Re: [PATCH 2/2] pwm: sifive: Add a driver for SiFive SoC PWM

Uwe Kleine-König
2019-01-15T22:00:46Z

Hello,

On Fri, Jan 11, 2019 at 01:52:44PM +0530, Yash Shah wrote:
> Adds a PWM driver for PWM chip present in SiFive's HiFive Unleashed SoC.
>
> Signed-off-by: Wesley W. Terpstra <wesley@sifive.com>
> [Atish: Various fixes and code cleanup]
> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> Signed-off-by: Yash Shah <yash.shah@sifive.com>
> ---
> drivers/pwm/Kconfig | 10 ++
> drivers/pwm/Makefile | 1 +
> drivers/pwm/pwm-sifive.c | 246 +++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 257 insertions(+)
> create mode 100644 drivers/pwm/pwm-sifive.c
>
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index a8f47df..3bcaf6a 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -380,6 +380,16 @@ config PWM_SAMSUNG
> To compile this driver as a module, choose M here: the module
> will be called pwm-samsung.
>
> +config PWM_SIFIVE
> + tristate "SiFive PWM support"
> + depends on OF
> + depends on COMMON_CLK

I'd say add:

depends on MACH_SIFIVE || COMPILE_TEST

(I guess "MACH_SIFIVE" is wrong, but I assume you get what I mean.)

> + help
> + Generic PWM framework driver for SiFive SoCs.
> +
> + To compile this driver as a module, choose M here: the module
> + will be called pwm-sifive.
> +
> config PWM_SPEAR
> tristate "STMicroelectronics SPEAr PWM support"
> depends on PLAT_SPEAR
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index 9c676a0..30089ca 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -37,6 +37,7 @@ obj-$(CONFIG_PWM_RCAR) += pwm-rcar.o
> obj-$(CONFIG_PWM_RENESAS_TPU) += pwm-renesas-tpu.o
> obj-$(CONFIG_PWM_ROCKCHIP) += pwm-rockchip.o
> obj-$(CONFIG_PWM_SAMSUNG) += pwm-samsung.o
> +obj-$(CONFIG_PWM_SIFIVE) += pwm-sifive.o
> obj-$(CONFIG_PWM_SPEAR) += pwm-spear.o
> obj-$(CONFIG_PWM_STI) += pwm-sti.o
> obj-$(CONFIG_PWM_STM32) += pwm-stm32.o
> diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
> new file mode 100644
> index 0000000..7fee809
> --- /dev/null
> +++ b/drivers/pwm/pwm-sifive.c
> @@ -0,0 +1,246 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2017-2018 SiFive
> + * For SiFive's PWM IP block documentation please refer Chapter 14 of
> + * Reference Manual : https://static.dev.sifive.com/FU540-C000-v1.0.pdf

I wonder if such an instance should be only a single PWM instead of
four. Then you were more flexible with the period lengths (using
pwmcfg.pwmzerocmp) and could do stuff like inverted and uninverted mode.

I didn't understand how the deglitch logic works yet. Currently it is
not used which might result in four edges in a single period (which is
bad).

> + */
> +#include <linux/clk.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/slab.h>
> +
> +/* Register offsets */
> +#define REG_PWMCFG 0x0
> +#define REG_PWMCOUNT 0x8
> +#define REG_PWMS 0x10
> +#define REG_PWMCMP0 0x20

I suggest a common prefix for these defines. Something like
PWM_SIFIVE_

> +
> +/* PWMCFG fields */
> +#define BIT_PWM_SCALE 0
> +#define BIT_PWM_STICKY 8
> +#define BIT_PWM_ZERO_ZMP 9

the manual calls this "pwmzerocmp".

> +#define BIT_PWM_DEGLITCH 10
> +#define BIT_PWM_EN_ALWAYS 12
> +#define BIT_PWM_EN_ONCE 13
> +#define BIT_PWM0_CENTER 16
> +#define BIT_PWM0_GANG 24
> +#define BIT_PWM0_IP 28

Also a common prefix please. Something like PWM_SIFIVE_PWMCFG_ seems
sensible.

> +#define SIZE_PWMCMP 4

Please describe what this constant means. I think this is "ncmp" in the
reference manual. If so, using PWM_SIFIVE_NCMP as name instead seems
adequate.

> +#define MASK_PWM_SCALE 0xf

MASK_PWM_SCALE is unused, please drop it.

> +struct sifive_pwm_device {
> + struct pwm_chip chip;
> + struct notifier_block notifier;
> + struct clk *clk;
> + void __iomem *regs;
> + unsigned int approx_period;
> + unsigned int real_period;
> +};

I'd call this pwm_sifive_ddata. The prefix because the driver is called
pwm-sifive and ddata because this is driver data and not a device.

> +static inline struct sifive_pwm_device *to_sifive_pwm_chip(struct pwm_chip *c)
> +{
> + return container_of(c, struct sifive_pwm_device, chip);
> +}
> +
> +static void sifive_pwm_get_state(struct pwm_chip *chip, struct pwm_device *dev,
> + struct pwm_state *state)

given that the driver is called pwm-sifive, please use pwm_sifive as
function prefix.

> +{
> + struct sifive_pwm_device *pwm = to_sifive_pwm_chip(chip);
> + u32 duty;
> +
> + duty = readl(pwm->regs + REG_PWMCMP0 + dev->hwpwm * SIZE_PWMCMP);
> +
> + state->period = pwm->real_period;
> + state->duty_cycle = ((u64)duty * pwm->real_period) >> 16;

In the reference manual this 16 is called "cmpwidth" I think. If I
understand correctly this might in theory be different from 16, so it
would be great if this would be at least a cpp symbol for now.

> + state->polarity = PWM_POLARITY_INVERSED;
> + state->enabled = duty > 0;
> +}
> +
> +static int sifive_pwm_apply(struct pwm_chip *chip, struct pwm_device *dev,
> + struct pwm_state *state)
> +{
> + struct sifive_pwm_device *pwm = to_sifive_pwm_chip(chip);
> + unsigned int duty_cycle;
> + u32 frac;
> +
> + if (state->polarity != PWM_POLARITY_INVERSED)
> + return -EINVAL;
> +
> + duty_cycle = state->duty_cycle;
> + if (!state->enabled)
> + duty_cycle = 0;
> +
> + frac = div_u64((u64)duty_cycle << 16, state->period);
> + frac = min(frac, 0xFFFFU);

In the previous review round I asked here:

| Also if real_period is for example 10 ms and the consumer requests
| duty=12 ms + period=100 ms, the hardware is configured for duty=1.2 ms +
| period=10 ms, right?

which you confirmed. IMHO this is not acceptable. If the period is
fixed, you should return -EINVAL (I think) if a different period is
requested.

> + writel(frac, pwm->regs + REG_PWMCMP0 + dev->hwpwm * SIZE_PWMCMP);

If you get a constant inactive output with frac=0 and a constant active
output with frac=0xffff the calculation above seems wrong to me.
(A value i written to the pwmcmpX register means a duty cycle of
(i * period / 0xffff). Your calculation assumes a divisor of 0x10000
however.)

> +
> + if (state->enabled)
> + sifive_pwm_get_state(chip, dev, state);

@Thierry: Should we bless this correction of state?

> +
> + return 0;
> +}
> +
> +static const struct pwm_ops sifive_pwm_ops = {
> + .get_state = sifive_pwm_get_state,
> + .apply = sifive_pwm_apply,
> + .owner = THIS_MODULE,
> +};
> +
> +static struct pwm_device *sifive_pwm_xlate(struct pwm_chip *chip,
> + const struct of_phandle_args *args)
> +{
> + struct sifive_pwm_device *pwm = to_sifive_pwm_chip(chip);
> + struct pwm_device *dev;
> +
> + if (args->args[0] >= chip->npwm)
> + return ERR_PTR(-EINVAL);
> +
> + dev = pwm_request_from_chip(chip, args->args[0], NULL);
> + if (IS_ERR(dev))
> + return dev;
> +
> + /* The period cannot be changed on a per-PWM basis */
> + dev->args.period = pwm->real_period;
> + dev->args.polarity = PWM_POLARITY_NORMAL;
> + if (args->args[1] & PWM_POLARITY_INVERSED)
> + dev->args.polarity = PWM_POLARITY_INVERSED;
> +
> + return dev;
> +}
> +
> +static void sifive_pwm_update_clock(struct sifive_pwm_device *pwm,
> + unsigned long rate)
> +{
> + /* (1 << (16+scale)) * 10^9/rate = real_period */
> + unsigned long scale_pow = (pwm->approx_period * (u64)rate) / 1000000000;

NSEC_PER_SEC instead of 1000000000

> + int scale = clamp(ilog2(scale_pow) - 16, 0, 0xf);
> +
> + writel((1 << BIT_PWM_EN_ALWAYS) | (scale << BIT_PWM_SCALE),
> + pwm->regs + REG_PWMCFG);
> +
> + /* As scale <= 15 the shift operation cannot overflow. */
> + pwm->real_period = div64_ul(1000000000ULL << (16 + scale), rate);
> + dev_dbg(pwm->chip.dev, "New real_period = %u ns\n", pwm->real_period);
> +}
> +
> +static int sifive_pwm_clock_notifier(struct notifier_block *nb,
> + unsigned long event, void *data)
> +{
> + struct clk_notifier_data *ndata = data;
> + struct sifive_pwm_device *pwm =
> + container_of(nb, struct sifive_pwm_device, notifier);
> +
> + if (event == POST_RATE_CHANGE)
> + sifive_pwm_update_clock(pwm, ndata->new_rate);

Does this need locking? (Maybe not with the current state.)

> +
> + return NOTIFY_OK;
> +}
> +
> +static int sifive_pwm_probe(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + struct device_node *node = pdev->dev.of_node;
> + struct sifive_pwm_device *pwm;
> + struct pwm_chip *chip;
> + struct resource *res;
> + int ret;
> +
> + pwm = devm_kzalloc(dev, sizeof(*pwm), GFP_KERNEL);
> + if (!pwm)
> + return -ENOMEM;
> +
> + chip = &pwm->chip;
> + chip->dev = dev;
> + chip->ops = &sifive_pwm_ops;
> + chip->of_xlate = sifive_pwm_xlate;
> + chip->of_pwm_n_cells = 2;
> + chip->base = -1;
> + chip->npwm = 4;
> +
> + ret = of_property_read_u32(node, "sifive,approx-period-ns",
> + &pwm->approx_period);
> + if (ret < 0) {
> + dev_err(dev, "Unable to read sifive,approx-period from DTS\n");
> + return ret;
> + }
> +
> + res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> + pwm->regs = devm_ioremap_resource(dev, res);
> + if (IS_ERR(pwm->regs)) {
> + dev_err(dev, "Unable to map IO resources\n");
> + return PTR_ERR(pwm->regs);
> + }
> +
> + pwm->clk = devm_clk_get(dev, NULL);
> + if (IS_ERR(pwm->clk)) {
> + if (PTR_ERR(pwm->clk) != -EPROBE_DEFER)
> + dev_err(dev, "Unable to find controller clock\n");
> + return PTR_ERR(pwm->clk);
> + }
> +
> + ret = clk_prepare_enable(pwm->clk);
> + if (ret) {
> + dev_err(dev, "failed to enable clock for pwm: %d\n", ret);
> + return ret;
> + }
> +
> + /* Watch for changes to underlying clock frequency */
> + pwm->notifier.notifier_call = sifive_pwm_clock_notifier;
> + ret = clk_notifier_register(pwm->clk, &pwm->notifier);
> + if (ret) {
> + dev_err(dev, "failed to register clock notifier: %d\n", ret);
> + clk_disable_unprepare(pwm->clk);
> + return ret;
> + }
> +
> + /* Initialize PWM config */
> + sifive_pwm_update_clock(pwm, clk_get_rate(pwm->clk));
> +
> + ret = pwmchip_add(chip);
> + if (ret < 0) {
> + dev_err(dev, "cannot register PWM: %d\n", ret);
> + clk_notifier_unregister(pwm->clk, &pwm->notifier);
> + clk_disable_unprepare(pwm->clk);
> + return ret;
> + }

Can you please use a common error path using goto?

> + platform_set_drvdata(pdev, pwm);
> + dev_dbg(dev, "SiFive PWM chip registered %d PWMs\n", chip->npwm);
> +
> + return 0;
> +}
> +
> +static int sifive_pwm_remove(struct platform_device *dev)
> +{
> + struct sifive_pwm_device *pwm = platform_get_drvdata(dev);
> + int ret;
> +
> + ret = pwmchip_remove(&pwm->chip);
> + clk_notifier_unregister(pwm->clk, &pwm->notifier);
> + clk_disable_unprepare(pwm->clk);
> + return ret;
> +}
> +
> +static const struct of_device_id sifive_pwm_of_match[] = {
> + { .compatible = "sifive,pwm0" },
> + { .compatible = "sifive,fu540-c000-pwm" },

Do you really need both compatible strings here?

> + {},
> +};
> +MODULE_DEVICE_TABLE(of, sifive_pwm_of_match);
> +
> +static struct platform_driver sifive_pwm_driver = {
> + .probe = sifive_pwm_probe,
> + .remove = sifive_pwm_remove,
> + .driver = {
> + .name = "pwm-sifive",
> + .of_match_table = sifive_pwm_of_match,
> + },
> +};
> +module_platform_driver(sifive_pwm_driver);
> +
> +MODULE_DESCRIPTION("SiFive PWM driver");
> +MODULE_LICENSE("GPL v2");

Best regards
Uwe

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