/per clock gates en/disable the PWM when it's
configured for the corresponding clock.

On i.MX27 register accesses also work regardless of the clock gates.
Here we have a single clock gate which only gates the ipg clock.

btw the i.MX6 has a single gate per pwm which are described as "PWMx clocks"

So it seems while not 100% correct the current code seems to be safe.

Sascha

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