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 <nsaenzjulie...@suse.de>
---

Changes since v2:
 - Use devm_rpi_firmware_get()
 - Rename driver
 - Small cleanups

Changes since v1:
 - Use default pwm bindings and get rid of xlate() function
 - Correct spelling errors
 - Correct apply() function
 - Round values
 - Fix divisions in arm32 mode
 - Small cleanups

 drivers/pwm/Kconfig               |   9 ++
 drivers/pwm/Makefile              |   1 +
 drivers/pwm/pwm-raspberrypi-poe.c | 216 ++++++++++++++++++++++++++++++
 3 files changed, 226 insertions(+)
 create mode 100644 drivers/pwm/pwm-raspberrypi-poe.c

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index b2a87fd7e8fb..3445984a5a50 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -409,6 +409,15 @@ config PWM_PXA
          To compile this driver as a module, choose M here: the module
          will be called pwm-pxa.
 
+config PWM_RASPBERRYPI_POE
+       tristate "Raspberry Pi Firwmware PoE Hat PWM support"
+       # Make sure not 'y' when RASPBERRYPI_FIRMWARE is 'm'. This can only
+       # happen when COMPILE_TEST=y, hence the added !RASPBERRYPI_FIRMWARE.
+       depends on RASPBERRYPI_FIRMWARE || (COMPILE_TEST && 
!RASPBERRYPI_FIRMWARE)
+       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 18b89d7fd092..ed28d7bd4c64 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -38,6 +38,7 @@ 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-$(CONFIG_PWM_RASPBERRYPI_POE)      += pwm-raspberrypi-poe.o
 obj-$(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-poe.c 
b/drivers/pwm/pwm-raspberrypi-poe.c
new file mode 100644
index 000000000000..91cd826a36f3
--- /dev/null
+++ b/drivers/pwm/pwm-raspberrypi-poe.c
@@ -0,0 +1,216 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2020 Nicolas Saenz Julienne <nsaenzjulie...@suse.de>
+ * For more information on Raspberry Pi's PoE hat see:
+ * https://www.raspberrypi.org/products/poe-hat/
+ *
+ * Limitations:
+ *  - No disable bit, so a disabled PWM is simulated by duty_cycle 0
+ *  - Only normal polarity
+ *  - Fixed 12.5 kHz period
+ *
+ * The current period is completed when HW is reconfigured.
+ */
+
+#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 /* 12.5 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;
+       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;
+       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 *rpipwm = to_raspberrypi_pwm(chip);
+
+       state->period = RPI_PWM_PERIOD_NS;
+       state->duty_cycle = DIV_ROUND_CLOSEST(rpipwm->duty_cycle * 
RPI_PWM_PERIOD_NS,
+                                             RPI_PWM_MAX_DUTY);
+       state->enabled = !!(rpipwm->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 *rpipwm = to_raspberrypi_pwm(chip);
+       unsigned int duty_cycle;
+       int ret;
+
+        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 = DIV_ROUND_CLOSEST_ULL(state->duty_cycle * 
RPI_PWM_MAX_DUTY,
+                                                  RPI_PWM_PERIOD_NS);
+        else
+                duty_cycle = RPI_PWM_MAX_DUTY;
+
+       if (duty_cycle == rpipwm->duty_cycle)
+               return 0;
+
+       ret = raspberrypi_pwm_set_property(rpipwm->firmware, 
RPI_PWM_CUR_DUTY_REG,
+                                          duty_cycle);
+       if (ret) {
+               dev_err(chip->dev, "Failed to set duty cycle: %d\n", ret);
+               return ret;
+       }
+
+       /*
+        * This sets the default duty cycle after resetting the board, we
+        * updated it every time to mimic Raspberry Pi's downstream's driver
+        * behaviour.
+        */
+       ret = raspberrypi_pwm_set_property(rpipwm->firmware, 
RPI_PWM_DEF_DUTY_REG,
+                                          duty_cycle);
+       if (ret) {
+               dev_err(chip->dev, "Failed to set default duty cycle: %d\n", 
ret);
+               return ret;
+       }
+
+        rpipwm->duty_cycle = duty_cycle;
+
+       return 0;
+}
+
+static const struct pwm_ops raspberrypi_pwm_ops = {
+       .get_state = raspberrypi_pwm_get_state,
+       .apply = raspberrypi_pwm_apply,
+       .owner = THIS_MODULE,
+};
+
+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 *rpipwm;
+       int ret;
+
+       firmware_node = of_get_parent(dev->of_node);
+       if (!firmware_node) {
+               dev_err(dev, "Missing firmware node\n");
+               return -ENOENT;
+       }
+
+       firmware = devm_rpi_firmware_get(&pdev->dev, firmware_node);
+       of_node_put(firmware_node);
+       if (!firmware)
+               return -EPROBE_DEFER;
+
+       rpipwm = devm_kzalloc(&pdev->dev, sizeof(*rpipwm), GFP_KERNEL);
+       if (!rpipwm)
+               return -ENOMEM;
+
+       rpipwm->firmware = firmware;
+       rpipwm->chip.dev = dev;
+       rpipwm->chip.ops = &raspberrypi_pwm_ops;
+       rpipwm->chip.base = -1;
+       rpipwm->chip.npwm = RASPBERRYPI_FIRMWARE_PWM_NUM;
+
+       platform_set_drvdata(pdev, rpipwm);
+
+       ret = raspberrypi_pwm_get_property(rpipwm->firmware, 
RPI_PWM_CUR_DUTY_REG,
+                                          &rpipwm->duty_cycle);
+       if (ret) {
+               dev_err(dev, "Failed to get duty cycle: %d\n", ret);
+               return ret;
+       }
+
+       return pwmchip_add(&rpipwm->chip);
+}
+
+static int raspberrypi_pwm_remove(struct platform_device *pdev)
+{
+       struct raspberrypi_pwm *rpipwm = platform_get_drvdata(pdev);
+
+       return pwmchip_remove(&rpipwm->chip);
+}
+
+static const struct of_device_id raspberrypi_pwm_of_match[] = {
+       { .compatible = "raspberrypi,firmware-pwm", },
+       { }
+};
+MODULE_DEVICE_TABLE(of, raspberrypi_pwm_of_match);
+
+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 <nsaenzjulie...@suse.de>");
+MODULE_DESCRIPTION("Raspberry Pi Firwmare Based PWM Bus Driver");
+MODULE_LICENSE("GPL v2");
-- 
2.29.2

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