Messages in this thread | | | From | Tim Kryger <> | Date | Thu, 8 Nov 2018 07:32:02 -0800 | Subject | Re: [PATCH 2/2] pwm: bcm-kona: apply pwm settings on enable |
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On Thu, Nov 8, 2018 at 2:59 AM Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote: > > Hello, > > adding Tim Kryger as the initial author of the bcm-kona driver to Cc:. > Maybe he can shed some light to the questions below? > > On Thu, Nov 08, 2018 at 11:47:17AM +0100, Clément Péron wrote: > > On Wed, 7 Nov 2018 at 17:29, Uwe Kleine-König > > <u.kleine-koenig@pengutronix.de> wrote: > > > On Wed, Nov 07, 2018 at 10:36:13AM +0100, Clément Péron wrote: > > > > From: Suji Velupillai <suji.velupillai@broadcom.com> > > > > > > > > When pwm_bl framework calls enable, a call to pwm_is_enabled(pwm) still > > > > return false, this prevents the backlight being turn on at boot time. > > > > > > > > Signed-off-by: Suji Velupillai <suji.velupillai@broadcom.com> > > > > Signed-off-by: Clément Péron <peron.clem@gmail.com> > > > > --- > > > > drivers/pwm/pwm-bcm-kona.c | 16 +++++++++++----- > > > > 1 file changed, 11 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/drivers/pwm/pwm-bcm-kona.c b/drivers/pwm/pwm-bcm-kona.c > > > > index 09a95aeb3a70..d991d53c4b38 100644 > > > > --- a/drivers/pwm/pwm-bcm-kona.c > > > > +++ b/drivers/pwm/pwm-bcm-kona.c > > > > @@ -108,8 +108,8 @@ static void kona_pwmc_apply_settings(struct kona_pwmc *kp, unsigned int chan) > > > > ndelay(400); > > > > } > > > > > > > > -static int kona_pwmc_config(struct pwm_chip *chip, struct pwm_device *pwm, > > > > - int duty_ns, int period_ns) > > > > +static int __pwmc_config(struct pwm_chip *chip, struct pwm_device *pwm, > > > > + int duty_ns, int period_ns, bool pwmc_enabled) > > > > { > > > > struct kona_pwmc *kp = to_kona_pwmc(chip); > > > > u64 val, div, rate; > > > > @@ -155,7 +155,7 @@ static int kona_pwmc_config(struct pwm_chip *chip, struct pwm_device *pwm, > > > > * always calculated above to ensure the new values are > > > > * validated immediately instead of on enable. > > > > */ > > > > - if (pwm_is_enabled(pwm)) { > > > > + if (pwm_is_enabled(pwm) || pwmc_enabled) { > > > > > > Having pwm-API-calls in hw-drivers is ugly. Apart from not giving the > > > intended return code this function should IMHO be reserved to pwm > > > consumers. The underlaying problem is that pwm-bl does: > > > > > > pwm_config(pwm, duty_cycle, period); > > > pwm_enable(pwm); > > > > > > and expects that the duty_cycle and period is used then. Doesn't > > > everything works just fine if the if-block is always executed? > > > > Tested and works fine for me. But I only have a Cygnus proc. > > Maybe there is some issue with Kona as explained by the comment (even > > if I don't understand it well). > > > > * Don't apply settings if disabled. The period and duty cycle are > > * always calculated above to ensure the new values are > > * validated immediately instead of on enable. > > I wouldn't understand that as "If you apply settings on a disabled PWM a > kitten dies". I think it only means: At the current point in time > duty_cycle and period are not important as the hardware is off. So don't > bother to write these values to the hardware. > > @Tim: Do you think (or can test if) there is a problem when doing > > - if (pwm_is_enabled(pwm)) { > + if (1) { > > in kona_pwmc_config? (For sure the comment needs adaption and the if (1) > shouldn't make it into the driver, just used that as shorthand for the > change I want to suggest.) > > But still better than dropping the check is to convert the driver to the > atomic API. With that this problem would simply not occur. > > Best regards > Uwe > > -- > Pengutronix e.K. | Uwe Kleine-König | > Industrial Linux Solutions | http://www.pengutronix.de/ |
There is no per channel disable in the hardware so to simulate a disable, duty is set to zero.
The check is there to prevent new config values from applying until the channel is enabled.
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