Messages in this thread | | | From | Olliver Schinagl <> | Subject | Re: [PATCH] pwm: sunxi: wait for the READY bit | Date | Tue, 3 Jan 2017 16:56:16 +0100 |
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Hey Alexandre,
I've sent several patches regarding pwm a while ago, sadly you never responded [0]. So I guess this is a follow up from that?
I couldn't quickly find the resubmitted version however.
Anyway, see below for my comments.
On 03-01-17 15:57, Alexandre Belloni wrote: > 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@free-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; > } > What happens on sun4i here? sun4i does not have the RDY flag, but it does need the PWM_CLK_GATING to be active.
maybe only the readl_poll_timeout() should be guarded by the has_rdy, where you poll the register as you do now, and in the else just have a 'known safe delay' to emulate the has_rdy behavior? I'm guessing a few clock cycles of the PWM block. I don't think the documentation states how long this could/should be.
With my 'wait before disable' patch [1] I run into the same issue, I think. We do not know how long to wait before the hardware is ready.
> + 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, >
[0] https://patchwork.kernel.org/patch/9299635/ [1] https://lkml.org/lkml/2016/9/26/91
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