Re: [PATCH v6 2/2] pwm: sifive: Add a driver for SiFive SoC PWM

From: Uwe Kleine-König
Date: Wed Feb 13 2019 - 05:35:10 EST

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In reply to: Yash Shah: "[PATCH v6 2/2] pwm: sifive: Add a driver for SiFive SoC PWM"
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Hello,

On Wed, Feb 13, 2019 at 02:56:18PM +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@xxxxxxxxxx>
> [Atish: Various fixes and code cleanup]
> Signed-off-by: Atish Patra <atish.patra@xxxxxxx>
> Signed-off-by: Yash Shah <yash.shah@xxxxxxxxxx>
> ---
> drivers/pwm/Kconfig | 11 ++
> drivers/pwm/Makefile | 1 +
> drivers/pwm/pwm-sifive.c | 311 +++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 323 insertions(+)
> create mode 100644 drivers/pwm/pwm-sifive.c
>
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index a8f47df..4a61d1a 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -380,6 +380,17 @@ 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
> + depends on RISCV || COMPILE_TEST
> + 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..c0eb90e
> --- /dev/null
> +++ b/drivers/pwm/pwm-sifive.c
> @@ -0,0 +1,311 @@
> +// 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
> + */
> +#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 PWM_SIFIVE_PWMCFG 0x0
> +#define PWM_SIFIVE_PWMCOUNT 0x8
> +#define PWM_SIFIVE_PWMS 0x10
> +#define PWM_SIFIVE_PWMCMP0 0x20
> +
> +/* PWMCFG fields */
> +#define PWM_SIFIVE_PWMCFG_SCALE 0
> +#define PWM_SIFIVE_PWMCFG_STICKY 8
> +#define PWM_SIFIVE_PWMCFG_ZERO_CMP 9
> +#define PWM_SIFIVE_PWMCFG_DEGLITCH 10
> +#define PWM_SIFIVE_PWMCFG_EN_ALWAYS 12

PWM_SIFIVE_PWMCFG_EN_ALWAYS is always used as

BIT(PWM_SIFIVE_PWMCFG_EN_ALWAYS)

so defining this as BIT(12) directly makes some expressions below easier
to read.

> +#define PWM_SIFIVE_PWMCFG_EN_ONCE 13
> +#define PWM_SIFIVE_PWMCFG_CENTER 16
> +#define PWM_SIFIVE_PWMCFG_GANG 24
> +#define PWM_SIFIVE_PWMCFG_IP 28
> +
> +/* PWM_SIFIVE_SIZE_PWMCMP is used to calculate offset for pwmcmpX registers */
> +#define PWM_SIFIVE_SIZE_PWMCMP 4
> +#define PWM_SIFIVE_CMPWIDTH 16
> +
> +struct pwm_sifive_ddata {
> + struct pwm_chip chip;
> + struct notifier_block notifier;
> + struct clk *clk;
> + void __iomem *regs;
> + unsigned int real_period;
> + int user_count;
> +};
> +
> +static inline
> +struct pwm_sifive_ddata *pwm_sifive_chip_to_ddata(struct pwm_chip *c)
> +{
> + return container_of(c, struct pwm_sifive_ddata, chip);
> +}
> +
> +static int pwm_sifive_request(struct pwm_chip *chip, struct pwm_device *dev)
> +{
> + struct pwm_sifive_ddata *pwm = pwm_sifive_chip_to_ddata(chip);
> +
> + pwm->user_count++;
> +
> + return 0;
> +}
> +
> +static void pwm_sifive_free(struct pwm_chip *chip, struct pwm_device *dev)
> +{
> + struct pwm_sifive_ddata *pwm = pwm_sifive_chip_to_ddata(chip);
> +
> + pwm->user_count--;
> +}
> +
> +static void pwm_sifive_update_clock(struct pwm_sifive_ddata *pwm,
> + unsigned long rate)
> +{
> + /* (1 << (16+scale)) * 10^9/rate = real_period */

Maybe you want to mention here the relation between 16 and
PWM_SIFIVE_CMPWIDTH.

> + unsigned long scale_pow =
> + div64_ul(pwm->real_period * (u64)rate, NSEC_PER_SEC);
> + int scale = clamp(ilog2(scale_pow) - PWM_SIFIVE_CMPWIDTH, 0, 0xf);
> +
> + writel((1 << PWM_SIFIVE_PWMCFG_EN_ALWAYS) | (scale <<
> + PWM_SIFIVE_PWMCFG_SCALE), pwm->regs + PWM_SIFIVE_PWMCFG);

I think this would be better readable with the newline after the |. With
my editor's configuration when broken like this, the 2nd line would be
intended with the opening ( after the |.

> +
> + /* As scale <= 15 the shift operation cannot overflow. */
> + pwm->real_period = div64_ul(1000000000ULL << (PWM_SIFIVE_CMPWIDTH +
> + scale), rate);

ditto. Maybe break after the =?

> + dev_dbg(pwm->chip.dev, "New real_period = %u ns\n", pwm->real_period);
> +}
> +
> +static void pwm_sifive_get_state(struct pwm_chip *chip, struct pwm_device *dev,
> + struct pwm_state *state)
> +{
> + struct pwm_sifive_ddata *pwm = pwm_sifive_chip_to_ddata(chip);
> + u32 duty;
> + int val;
> +
> + duty = readl(pwm->regs + PWM_SIFIVE_PWMCMP0 + dev->hwpwm *
> + PWM_SIFIVE_SIZE_PWMCMP);
> +
> + val = readl(pwm->regs + PWM_SIFIVE_PWMCFG);
> + state->enabled = (val & BIT(PWM_SIFIVE_PWMCFG_EN_ALWAYS)) > 0;
> +
> + val &= 0x0F;
> + pwm->real_period = div64_ul(1000000000ULL << (PWM_SIFIVE_CMPWIDTH +
> + val), clk_get_rate(pwm->clk));

Another bad line break.

> +
> + state->period = pwm->real_period;
> + state->duty_cycle = ((u64)duty * pwm->real_period) >>
> + PWM_SIFIVE_CMPWIDTH;
> + state->polarity = PWM_POLARITY_INVERSED;
> +}
> +
> +static int pwm_sifive_enable(struct pwm_chip *chip, struct pwm_device *dev,
> + bool enable)
> +{
> + struct pwm_sifive_ddata *pwm = pwm_sifive_chip_to_ddata(chip);
> + u32 val;
> + int ret;
> +
> + if (enable) {
> + ret = clk_enable(pwm->clk);
> + if (ret) {
> + dev_err(pwm->chip.dev, "Enable clk failed:%d\n", ret);
> + return ret;
> + }
> + }
> +
> + val = readl(pwm->regs + PWM_SIFIVE_PWMCFG);
> +
> + if (enable)
> + val |= BIT(PWM_SIFIVE_PWMCFG_EN_ALWAYS);
> + else
> + val &= ~BIT(PWM_SIFIVE_PWMCFG_EN_ALWAYS);
> +
> + writel(val, pwm->regs + PWM_SIFIVE_PWMCFG);
> +
> + if (!enable)
> + clk_disable(pwm->clk);

A disabled PWM is supposed to output an inactive signal. If the PWM runs
at (near) 100% and you disable it, does it reliably give that inactive
signal after completing the currently running period?

> +
> + return 0;
> +}
> +
> +static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *dev,
> + struct pwm_state *state)
> +{
> + struct pwm_sifive_ddata *pwm = pwm_sifive_chip_to_ddata(chip);
> + unsigned int duty_cycle;
> + u32 frac, val;
> + struct pwm_state cur_state;
> + bool enabled;
> + int ret;
> +
> + pwm_get_state(dev, &cur_state);
> + enabled = cur_state.enabled;
> +
> + if (state->polarity != PWM_POLARITY_INVERSED)
> + return -EINVAL;
> +
> + if (state->period != cur_state.period) {
> + if (pwm->user_count != 1)
> + return -EINVAL;

I think we need locking here. Consider two pwm users on two CPUs:

CPU1 CPU2
pwm_sifive_apply(pwm0, period=A, ...)
check user_count==1 -> good
... pwm1 = pwm_get(...)
... pwm_sifive_apply(pwm1, period=B...)
... configure based on B
pwm_sifive_update_clock()

Also I wonder if we should change the period if the user requested
enabled=false.

> + pwm->real_period = state->period;
> + pwm_sifive_update_clock(pwm, clk_get_rate(pwm->clk));

If you change from

.period = A
.duty_cycle = B

to

.period = C
.duty_cycle = D

the output pin might see a period with

.period = C
.duty_cycle = B

right? I think this is not fixable, but this needs a prominent comment.

> + }
> +
> + if (!state->enabled && enabled) {
> + ret = pwm_sifive_enable(chip, dev, false);
> + if (ret)
> + return ret;
> + enabled = false;
> + }
> +
> + duty_cycle = state->duty_cycle;
> + frac = div_u64((u64)duty_cycle * (1 << PWM_SIFIVE_CMPWIDTH) +
> + (1 << PWM_SIFIVE_CMPWIDTH) / 2, state->period);
> + /* The hardware cannot generate a 100% duty cycle */

@Thierry: Do you consider this bad enough that pwm_apply_state should
fail if 100% is requested?

> + frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
> +
> + val = readl(pwm->regs + PWM_SIFIVE_PWMCFG);
> + val |= BIT(PWM_SIFIVE_PWMCFG_DEGLITCH);
> + writel(val, pwm->regs + PWM_SIFIVE_PWMCFG);
> +
> + writel(frac, pwm->regs + PWM_SIFIVE_PWMCMP0 + dev->hwpwm *
> + PWM_SIFIVE_SIZE_PWMCMP);
> +
> + val &= ~BIT(PWM_SIFIVE_PWMCFG_DEGLITCH);

Doesn't that come too early? I thought the right thing was to keep it
set all the time. With this code I think you might see a duty cycle of
50 when going from 60 to 40.

> + writel(val, pwm->regs + PWM_SIFIVE_PWMCFG);
> +
> + if (state->enabled != enabled) {
> + ret = pwm_sifive_enable(chip, dev, state->enabled);
> + if (ret)
> + return ret;
> + }

FTR: This doesn't block until the newly configured state is active.

> +
> + return 0;
> +}

Best regards
Uwe

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

Next message: Philipp Zabel: "Re: [PATCH v4 1/4] gpu: ipu-v3: ipu-ic: Rename yuv2rgb encoding matrices"
Previous message: Rafael J. Wysocki: "Re: [PATCH v4] cpufreq: intel_pstate: Reporting reasons why driver prematurely exit"
In reply to: Yash Shah: "[PATCH v6 2/2] pwm: sifive: Add a driver for SiFive SoC PWM"
Next in thread: Thierry Reding: "Re: [PATCH v6 2/2] pwm: sifive: Add a driver for SiFive SoC PWM"
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