Re: [PATCH 3/3] pwm: Add Raspberry Pi Firmware based PWM bus

[Uwe Kleine-König]

Hello,

On Fri, Oct 09, 2020 at 05:30:30PM +0200, Nicolas Saenz Julienne wrote:
> Adds support to control the PWM bus available in official Raspberry Pi
> PoE HAT. Only RPi's co-processor has access to it, so commands have to
> be sent through RPi's firmware mailbox interface.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> ---
>  drivers/pwm/Kconfig           |   7 ++
>  drivers/pwm/Makefile          |   1 +
>  drivers/pwm/pwm-raspberrypi.c | 216 ++++++++++++++++++++++++++++++++++
>  3 files changed, 224 insertions(+)
>  create mode 100644 drivers/pwm/pwm-raspberrypi.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 63be5362fd3a..a76997ca37d0 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -379,6 +379,13 @@ config PWM_PXA
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-pxa.
>  
> +config PWM_RASPBERRYPI
> +	tristate "Raspberry Pi Firwmware PWM support"

s/Firwmware/Firmware/

> +	depends on RASPBERRYPI_FIRMWARE || (COMPILE_TEST && !RASPBERRYPI_FIRMWARE)

This is more complicated than necessary.

	depends on RASPBERRYPI_FIRMWARE || COMPILE_TEST

is logically equivalent.

> +	help
> +	  Enable Raspberry Pi firmware controller PWM bus used to control the
> +	  official RPI PoE hat
> +
>  config PWM_RCAR
>  	tristate "Renesas R-Car PWM support"
>  	depends on ARCH_RENESAS || COMPILE_TEST
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index cbdcd55d69ee..b557b549d9f3 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -35,6 +35,7 @@ obj-$(CONFIG_PWM_MXS)		+= pwm-mxs.o
>  obj-$(CONFIG_PWM_OMAP_DMTIMER)	+= pwm-omap-dmtimer.o
>  obj-$(CONFIG_PWM_PCA9685)	+= pwm-pca9685.o
>  obj-$(CONFIG_PWM_PXA)		+= pwm-pxa.o
> +obj-$(CONFIG_PWM_RASPBERRYPI)	+= pwm-raspberrypi.o
>  obj-$(CONFIG_PWM_RCAR)		+= pwm-rcar.o
>  obj-$(CONFIG_PWM_RENESAS_TPU)	+= pwm-renesas-tpu.o
>  obj-$(CONFIG_PWM_ROCKCHIP)	+= pwm-rockchip.o
> diff --git a/drivers/pwm/pwm-raspberrypi.c b/drivers/pwm/pwm-raspberrypi.c
> new file mode 100644
> index 000000000000..1ccff6b1ae34
> --- /dev/null
> +++ b/drivers/pwm/pwm-raspberrypi.c
> @@ -0,0 +1,216 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright 2020 Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> + */

Please add a paragraph here about the hardware. See pwm-sifive.c for a
template. (Please stick to the format there to simplify grepping.)

The things to point out there are:

 - No disable bit, so a disabled PWM is simulated by duty_cycle 0
 - Only normal polarity
 - Fixed period

Also add a note about if the currently running period is completed when
the hardware is reconfigured.

If possible please also add a link to a product page and/or
documentation.

> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +
> +#include <soc/bcm2835/raspberrypi-firmware.h>
> +#include <dt-bindings/pwm/raspberrypi,firmware-pwm.h>
> +
> +#define RPI_PWM_MAX_DUTY		255
> +#define RPI_PWM_PERIOD_NS		80000 /* 12.5KHz */

12.5 kHz

> +#define RPI_PWM_CUR_DUTY_REG		0x0
> +#define RPI_PWM_DEF_DUTY_REG		0x1
> +
> +struct raspberrypi_pwm {
> +	struct rpi_firmware *firmware;
> +	struct pwm_chip chip;
> +	unsigned int duty_cycle;
> +};
> +
> +struct raspberrypi_pwm_prop {
> +	__le32 reg;
> +	__le32 val;
> +	__le32 ret;
> +} __packed;
> +
> +static inline struct raspberrypi_pwm *to_raspberrypi_pwm(struct pwm_chip *chip)
> +{
> +	return container_of(chip, struct raspberrypi_pwm, chip);
> +}
> +
> +static int raspberrypi_pwm_set_property(struct rpi_firmware *firmware,
> +					u32 reg, u32 val)
> +{
> +	struct raspberrypi_pwm_prop msg = {
> +		.reg = cpu_to_le32(reg),
> +		.val = cpu_to_le32(val),
> +	};
> +	int ret;
> +
> +	ret = rpi_firmware_property(firmware, RPI_FIRMWARE_SET_POE_HAT_VAL,
> +				    &msg, sizeof(msg));
> +	if (ret)
> +		return ret;
> +	else if (msg.ret)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
> +static int raspberrypi_pwm_get_property(struct rpi_firmware *firmware,
> +					u32 reg, u32 *val)
> +{
> +	struct raspberrypi_pwm_prop msg = {
> +		.reg = reg
> +	};
> +	int ret;
> +
> +	ret = rpi_firmware_property(firmware, RPI_FIRMWARE_GET_POE_HAT_VAL,
> +				    &msg, sizeof(msg));
> +	if (ret)
> +		return ret;
> +	else if (msg.ret)
> +		return -EIO;
> +
> +	*val = le32_to_cpu(msg.val);
> +
> +	return 0;
> +}
> +
> +static void raspberrypi_pwm_get_state(struct pwm_chip *chip,
> +				      struct pwm_device *pwm,
> +				      struct pwm_state *state)
> +{
> +	struct raspberrypi_pwm *pc = to_raspberrypi_pwm(chip);
> +
> +	state->period = RPI_PWM_PERIOD_NS;
> +	state->duty_cycle = pc->duty_cycle * RPI_PWM_PERIOD_NS / RPI_PWM_MAX_DUTY;

Please round up the result of the division. (The idea is that if you
apply the state .get_state() returns this should yield no change.)

> +	state->enabled = !!(pc->duty_cycle);
> +	state->polarity = PWM_POLARITY_NORMAL;
> +}
> +
> +static int raspberrypi_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			         const struct pwm_state *state)
> +{
> +	struct raspberrypi_pwm *pc = to_raspberrypi_pwm(chip);
> +	unsigned int duty_cycle;
> +	int ret;
> +

You need to check for polarity here.

> +	if (!state->enabled)
> +		duty_cycle = 0;
> +	else
> +		duty_cycle = state->duty_cycle * RPI_PWM_MAX_DUTY /
> +			     RPI_PWM_PERIOD_NS;
> +
> +	if (duty_cycle == pc->duty_cycle)
> +		return 0;
> +
> +	pc->duty_cycle = duty_cycle;
> +	ret = raspberrypi_pwm_set_property(pc->firmware, RPI_PWM_CUR_DUTY_REG,
> +					   pc->duty_cycle);
> +	if (ret) {
> +		dev_err(chip->dev, "Failed to set duty cycle: %d\n", ret);
> +		return ret;
> +	}

What happens if duty_cycle happens to be bigger than RPI_PWM_MAX_DUTY?

I think the right thing to do here is:

	if (state->period < RPI_PWM_PERIOD_NS ||
	    state->polarity != PWM_POLARITY_NORMAL)
		return -EINVAL;

	if (!state->enabled)
		duty_cycle = 0
	else if (state->duty_cycle < RPI_PWM_PERIOD_NS)
		duty_cycle = state->duty_cycle * RPI_PWM_MAX_DUTY / RPI_PWM_PERIOD_NS;
	else
		duty_cycle = RPI_PWM_MAX_DUTY;

	ret = raspberrypi_pwm_set_property(pc->firmware, RPI_PWM_CUR_DUTY_REG,
					   pc->duty_cycle);
	if (ret)
		...

	pc->duty_cycle = duty_cycle;

> +
> +	ret = raspberrypi_pwm_set_property(pc->firmware, RPI_PWM_CUR_DUTY_REG,
> +					   pc->duty_cycle);
> +	if (ret) {
> +		dev_err(chip->dev, "Failed to set default duty cycle: %d\n", ret);
> +		return ret;
> +	}

Huh, why do you have to do this twice, just with different error
messages? I assume you want to set RPI_PWM_DEF_DUTY_REG? What is the
effect of writing this property?

> +
> +	return 0;
> +}
> +
> +static const struct pwm_ops raspberrypi_pwm_ops = {
> +	.get_state = raspberrypi_pwm_get_state,
> +	.apply = raspberrypi_pwm_apply,
> +	.owner = THIS_MODULE,
> +};
> +
> +static struct pwm_device *raspberrypi_pwm_xlate(struct pwm_chip *pc,
> +					const struct of_phandle_args *args)
> +{
> +	struct pwm_device *pwm;
> +
> +	if (args->args[0] >= pc->npwm)
> +		return ERR_PTR(-EINVAL);
> +
> +	pwm = pwm_request_from_chip(pc, args->args[0], NULL);
> +	if (IS_ERR(pwm))
> +		return pwm;
> +
> +	/* Firmwre won't let us change the period */

Firmware.

> +	pwm->args.period = RPI_PWM_PERIOD_NS;
> +
> +	return pwm;
> +}

I think you don't need this function. Just fix up period in .apply().

> +static int raspberrypi_pwm_probe(struct platform_device *pdev)
> +{
> +	struct device_node *firmware_node;
> +	struct device *dev = &pdev->dev;
> +	struct rpi_firmware *firmware;
> +	struct raspberrypi_pwm *pc;

What does "pc" stand for? I'd have used "rpipwm" or something similar.

> +	int ret;
> +
> +	firmware_node = of_get_parent(dev->of_node);
> +	if (!firmware_node) {
> +		dev_err(dev, "Missing firmware node\n");
> +		return -ENOENT;
> +	}
> +
> +	firmware = rpi_firmware_get(firmware_node);
> +	of_node_put(firmware_node);
> +	if (!firmware)
> +		return -EPROBE_DEFER;

I don't see a mechanism that prevents the driver providing the firmware
going away while the PWM is still in use.

> +	pc = devm_kzalloc(&pdev->dev, sizeof(*pc), GFP_KERNEL);
> +	if (!pc)
> +		return -ENOMEM;
> [...]
> +
> +static struct platform_driver raspberrypi_pwm_driver = {
> +	.driver = {
> +		.name = "raspberrypi-pwm",
> +		.of_match_table = raspberrypi_pwm_of_match,
> +	},
> +	.probe = raspberrypi_pwm_probe,
> +	.remove = raspberrypi_pwm_remove,
> +};
> +module_platform_driver(raspberrypi_pwm_driver);
> +
> +MODULE_AUTHOR("Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>");
> +MODULE_DESCRIPTION("Raspberry Pi Firwmare Based PWM Bus Driver");
> +MODULE_LICENSE("GPL v2");
> +

Please drop the empty line at the end of file.

Best regards
Uwe

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

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