Re: [PATCH v1 2/3] pwm: Add Allwinner's D1/T113-S3/R329 SoCs PWM support

Hello,

this isn't a complete review, just a first quick look. Up to you if you
follow up with a v2 fixing the things here. If you don't I will take a
deeper look at a later time.

On Thu, Jun 15, 2023 at 05:43:57PM +0300, Aleksandr Shubin wrote:

That is a detail that better fits into a code comment in the driver. The
user choosing if they should enable PWM_SUN20I or not, don't need to
know that.

Please add a "Limitations" section here answering the following
questions:

 - Is a currently running period completed when a new pwm_state is
   applied that has .enabled = true? What about .enabled = false?
 - How does the PWM behave when disabled? Typical behaviours are: drives
   to inactive level, just freezes or goes HIGH-Z.

Stick to the format that is used in other drivers to make this easily
grepable.

+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/pwm.h>
+#include <linux/clk.h>
+#include <linux/reset.h>

alphabetic ordering please

+#define PWM_CLK_CFG_REG(chan)		(0x20 + (((chan) >> 1) * 0x4))
+#define PWM_CLK_SRC			7
+#define PWM_CLK_SRC_MASK		GENMASK(8, PWM_CLK_SRC)
+#define PWM_CLK_DIV_M			0
+#define PWM_CLK_DIV_M_MASK		GENMASK(3, PWM_CLK_DIV_M)
+
+#define PWM_CLK_GATE_REG		0x40
+#define PWM_CLK_GATING(chan)		BIT(chan)
+
+#define PWM_ENABLE_REG			0x80
+#define PWM_EN(chan)			BIT(chan)
+
+#define PWM_CTL_REG(chan)		(0x100 + (chan) * 0x20)
+#define PWM_ACT_STA			BIT(8)
+#define PWM_PRESCAL_K			0
+#define PWM_PRESCAL_K_MASK		GENMASK(7, PWM_PRESCAL_K)
+
+#define PWM_PERIOD_REG(chan)		(0x104 + (chan) * 0x20)
+#define PWM_ENTIRE_CYCLE		16
+#define PWM_ENTIRE_CYCLE_MASK		GENMASK(31, PWM_ENTIRE_CYCLE)
+#define PWM_ACT_CYCLE			0
+#define PWM_ACT_CYCLE_MASK		GENMASK(15, PWM_ACT_CYCLE)
+
+#define SET_VALUE(reg_val, val, name) \
+		 (reg_val = (((reg_val) & ~name##_MASK) | ((val) << (name))))
+#define GET_VALUE(reg_val, name) \
+		 (((reg_val) & ~name##_MASK) >> (name))

Please use FIELD_GET here instead. This works nice with dropping
PWM_PRESCAL_K and renaming PWM_PRESCAL_K_MASK to PWM_PRESCAL_K.

[...]
+static int sun20i_pwm_get_state(struct pwm_chip *chip,
+				struct pwm_device *pwm,
+				struct pwm_state *state)
+{
+	struct sun20i_pwm_chip *sun20i_chip = to_sun20i_pwm_chip(chip);
+	u64 clk_rate, tmp;
+	u32 val;
+	u16 clk_div, act_cycle;
+	u8 prescal, div_id;
+	u8 chn = pwm->hwpwm;
+
+	mutex_lock(&sun20i_chip->mutex);
+
+	val = sun20i_pwm_readl(sun20i_chip, PWM_CLK_CFG_REG(pwm->hwpwm));
+	div_id = GET_VALUE(val, PWM_CLK_DIV_M);
+	if (GET_VALUE(val, PWM_CLK_SRC) == 0)
+		clk_rate = clk_get_rate(sun20i_chip->clk_hosc);
+	else
+		clk_rate = clk_get_rate(sun20i_chip->clk_bus);
+
+	val = sun20i_pwm_readl(sun20i_chip, PWM_CTL_REG(pwm->hwpwm));
+	if (PWM_ACT_STA & val)
+		state->polarity = PWM_POLARITY_NORMAL;
+	else
+		state->polarity = PWM_POLARITY_INVERSED;
+
+	prescal = PWM_PRESCAL_K & val;
+
+	val = sun20i_pwm_readl(sun20i_chip, PWM_ENABLE_REG);
+	if (PWM_EN(chn) & val)
+		state->enabled = true;
+	else
+		state->enabled = false;
+
+	val = sun20i_pwm_readl(sun20i_chip, PWM_PERIOD_REG(pwm->hwpwm));
+	act_cycle = GET_VALUE(val, PWM_ACT_CYCLE);
+	clk_div = GET_VALUE(val, PWM_ENTIRE_CYCLE);
+
+	tmp = act_cycle * prescal * (1U << div_id) * NSEC_PER_SEC;
+	state->duty_cycle = DIV_ROUND_CLOSEST_ULL(tmp, clk_rate);
+	tmp = clk_div * prescal * (1U << div_id) * NSEC_PER_SEC;
+	state->period = DIV_ROUND_CLOSEST_ULL(tmp, clk_rate);

You have to use ROUND_UP here to make

	.get_state(mypwm, &state);
	.apply(mypwm, &state);

idempotent. Test your driver with PWM_DEBUG enabled. With an appropriate
test sequence this should tell you such things. Test with something
like:

	for i in some_range:
		pwm_apply_state(mypwm, { .enabled = true, .period = i, .duty_cycle = 0 })
	for i in reversed(some_range):
		pwm_apply_state(mypwm, { .enabled = true, .period = i, .duty_cycle = 0 })

	for i in [0, someperiod]:
		pwm_apply_state(mypwm, { .enabled = true, .period = someperiod, .duty_cycle = i })
	for i in reversed([0, someperiod]):
		pwm_apply_state(mypwm, { .enabled = true, .period = someperiod, .duty_cycle = i })

+	mutex_unlock(&sun20i_chip->mutex);
+
+	return 0;
+}
+
+static int sun20i_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
+			    const struct pwm_state *state)
+{
+	struct pwm_state curstate;
+	int ret = 0;
+	u32 clk_gate, clk_cfg, pwm_en, ctl, period;
+	u64 bus_rate, hosc_rate, clk_div, val, clk_rate;
+	u16 prescaler, div_m;
+	bool use_bus_clk;
+	struct sun20i_pwm_chip *sun20i_chip = to_sun20i_pwm_chip(chip);
+
+	mutex_lock(&sun20i_chip->mutex);
+	pwm_get_state(pwm, &curstate);

Don't call pwm API functions in lowlevel driver. Even less while holding
a lock. If you need the previous state, using pwm->state is fine.

+	pwm_en = sun20i_pwm_readl(sun20i_chip, PWM_ENABLE_REG);
+	if (state->polarity != curstate.polarity ||
+	    state->duty_cycle != curstate.duty_cycle ||
+	    state->period != curstate.period) {
+		ctl = sun20i_pwm_readl(sun20i_chip, PWM_CTL_REG(pwm->hwpwm));
+		clk_cfg = sun20i_pwm_readl(sun20i_chip, PWM_CLK_CFG_REG(pwm->hwpwm));
+		hosc_rate = clk_get_rate(sun20i_chip->clk_hosc);
+		bus_rate = clk_get_rate(sun20i_chip->clk_bus);
+
+		if (pwm_en & PWM_EN(pwm->hwpwm ^ 1)) {
+			/* check period only */
+			if (GET_VALUE(clk_cfg, PWM_CLK_SRC) == 0)
+				clk_rate = hosc_rate;
+			else
+				clk_rate = bus_rate;
+
+			val = state->period * clk_rate;

This might overflow.

+			do_div(val, NSEC_PER_SEC);
+
+			div_m = GET_VALUE(clk_cfg, PWM_CLK_DIV_M);
+
+			/* calculate and set prescaler, PWM entire cycle */
+			clk_div = val;
+			for (prescaler = 0; clk_div > 65535; prescaler++) {
+				if (prescaler >= 256) {
+					dev_err(sun20i_chip->chip.dev, "Period is too long\n");

dev_err in .apply() isn't a good idea. Please fail silently.

Also you should configure the biggest period the hardware can support
that isn't bigger than state->period. So the requested period cannot be
too long.

+					ret = -EINVAL;
+					goto unlock_mutex;
+				}
+
+				clk_div = val;
+				do_div(clk_div, 1U << div_m);

This can be simplified to clk_div >> div_m.

+				do_div(clk_div, prescaler + 1);
+			}

I wonder if prescaler can be calculated without a loop.

+		} else {
+			/* check period and select clock source */
+			use_bus_clk = false;
+			val = state->period * hosc_rate;
+			do_div(val, NSEC_PER_SEC);
+			if (val <= 1) {
+				use_bus_clk = true;
+				val = state->period * bus_rate;
+				do_div(val, NSEC_PER_SEC);
+				if (val <= 1) {
+					dev_err(sun20i_chip->chip.dev, "Period is too small\n");
+					ret = -EINVAL;
+					goto unlock_mutex;
+				}
+			}
+
+			if (use_bus_clk)
+				SET_VALUE(clk_cfg, 1, PWM_CLK_SRC);
+			else
+				SET_VALUE(clk_cfg, 0, PWM_CLK_SRC);
+
+			/* calculate and set prescaler, M factor, PWM entire cycle */
+			clk_div = val;
+			for (prescaler = div_m = 0; clk_div > 65535; prescaler++) {
+				if (prescaler >= 256) {
+					prescaler = 0;
+					div_m++;
+					if (div_m >= 9) {
+						dev_err(sun20i_chip->chip.dev, "Period is too long\n");
+						ret = -EINVAL;
+						goto unlock_mutex;
+					}
+				}
+
+				clk_div = val;
+				do_div(clk_div, 1U << div_m);
+				do_div(clk_div, prescaler + 1);
+			}
+
+			/* set up the M factor */
+			SET_VALUE(clk_cfg, div_m, PWM_CLK_DIV_M);
+
+			sun20i_pwm_writel(sun20i_chip, clk_cfg, PWM_CLK_CFG_REG(pwm->hwpwm));
+		}
+
+		period = sun20i_pwm_readl(sun20i_chip, PWM_PERIOD_REG(pwm->hwpwm));
+
+		SET_VALUE(period, clk_div, PWM_ENTIRE_CYCLE);
+		SET_VALUE(ctl, prescaler, PWM_PRESCAL_K);

Are there any fields in PWM_PERIOD_REG(pwm->hwpwm) you're not
recalculating? If not, you can skip reading the register and use
FIELD_PREP instead of SET_VALUE.

+
+		/* set duty cycle */
+		val = state->period;
+		do_div(val, clk_div);
+		clk_div = state->duty_cycle;
+		do_div(clk_div, val);
+		if (clk_div > 65535)
+			clk_div = 65535;
+
+		SET_VALUE(period, clk_div, PWM_ACT_CYCLE);
+		sun20i_pwm_writel(sun20i_chip, period, PWM_PERIOD_REG(pwm->hwpwm));
+
+		if (state->polarity == PWM_POLARITY_NORMAL)
+			ctl |= PWM_ACT_STA;
+		else
+			ctl &= ~PWM_ACT_STA;
+
+		sun20i_pwm_writel(sun20i_chip, ctl, PWM_CTL_REG(pwm->hwpwm));
+	}
+
+	if (state->enabled != curstate.enabled) {
+		clk_gate = sun20i_pwm_readl(sun20i_chip, PWM_CLK_GATE_REG);
+
+		if (state->enabled) {
+			clk_gate |= PWM_CLK_GATING(pwm->hwpwm);
+			pwm_en |= PWM_EN(pwm->hwpwm);
+		} else {
+			clk_gate &= ~PWM_CLK_GATING(pwm->hwpwm);
+			pwm_en &= ~PWM_EN(pwm->hwpwm);
+		}

Disabling (probably) needs to be handled earlier. Consider your PWM is
enabled with say .period = 5000 and .duty_cycle = 0. If now

	pwm_apply_state(&mypwm, &(struct pwm_state){ .period = 5000, .duty_cycle = 5000, .enabled = false })

is called, the output might become active before gating becomes
effective. It's not always possible to prevent such spikes, but if it
is, please do.

+		sun20i_pwm_writel(sun20i_chip, pwm_en, PWM_ENABLE_REG);
+		sun20i_pwm_writel(sun20i_chip, clk_gate, PWM_CLK_GATE_REG);
+	}
+
+unlock_mutex:
+	mutex_unlock(&sun20i_chip->mutex);
+
+	return ret;
+}
[...]
+static int sun20i_pwm_probe(struct platform_device *pdev)
+{
+	struct sun20i_pwm_chip *sun20i_chip;
+	int ret;
+
+	sun20i_chip = devm_kzalloc(&pdev->dev, sizeof(*sun20i_chip), GFP_KERNEL);
+	if (!sun20i_chip)
+		return -ENOMEM;
+
+	sun20i_chip->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(sun20i_chip->base))
+		return PTR_ERR(sun20i_chip->base);
+
+	sun20i_chip->clk_bus = devm_clk_get(&pdev->dev, "bus");

consider using devm_clk_get_enabled()

+	if (IS_ERR(sun20i_chip->clk_bus)) {
+		dev_err(&pdev->dev, "Failed to get bus clock\n");
+		return PTR_ERR(sun20i_chip->clk_bus);

Please make this:

	return dev_err_probe(&pdev->dev, PTR_ERR(sun20i_chip->clk_bus),
			     "Failed to get bus clock\n");

ditto for the other error paths.

+	}
+
+	sun20i_chip->clk_hosc = devm_clk_get(&pdev->dev, "hosc");
+	if (IS_ERR(sun20i_chip->clk_hosc)) {
+		dev_err(&pdev->dev, "Failed to get hosc clock\n");
+		return PTR_ERR(sun20i_chip->clk_hosc);
+	}
+
+	sun20i_chip->rst = devm_reset_control_get(&pdev->dev, NULL);
+	if (IS_ERR(sun20i_chip->rst)) {
+		dev_err(&pdev->dev, "Failed to get bus reset\n");
+		return PTR_ERR(sun20i_chip->rst);
+	}
+
+	/* Deassert reset */
+	ret = reset_control_deassert(sun20i_chip->rst);
+	if (ret) {
+		dev_err(&pdev->dev, "Failed to deassert reset\n");
+		return ret;
+	}
+
+	ret = clk_prepare_enable(sun20i_chip->clk_bus);
+	if (ret) {
+		dev_err(&pdev->dev, "Failed to ungate bus clock\n");
+		goto err_bus;
+	}
+
+	ret = of_property_read_u32(pdev->dev.of_node,
+				   "allwinner,pwm-channels",
+				   &sun20i_chip->chip.npwm);
+	if (ret) {
+		dev_err(&pdev->dev, "Can't get pwm-channels\n");
+		goto err_pwm_add;
+	}
+
+	sun20i_chip->chip.dev = &pdev->dev;
+	sun20i_chip->chip.ops = &sun20i_pwm_ops;
+
+	mutex_init(&sun20i_chip->mutex);

If the hardware is enabled, please make sure that the needed clocks are
not disabled.

+	ret = pwmchip_add(&sun20i_chip->chip);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "Failed to add PWM chip: %d\n", ret);
+		goto err_pwm_add;
+	}
+
+	platform_set_drvdata(pdev, sun20i_chip);
+
+	return 0;
+
+err_pwm_add:
+	clk_disable_unprepare(sun20i_chip->clk_bus);
+err_bus:
+	reset_control_assert(sun20i_chip->rst);
+	return ret;
+}

Best regards
Uwe

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