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Date: Wed, 6 May 2015 21:26:00 -0700
From: Tim Kryger <tim.kryger@...il.com>
To: Jonathan Richardson <jonathar@...adcom.com>
Cc: Dmitry Torokhov <dtor@...gle.com>,
Anatol Pomazau <anatol@...gle.com>,
Arun Ramamurthy <arun.ramamurthy@...adcom.com>,
Thierry Reding <thierry.reding@...il.com>,
Scott Branden <sbranden@...adcom.com>,
bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux PWM <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v6 3/4] pwm: kona: Fix incorrect config, disable, and
polarity procedures
On Fri, Apr 10, 2015 at 11:58 AM, Jonathan Richardson
<jonathar@...adcom.com> wrote:
> The polarity procedure no longer applies the settings to change the
> output signal because it can't be called when the pwm is enabled anyway.
> The polarity is only updated in the control register. The correct
> polarity will be applied on enable. The old method of applying changes
> would result in no signal when the polarity was changed. The new
> apply_settings function would fix this problem but it isn't required
> anyway.
Why does this bug fix need to alter when polarity changes take effect?
That is an an unrelated change and I don't really agree with it.
> /* If duty_ns or period_ns are not achievable then return */
> - if (pc < PERIOD_COUNT_MIN || dc < DUTY_CYCLE_HIGH_MIN)
> + if (pc < PERIOD_COUNT_MIN) {
> + dev_warn(chip->dev,
> + "%s: pwm[%d]: period=%d is not achievable, pc=%lu, prescale=%lu\n",
> + __func__, chan, period_ns, pc, prescale);
> + return -EINVAL;
> + }
> +
> + /* If duty_ns is not achievable then return */
> + if (dc < DUTY_CYCLE_HIGH_MIN) {
> + if (0 != duty_ns) {
> + dev_warn(chip->dev,
> + "%s: pwm[%d]: duty cycle=%d is not achievable, dc=%lu, prescale=%lu\n",
> + __func__, chan, duty_ns, dc, prescale);
> + }
> return -EINVAL;
> + }
>
> /* If pc and dc are in bounds, the calculation is done */
> if (pc <= PERIOD_COUNT_MAX && dc <= DUTY_CYCLE_HIGH_MAX)
> break;
>
> /* Otherwise, increase prescale and recalculate pc and dc */
> - if (++prescale > PRESCALE_MAX)
> + if (++prescale > PRESCALE_MAX) {
> + dev_warn(chip->dev,
> + "%s: pwm[%d]: Prescale (=%lu) within max (=%d) for period=%d and duty cycle=%d is not achievable\n",
> + __func__, chan, prescale, PRESCALE_MAX,
> + period_ns, duty_ns);
> return -EINVAL;
> + }
> }
This extra debug output seems helpful but could you put it in its own
commit and keep this focused on fixing the instability you observed?
> + /*
> + * Clear trigger bit but set smooth bit to maintain old
> + * output.
> + */
> + value |= 1 << PWM_CONTROL_SMOOTH_SHIFT(chan);
> + value &= ~(1 << PWM_CONTROL_TRIGGER_SHIFT(chan));
> + writel(value, kp->base + PWM_CONTROL_OFFSET);
> +
The above lines are duplicated below. Perhaps a function is in order?
> + /* Set smooth type to 1 and disable */
> + value |= 1 << PWM_CONTROL_SMOOTH_SHIFT(chan);
> + value &= ~(1 << PWM_CONTROL_TRIGGER_SHIFT(chan));
> + writel(value, kp->base + PWM_CONTROL_OFFSET);
It seems like the important parts of the fix could be distilled down
to something like this:
diff --git a/drivers/pwm/pwm-bcm-kona.c b/drivers/pwm/pwm-bcm-kona.c
index 02bc048..4ff500c 100644
--- a/drivers/pwm/pwm-bcm-kona.c
+++ b/drivers/pwm/pwm-bcm-kona.c
@@ -76,7 +76,8 @@ static inline struct kona_pwmc *to_kona_pwmc(struct
pwm_chip *_chip)
return container_of(_chip, struct kona_pwmc, chip);
}
-static void kona_pwmc_apply_settings(struct kona_pwmc *kp, unsigned int chan)
+static void kona_pwmc_prepare_for_settings(struct kona_pwmc *kp,
+ unsigned int chan)
{
unsigned int value = readl(kp->base + PWM_CONTROL_OFFSET);
@@ -85,10 +86,19 @@ static void kona_pwmc_apply_settings(struct
kona_pwmc *kp, unsigned int chan)
value &= ~(1 << PWM_CONTROL_TRIGGER_SHIFT(chan));
writel(value, kp->base + PWM_CONTROL_OFFSET);
+ ndelay(400);
+}
+
+static void kona_pwmc_apply_settings(struct kona_pwmc *kp, unsigned int chan)
+{
+ unsigned int value = readl(kp->base + PWM_CONTROL_OFFSET);
+
/* Set trigger bit and clear smooth bit to apply new settings */
value &= ~(1 << PWM_CONTROL_SMOOTH_SHIFT(chan));
value |= 1 << PWM_CONTROL_TRIGGER_SHIFT(chan);
writel(value, kp->base + PWM_CONTROL_OFFSET);
+
+ ndelay(400);
}
static int kona_pwmc_config(struct pwm_chip *chip, struct pwm_device *pwm,
@@ -135,6 +145,8 @@ static int kona_pwmc_config(struct pwm_chip *chip,
struct pwm_device *pwm,
/* If the PWM channel is enabled, write the settings to the HW */
if (test_bit(PWMF_ENABLED, &pwm->flags)) {
+ kona_pwmc_prepare_for_settings(kp, chan);
+
value = readl(kp->base + PRESCALE_OFFSET);
value &= ~PRESCALE_MASK(chan);
value |= prescale << PRESCALE_SHIFT(chan);
@@ -164,6 +176,8 @@ static int kona_pwmc_set_polarity(struct pwm_chip
*chip, struct pwm_device *pwm,
return ret;
}
+ kona_pwmc_prepare_for_settings(kp, chan);
+
value = readl(kp->base + PWM_CONTROL_OFFSET);
if (polarity == PWM_POLARITY_NORMAL)
@@ -175,9 +189,6 @@ static int kona_pwmc_set_polarity(struct pwm_chip
*chip, struct pwm_device *pwm,
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;
@@ -209,12 +220,10 @@ static void kona_pwmc_disable(struct pwm_chip
*chip, struct pwm_device *pwm)
unsigned int chan = pwm->hwpwm;
/* Simulate a disable by configuring for zero duty */
+ kona_pwmc_prepare_for_settings(kp, chan);
writel(0, kp->base + DUTY_CYCLE_HIGH_OFFSET(chan));
kona_pwmc_apply_settings(kp, chan);
- /* Wait for waveform to settle before gating off the clock */
- ndelay(400);
-
clk_disable_unprepare(kp->clk);
}
--
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