[PATCH 3/3] pwm: Add Raspberry Pi Firmware based PWM bus
Uwe Kleine-König
u.kleine-koenig at pengutronix.de
Mon Oct 12 03:06:26 EDT 2020
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 at suse.de>
> ---
> 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 at suse.de>
> + */
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 at suse.de>");
> +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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