[PATCH v2 4/4] pwm: add ChromeOS EC PWM driver

Brian Norris
2016-06-03T01:22:03Z

Use the new ChromeOS EC EC_CMD_PWM_{GET,SET}_DUTY commands to control
one or more PWMs attached to the Embedded Controller. Because the EC
allows us to modify the duty cycle (as a percentage, where U16_MAX is
100%) but not the period, we assign the period a fixed value of
EC_PWM_MAX_DUTY and reject all attempts to change it.

This driver supports only device tree at the moment, because that
provides a very flexible way of describing the relationship between PWMs
and their consumer devices (e.g., backlight). On a non-DT system, we'll
probably want to use the non-GENERIC addressing (i.e., we'll need to
make special device instances that will use EC_PWM_TYPE_KB_LIGHT or
EC_PWM_TYPE_DISPLAY_LIGHT), as well as the relatively inflexible
pwm_lookup infrastructure for matching devices. Defer that work for now.

Signed-off-by: Brian Norris <briannorris@chromium.org>
---
v2:
* refactor some abstractions to separate the PWM layer handling from
the cros_ec handling
* remove dynamic kzalloc()'s and rely on on-stack memory instead
* auto-probe the number of PWMs supported

drivers/pwm/Kconfig | 7 ++
drivers/pwm/Makefile | 1 +
drivers/pwm/pwm-cros-ec.c | 237 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 245 insertions(+)
create mode 100644 drivers/pwm/pwm-cros-ec.c

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index c182efc62c7b..4f2b16a50f42 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -137,6 +137,13 @@ config PWM_CRC
Generic PWM framework driver for Crystalcove (CRC) PMIC based PWM
control.

+config PWM_CROS_EC
+ tristate "ChromeOS EC PWM driver"
+ depends on MFD_CROS_EC
+ help
+ PWM driver for exposing a PWM attached to the ChromeOS Embedded
+ Controller.
+
config PWM_EP93XX
tristate "Cirrus Logic EP93xx PWM support"
depends on ARCH_EP93XX
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index dd35bc121a18..ffde923cf3df 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -11,6 +11,7 @@ obj-$(CONFIG_PWM_BFIN) += pwm-bfin.o
obj-$(CONFIG_PWM_BRCMSTB) += pwm-brcmstb.o
obj-$(CONFIG_PWM_CLPS711X) += pwm-clps711x.o
obj-$(CONFIG_PWM_CRC) += pwm-crc.o
+obj-$(CONFIG_PWM_CROS_EC) += pwm-cros-ec.o
obj-$(CONFIG_PWM_EP93XX) += pwm-ep93xx.o
obj-$(CONFIG_PWM_FSL_FTM) += pwm-fsl-ftm.o
obj-$(CONFIG_PWM_IMG) += pwm-img.o
diff --git a/drivers/pwm/pwm-cros-ec.c b/drivers/pwm/pwm-cros-ec.c
new file mode 100644
index 000000000000..de7f554a86e2
--- /dev/null
+++ b/drivers/pwm/pwm-cros-ec.c
@@ -0,0 +1,237 @@
+/*
+ * Copyright (C) 2016 Google, Inc
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2, as published by
+ * the Free Software Foundation.
+ *
+ * Expose a PWM controlled by the ChromeOS EC to the host processor.
+ */
+
+#include <linux/module.h>
+#include <linux/mfd/cros_ec.h>
+#include <linux/mfd/cros_ec_commands.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/slab.h>
+
+/**
+ * struct cros_ec_pwm_device - Driver data for EC PWM
+ *
+ * @dev: Device node
+ * @ec: Pointer to EC device
+ * @chip: PWM controller chip
+ */
+struct cros_ec_pwm_device {
+ struct device *dev;
+ struct cros_ec_device *ec;
+ struct pwm_chip chip;
+};
+
+static inline struct cros_ec_pwm_device *pwm_to_cros_ec_pwm(struct pwm_chip *c)
+{
+ return container_of(c, struct cros_ec_pwm_device, chip);
+}
+
+static int cros_ec_pwm_set_duty(struct cros_ec_device *ec, u8 index, u16 duty)
+{
+ struct {
+ struct cros_ec_command msg;
+ struct ec_params_pwm_set_duty params;
+ } buf;
+ struct ec_params_pwm_set_duty *params = &buf.params;
+ struct cros_ec_command *msg = &buf.msg;
+
+ memset(&buf, 0, sizeof(buf));
+
+ msg->version = 0;
+ msg->command = EC_CMD_PWM_SET_DUTY;
+ msg->insize = 0;
+ msg->outsize = sizeof(*params);
+
+ params->duty = duty;
+ params->pwm_type = EC_PWM_TYPE_GENERIC;
+ params->index = index;
+
+ return cros_ec_cmd_xfer_status(ec, msg);
+}
+
+static int cros_ec_pwm_get_duty(struct cros_ec_device *ec, u8 index)
+{
+ struct {
+ struct cros_ec_command msg;
+ union {
+ struct ec_params_pwm_get_duty params;
+ struct ec_response_pwm_get_duty resp;
+ };
+ } buf;
+ struct ec_params_pwm_get_duty *params = &buf.params;
+ struct ec_response_pwm_get_duty *resp = &buf.resp;
+ struct cros_ec_command *msg = &buf.msg;
+ int ret;
+
+ memset(&buf, 0, sizeof(buf));
+
+ msg->version = 0;
+ msg->command = EC_CMD_PWM_GET_DUTY;
+ msg->insize = sizeof(*params);
+ msg->outsize = sizeof(*resp);
+
+ params->pwm_type = EC_PWM_TYPE_GENERIC;
+ params->index = index;
+
+ ret = cros_ec_cmd_xfer_status(ec, msg);
+ if (ret < 0)
+ return ret;
+
+ return resp->duty;
+}
+
+static int cros_ec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
+ struct pwm_state *state)
+{
+ struct cros_ec_pwm_device *ec_pwm = pwm_to_cros_ec_pwm(chip);
+
+ /* The EC won't let us change the period */
+ if (state->period != EC_PWM_MAX_DUTY)
+ return -EINVAL;
+
+ return cros_ec_pwm_set_duty(ec_pwm->ec, pwm->hwpwm, state->duty_cycle);
+}
+
+static void cros_ec_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
+ struct pwm_state *state)
+{
+ struct cros_ec_pwm_device *ec_pwm = pwm_to_cros_ec_pwm(chip);
+ int ret;
+
+ ret = cros_ec_pwm_get_duty(ec_pwm->ec, pwm->hwpwm);
+ if (ret < 0) {
+ dev_err(chip->dev, "error getting initial duty: %d\n", ret);
+ return;
+ }
+
+ state->enabled = (ret > 0);
+ state->period = EC_PWM_MAX_DUTY;
+ state->duty_cycle = ret;
+}
+
+static struct pwm_device *
+cros_ec_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;
+
+ /* The EC won't let us change the period */
+ pwm->args.period = EC_PWM_MAX_DUTY;
+
+ return pwm;
+}
+
+static const struct pwm_ops cros_ec_pwm_ops = {
+ .get_state = cros_ec_pwm_get_state,
+ .apply = cros_ec_pwm_apply,
+ .owner = THIS_MODULE,
+};
+
+static int cros_ec_num_pwms(struct cros_ec_device *ec)
+{
+ int i, ret;
+
+ /* The index field is only 8 bits */
+ for (i = 0; i <= U8_MAX; i++) {
+ ret = cros_ec_pwm_get_duty(ec, i);
+ /*
+ * We look for SUCCESS, INVALID_COMMAND, or INVALID_PARAM responses;
+ * everything else is treated as an error
+ */
+ if (ret == -EECRESULT - EC_RES_INVALID_COMMAND)
+ return -ENODEV;
+ else if (ret == -EECRESULT - EC_RES_INVALID_PARAM)
+ return i;
+ else if (ret < 0)
+ return ret;
+ }
+
+ return U8_MAX;
+}
+
+static int cros_ec_pwm_probe(struct platform_device *pdev)
+{
+ struct cros_ec_device *ec = dev_get_drvdata(pdev->dev.parent);
+ struct device *dev = &pdev->dev;
+ struct cros_ec_pwm_device *ec_pwm;
+ struct pwm_chip *chip;
+ int ret;
+
+ if (!ec) {
+ dev_err(dev, "no parent EC device\n");
+ return -EINVAL;
+ }
+
+ ec_pwm = devm_kzalloc(dev, sizeof(*ec_pwm), GFP_KERNEL);
+ if (!ec_pwm)
+ return -ENOMEM;
+ chip = &ec_pwm->chip;
+ ec_pwm->ec = ec;
+
+ /* PWM chip */
+ chip->dev = dev;
+ chip->ops = &cros_ec_pwm_ops;
+ chip->of_xlate = cros_ec_pwm_xlate;
+ chip->of_pwm_n_cells = 1;
+ chip->base = -1;
+ ret = cros_ec_num_pwms(ec);
+ if (ret < 0) {
+ dev_err(dev, "Couldn't find PWMs: %d\n", ret);
+ return ret;
+ }
+ chip->npwm = ret;
+ dev_dbg(dev, "Probed %u PWMs\n", chip->npwm);
+
+ ret = pwmchip_add(chip);
+ if (ret < 0) {
+ dev_err(dev, "cannot register PWM: %d\n", ret);
+ return ret;
+ }
+
+ platform_set_drvdata(pdev, ec_pwm);
+
+ return ret;
+}
+
+static int cros_ec_pwm_remove(struct platform_device *dev)
+{
+ struct cros_ec_pwm_device *ec_pwm = platform_get_drvdata(dev);
+ struct pwm_chip *chip = &ec_pwm->chip;
+
+ return pwmchip_remove(chip);
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id cros_ec_pwm_of_match[] = {
+ { .compatible = "google,cros-ec-pwm" },
+ {},
+};
+MODULE_DEVICE_TABLE(of, cros_ec_pwm_of_match);
+#endif
+
+static struct platform_driver cros_ec_pwm_driver = {
+ .probe = cros_ec_pwm_probe,
+ .remove = cros_ec_pwm_remove,
+ .driver = {
+ .name = "cros-ec-pwm",
+ .of_match_table = of_match_ptr(cros_ec_pwm_of_match),
+ },
+};
+module_platform_driver(cros_ec_pwm_driver);
+
+MODULE_ALIAS("platform:cros-ec-pwm");
+MODULE_DESCRIPTION("ChromeOS EC PWM driver");
+MODULE_LICENSE("GPL v2");
--
2.8.0.rc3.226.g39d4020