Re: [v4 2/2] pwm: Add Aspeed ast2600 PWM support

Hello,

On Mon, May 10, 2021 at 03:35:11PM +0800, Billy Tsai wrote:

Does that mean it doesn't support earlier versions of the IP?

+ *
+ * The formula of pwm frequency:
+ * PWM frequency = CLK Source / ((DIV_L + 1) * BIT(DIV_H) * (PERIOD + 1))
+ *
+ * The software driver fixes the period to 256, which causes the high-frequency
+ * precision of the PWM to be coarse, in exchange for the fineness of the duty cycle.
+ *
+ * Register usage:
+ * PIN_ENABLE: When it is unset the pwm controller will always output low to the extern.
+ * Use to determin PWM channel enable/disable.

s/determin PWM channel enable.disable/determine if the PWM channel is enabled or disabled/

+ * CLK_ENABLE: When it is unset the pwm controller will reset the duty counter to 0 and
+ * output low to the PIN_ENABLE mux after that the driver can still change the pwm period
+ * and duty and the value will apply when CLK_ENABLE be set again.
+ * Use to determin whether duty_cycle bigger than 0.
+ * PWM_ASPEED_INVERSE: When it is toggled the output value will inverse immediately.
+ *
+ * Limitations:
+ * - When changing both duty cycle and period, we cannot prevent in
+ *   software that the output might produce a period with mixed
+ *   settings.
+ *
+ * Improvements:
+ * - When changing the duty cycle or period, our pwm controller will not
+ *   generate the glitch, the configure will change at next cycle of pwm.
+ *   This improvement can disable/enable through PWM_ASPEED_DUTY_SYNC_DISABLE.
+ */
+
+#include <linux/clk.h>
+#include <linux/errno.h>
+#include <linux/delay.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/of_platform.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/sysfs.h>
+#include <linux/reset.h>
+#include <linux/regmap.h>
+#include <linux/bitfield.h>
+#include <linux/slab.h>
+#include <linux/pwm.h>
+
+/* The channel number of Aspeed pwm controller */
+#define PWM_ASPEED_NR_PWMS 16
+
+/* PWM Control Register */
+#define PWM_ASPEED_CTRL_CH(ch) (((ch * 0x10) + 0x00))

Please put ch in parenthesis.

+#define PWM_ASPEED_LOAD_SEL_RISING_AS_WDT BIT(19)
+#define PWM_ASPEED_DUTY_LOAD_AS_WDT_ENABLE BIT(18)
+#define PWM_ASPEED_DUTY_SYNC_DISABLE BIT(17)
+#define PWM_ASPEED_CLK_ENABLE BIT(16)
+#define PWM_ASPEED_LEVEL_OUTPUT BIT(15)
+#define PWM_ASPEED_INVERSE BIT(14)
+#define PWM_ASPEED_OPEN_DRAIN_ENABLE BIT(13)
+#define PWM_ASPEED_PIN_ENABLE BIT(12)
+#define PWM_ASPEED_CLK_DIV_H GENMASK(11, 8)
+#define PWM_ASPEED_CLK_DIV_L GENMASK(7, 0)

It would be great if the bit definitions contained the name of the
register. This simplifies verifying that we're using a define for the
expected register.

+/* PWM Duty Cycle Register */
+#define PWM_ASPEED_DUTY_CYCLE_CH(ch) (((ch * 0x10) + 0x04))
+#define PWM_ASPEED_PERIOD GENMASK(31, 24)
+#define PWM_ASPEED_POINT_AS_WDT GENMASK(23, 16)
+#define PWM_ASPEED_FALLING_POINT GENMASK(15, 8)
+#define PWM_ASPEED_RISING_POINT GENMASK(7, 0)
+
+/* PWM fixed value */
+#define PWM_ASPEED_FIXED_PERIOD 0xff
+
+struct aspeed_pwm_data {
+	struct pwm_chip chip;
+	struct clk *clk;
+	struct regmap *regmap;
+	struct reset_control *reset;
+};
+
+static inline struct aspeed_pwm_data *
+aspeed_pwm_chip_to_data(struct pwm_chip *c)
+{
+	return container_of(c, struct aspeed_pwm_data, chip);
+}
+
+static void aspeed_set_pwm_clk_enable(struct regmap *regmap, u8 pwm_channel,
+					  bool enable)

I'd call this function aspeed_pwm_set_clk_enable to use "aspeed_pwm_" as
the common prefix for all functions. Similarly for the other functions.

+{
+	regmap_update_bits(regmap, PWM_ASPEED_CTRL_CH(pwm_channel),
+			   PWM_ASPEED_CLK_ENABLE,
+			   enable ? PWM_ASPEED_CLK_ENABLE : 0);

There is only a single caller for this function, I'd recommend to fold
it into this caller.

+}
+
+static u32 apseed_get_pwm_freq(struct pwm_chip *chip, struct pwm_device *pwm)
+{
+	struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
+	unsigned long rate;
+	u32 index = pwm->hwpwm;
+	u32 div_h, div_l, cur_freq, val;
+
+	rate = clk_get_rate(priv->clk);
+	regmap_read(priv->regmap, PWM_ASPEED_CTRL_CH(index), &val);
+	div_h = FIELD_GET(PWM_ASPEED_CLK_DIV_H, val);
+	div_l = FIELD_GET(PWM_ASPEED_CLK_DIV_L, val);
+
+	cur_freq = DIV_ROUND_DOWN_ULL(rate, (BIT(div_h) * (div_l + 1) *
+					     (PWM_ASPEED_FIXED_PERIOD + 1)));
+	return cur_freq;
+}
+
+static int aspeed_set_pwm_freq(struct pwm_chip *chip, struct pwm_device *pwm,
+			       const struct pwm_state *state)
+{
+	struct device *dev = chip->dev;
+	struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
+	unsigned long rate;
+	u32 div_h, div_l, freq;
+	u32 index = pwm->hwpwm;
+	/* Get the smallest value for div_h  */
+	freq = DIV_ROUND_UP_ULL(NSEC_PER_SEC, state->period);
+	rate = clk_get_rate(priv->clk);
+	div_h = DIV_ROUND_DOWN_ULL(rate,
+				   ((FIELD_MAX(PWM_ASPEED_CLK_DIV_L) + 1) *
+				    freq * (PWM_ASPEED_FIXED_PERIOD + 1)));

Please don't divide by the result of a division.

+	div_h = order_base_2(div_h);
+	if (div_h > 0xf)
+		div_h = 0xf;
+
+	div_l = DIV_ROUND_DOWN_ULL(rate >> div_h,
+				   (freq * (PWM_ASPEED_FIXED_PERIOD + 1)));
+	if (div_l == 0) {
+		dev_err(dev, "Period too small, cannot implement it");
+		return -ERANGE;
+	}
+
+	div_l -= 1;
+
+	if (div_l > 255)
+		div_l = 255;
+
+	dev_dbg(dev, "clk source: %ld div h %x, l : %x\n", rate, div_h, div_l);
+
+	regmap_update_bits(priv->regmap, PWM_ASPEED_CTRL_CH(index),
+			   (PWM_ASPEED_CLK_DIV_H | PWM_ASPEED_CLK_DIV_L),
+			   FIELD_PREP(PWM_ASPEED_CLK_DIV_H, div_h) |
+				   FIELD_PREP(PWM_ASPEED_CLK_DIV_L, div_l));
+	return 0;
+}
+
+static void aspeed_set_pwm_duty(struct pwm_chip *chip, struct pwm_device *pwm,
+				const struct pwm_state *state)
+{
+	struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
+	u32 duty_pt;
+	u32 index = pwm->hwpwm;
+	u32 cur_freq;
+	u64 cur_period;
+
+	cur_freq = apseed_get_pwm_freq(chip, pwm);

s/apseed/aspeed/

cur_freq is the result of a division ...

+	cur_period = DIV_ROUND_DOWN_ULL(NSEC_PER_SEC, cur_freq);

... dividing through such a number loses precision.

+	duty_pt = DIV_ROUND_DOWN_ULL(
+		state->duty_cycle * (PWM_ASPEED_FIXED_PERIOD + 1), cur_period);
+	if (duty_pt == 0) {
+		aspeed_set_pwm_clk_enable(priv->regmap, index, false);
+	} else {
+		if (duty_pt >= (PWM_ASPEED_FIXED_PERIOD + 1))
+			duty_pt = 0;
+		/* When duty_pt = 0 it mean our duty cycle = 100% */

Please put this comment above the code that it explains.

+		regmap_update_bits(
+			priv->regmap, PWM_ASPEED_DUTY_CYCLE_CH(index),
+			PWM_ASPEED_FALLING_POINT,
+			FIELD_PREP(PWM_ASPEED_FALLING_POINT, duty_pt));
+		aspeed_set_pwm_clk_enable(priv->regmap, index, true);
+	}
+}
+
+static void aspeed_set_pwm_polarity(struct pwm_chip *chip,
+				    struct pwm_device *pwm,
+				    const struct pwm_state *state)
+{
+	struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
+	u32 index = pwm->hwpwm;
+
+	regmap_update_bits(priv->regmap, PWM_ASPEED_CTRL_CH(index),
+			   PWM_ASPEED_INVERSE,
+			   FIELD_PREP(PWM_ASPEED_INVERSE, state->polarity));
+}

This function also only has a single caller and can better be folded
into it.

+static void aspeed_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
+				 struct pwm_state *state)
+{
+	struct device *dev = chip->dev;
+	struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
+	u32 index = pwm->hwpwm;
+	bool polarity, ch_en, clk_en;
+	u32 duty_pt, val;
+	u32 cur_freq;
+
+	regmap_read(priv->regmap, PWM_ASPEED_CTRL_CH(index), &val);
+	polarity = FIELD_GET(PWM_ASPEED_INVERSE, val);
+	ch_en = FIELD_GET(PWM_ASPEED_PIN_ENABLE, val);
+	clk_en = FIELD_GET(PWM_ASPEED_CLK_ENABLE, val);
+	regmap_read(priv->regmap, PWM_ASPEED_DUTY_CYCLE_CH(index), &val);
+	duty_pt = FIELD_GET(PWM_ASPEED_FALLING_POINT, val);
+
+	cur_freq = apseed_get_pwm_freq(chip, pwm);
+
+	state->period = DIV_ROUND_DOWN_ULL(NSEC_PER_SEC, cur_freq);

Please round up in .get_state().

+	if (clk_en && duty_pt)
+		state->duty_cycle = DIV_ROUND_DOWN_ULL(
+			state->period * duty_pt, PWM_ASPEED_FIXED_PERIOD + 1);
+	else
+		state->duty_cycle = clk_en ? state->period : 0;
+	state->polarity = polarity;
+	state->enabled = ch_en;
+	dev_dbg(dev, "get period: %lldns, duty_cycle: %lldns", state->period,
+		state->duty_cycle);
+}
+
+static int aspeed_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
+			    const struct pwm_state *state)
+{
+	struct device *dev = chip->dev;
+	struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
+	u32 index = pwm->hwpwm;
+	struct pwm_state cur_state;
+	int ret;
+
+	aspeed_pwm_get_state(chip, pwm, &cur_state);
+	dev_dbg(dev, "cur period: %lldns, cur duty_cycle: %lldns",
+		cur_state.period, cur_state.duty_cycle);
+	dev_dbg(dev, "apply period: %lldns, duty_cycle: %lldns", state->period,
+		state->duty_cycle);
+	regmap_update_bits(priv->regmap, PWM_ASPEED_CTRL_CH(index),
+			   PWM_ASPEED_PIN_ENABLE,
+			   state->enabled ? PWM_ASPEED_PIN_ENABLE : 0);
+	if (cur_state.period != state->period) {
+		ret = aspeed_set_pwm_freq(chip, pwm, state);
+		if (ret)
+			return ret;
+		aspeed_set_pwm_duty(chip, pwm, state);
+	} else if (cur_state.duty_cycle != state->duty_cycle)
+		aspeed_set_pwm_duty(chip, pwm, state);

In aspeed_set_pwm_duty() you call apseed_get_pwm_freq(), in one of the two
cases above you already know the freq. If you ask me, just drop the
cur_state.period != state->period check and calculate all the required
settings unconditionally. Then you also don't need to call
aspeed_pwm_get_state(). (Apart from that apseed_get_pwm_freq implements
the wrong rounding for .apply().)

+	aspeed_set_pwm_polarity(chip, pwm, state);
+	return 0;
+}
+
+static const struct pwm_ops aspeed_pwm_ops = {
+	.apply = aspeed_pwm_apply,
+	.get_state = aspeed_pwm_get_state,
+	.owner = THIS_MODULE,
+};
+
+static int aspeed_pwm_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	int ret, index;
+	struct aspeed_pwm_data *priv;
+	struct device_node *np;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	np = pdev->dev.parent->of_node;
+	if (!of_device_is_compatible(np, "aspeed,ast2600-pwm-tach")) {
+		dev_err(dev, "unsupported pwm device binding\n");
+		return -ENODEV;
+	}
+
+	priv->regmap = syscon_node_to_regmap(np);
+	if (IS_ERR(priv->regmap)) {
+		dev_err(dev, "Couldn't get regmap\n");
+		return -ENODEV;

Please return PTR_ERR(priv->regmap) here and use dev_err_probe for
consistency.

+	}
+
+	priv->clk = of_clk_get(np, 0);

Maybe use devm_clk_get() instead? (Otherwise you have to put the clock
in the error paths.)

+	if (IS_ERR(priv->clk))
+		return dev_err_probe(dev, PTR_ERR(priv->clk),
+				     "get clock failed\n");
+
+	ret = clk_prepare_enable(priv->clk);
+	if (ret) {
+		dev_err(dev, "couldn't enable clock\n");
+		return ret;
+	}
+
+	priv->reset = of_reset_control_get_shared(np, NULL);
+	if (IS_ERR(priv->reset))
+		return dev_err_probe(dev, PTR_ERR(priv->reset),
+				     "get reset failed\n");
+
+	ret = reset_control_deassert(priv->reset);
+	if (ret) {
+		dev_err(dev, "cannot deassert reset control: %pe\n",
+			ERR_PTR(ret));
+		clk_disable_unprepare(priv->clk);

Consider using goto for error handling. Then you don't have to repeat
the same thing over and over again.

+		return ret;
+	}
+
+	priv->chip.dev = dev;
+	priv->chip.ops = &aspeed_pwm_ops;
+	priv->chip.npwm = PWM_ASPEED_NR_PWMS;
+	priv->chip.of_xlate = of_pwm_xlate_with_flags;
+	priv->chip.of_pwm_n_cells = 3;
+
+	/*
+	 * Fixed the period to the max value and rising point to 0
+	 * for high resolution and simplified frequency calculation.

There is a stray non-printable char before "simplified".

+	 */
+	for (index = 0; index < PWM_ASPEED_NR_PWMS; index++) {
+		regmap_update_bits(
+			priv->regmap, PWM_ASPEED_DUTY_CYCLE_CH(index),
+			PWM_ASPEED_PERIOD,
+			FIELD_PREP(PWM_ASPEED_PERIOD, PWM_ASPEED_FIXED_PERIOD));
+		regmap_update_bits(priv->regmap,
+				   PWM_ASPEED_DUTY_CYCLE_CH(index),
+				   PWM_ASPEED_RISING_POINT, 0);
+	}

Please don't modify the output in .probe. .apply is the only function
that is supposed to do that.

+
+	ret = pwmchip_add(&priv->chip);
+	if (ret < 0) {
+		dev_err(dev, "failed to add PWM chip: %pe\n", ERR_PTR(ret));
+		reset_control_assert(priv->reset);
+		clk_disable_unprepare(priv->clk);
+		return ret;
+	}
+	dev_set_drvdata(dev, priv);
+	return ret;

s/ret/0/

+}
+
+static int aspeed_pwm_remove(struct platform_device *dev)
+{
+	struct aspeed_pwm_data *priv = platform_get_drvdata(dev);
+
+	pwmchip_remove(&priv->chip);
+	reset_control_assert(priv->reset);
+	clk_disable_unprepare(priv->clk);
+
+	return 0;
+}
+
+static const struct of_device_id of_pwm_match_table[] = {
+	{
+		.compatible = "aspeed,ast2600-pwm",
+	},
+	{},
+};
+MODULE_DEVICE_TABLE(of, of_pwm_match_table);
+
+static struct platform_driver aspeed_pwm_driver = {
+	.probe		= aspeed_pwm_probe,
+	.remove		= aspeed_pwm_remove,
+	.driver		= {
+		.name	= "aspeed_pwm",
+		.of_match_table = of_pwm_match_table,
+	},
+};

Please use alignment of = consistently. Either don't do it at all (my
favourite) or do it for all structs in the same way.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |