Messages in this thread | | | Date | Fri, 28 Nov 2014 15:48:00 -0800 | From | Arun Ramamurthy <> | Subject | Re: [PATCH v2 2/4] pwm: kona: Fix incorrect enable after channel polarity change |
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On 14-11-25 10:22 PM, Tim Kryger wrote: > On Tue, Nov 25, 2014 at 11:40 AM, Scott Branden <sbranden@broadcom.com> wrote: >> From: Arun Ramamurthy <arunrama@broadcom.com> >> >> The pwm core code requires a separate call for enabling the channel >> and hence the driver does not need to set pwm_trigger after a >> polarity change > > The framework does restrict when polarity changes can occur but it > isn't clear to me that there is any reason to delay applying the > polarity change. I examined several other drivers such as pwm-atmel-tcb.c, pwm-ep93xx.c, pwm-renesas-tpu.c, pwm-samsung.c in the 3.17 kernel tree and none of them enable the channel after changing polarity. We would be the first driver to do so.
> Keep in mind that polarity matters even when a PWM > is disabled. While disabled, the output should be equivalent to an > enabled configuration with zero duty. Thus for normal polarity the > output is constant low and for inversed polarity the output is > constant high. The driver does set the duty cycle to zero when disabling the pwm channel.However since the frame work prevents polarity change when the pwm is enabled, I don’t see how one could expect the polarity change to be reflected immediately without a separate call to pwm enable.
I believe there is an expectation that the output is > updated to reflect the requested polarity change prior to returning to > the caller.
Once again I disagree with this based on other pwm drivers which only change the polarity and do not enable the channel when their set polarity functions are called.
> >> >> Signed-off-by: Arun Ramamurthy <arunrama@broadcom.com> >> Reviewed-by: Ray Jui <rjui@broadcom.com> >> Signed-off-by: Scott Branden <sbranden@broadcom.com> >> --- >> drivers/pwm/pwm-bcm-kona.c | 5 ----- >> 1 file changed, 5 deletions(-) >> >> diff --git a/drivers/pwm/pwm-bcm-kona.c b/drivers/pwm/pwm-bcm-kona.c >> index 29eef9e..fa0b5bf 100644 >> --- a/drivers/pwm/pwm-bcm-kona.c >> +++ b/drivers/pwm/pwm-bcm-kona.c >> @@ -173,11 +173,6 @@ static int kona_pwmc_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm, >> >> writel(value, kp->base + PWM_CONTROL_OFFSET); >> >> - kona_pwmc_apply_settings(kp, chan); >> - >> - /* Wait for waveform to settle before gating off the clock */ >> - ndelay(400); >> - >> clk_disable_unprepare(kp->clk); >> >> return 0; >> -- >> 2.1.3 >>
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