pwm: Add a driver for Chrome OS EC PWM

This PWM is used in rk3399-gru-bob and rk3399-gru-kevin to control
the display brightness. We can only change the duty cycle, so on
set_config() we just try to match the duty cycle that dividing duty_ns
by period_ns gives us. To disable, we set the duty cycle to zero while
keeping the old value for when we want to re-enable it.

The cros_ec_set_pwm_duty() function is taken from Depthcharge's
cros_ec_set_bl_pwm_duty() but modified to use the generic pwm type.
The driver itself is very loosely based on rk_pwm.c for the general pwm
driver structure.

The devicetree binding file is from Linux, before it was converted to
YAML at 5df5a577a6b4 ("dt-bindings: pwm: Convert google,cros-ec-pwm.txt
to YAML format") in their repo.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

3 files changed, 94 insertions, 0 deletions

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index ccf81ab..cf7f4c6 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -9,6 +9,15 @@ config DM_PWM
 	  frequency/period can be controlled along with the proportion of that
 	  time that the signal is high.
 
+config PWM_CROS_EC
+	bool "Enable support for the Chrome OS EC PWM"
+	depends on DM_PWM
+	help
+	  This PWM is found on several Chrome OS devices and controlled by
+	  the Chrome OS embedded controller. It may be used to control the
+	  screen brightness and/or the keyboard backlight depending on the
+	  device.
+
 config PWM_EXYNOS
 	bool "Enable support for the Exynos PWM"
 	depends on DM_PWM
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 0b9d269..10d244b 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -10,6 +10,7 @@
 
 obj-$(CONFIG_DM_PWM)		+= pwm-uclass.o
 
+obj-$(CONFIG_PWM_CROS_EC)	+= cros_ec_pwm.o
 obj-$(CONFIG_PWM_EXYNOS)	+= exynos_pwm.o
 obj-$(CONFIG_PWM_IMX)		+= pwm-imx.o pwm-imx-util.o
 obj-$(CONFIG_PWM_MESON)		+= pwm-meson.o
diff --git a/drivers/pwm/cros_ec_pwm.c b/drivers/pwm/cros_ec_pwm.c
new file mode 100644
index 0000000..44f4105
--- /dev/null
+++ b/drivers/pwm/cros_ec_pwm.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <common.h>
+#include <cros_ec.h>
+#include <dm.h>
+#include <errno.h>
+#include <log.h>
+#include <pwm.h>
+
+struct cros_ec_pwm_priv {
+	bool enabled;
+	uint duty;
+};
+
+static int cros_ec_pwm_set_config(struct udevice *dev, uint channel,
+				  uint period_ns, uint duty_ns)
+{
+	struct cros_ec_pwm_priv *priv = dev_get_priv(dev);
+	uint duty;
+	int ret;
+
+	debug("%s: period_ns=%u, duty_ns=%u asked\n", __func__,
+	      period_ns, duty_ns);
+
+	/* No way to set the period, only a relative duty cycle */
+	duty = EC_PWM_MAX_DUTY * duty_ns / period_ns;
+	if (duty > EC_PWM_MAX_DUTY)
+		duty = EC_PWM_MAX_DUTY;
+
+	if (!priv->enabled) {
+		priv->duty = duty;
+		debug("%s: duty=%#x to-be-set\n", __func__, duty);
+		return 0;
+	}
+
+	ret = cros_ec_set_pwm_duty(dev->parent, channel, duty);
+	if (ret) {
+		debug("%s: duty=%#x failed\n", __func__, duty);
+		return ret;
+	}
+
+	priv->duty = duty;
+	debug("%s: duty=%#x set\n", __func__, duty);
+
+	return 0;
+}
+
+static int cros_ec_pwm_set_enable(struct udevice *dev, uint channel,
+				  bool enable)
+{
+	struct cros_ec_pwm_priv *priv = dev_get_priv(dev);
+	int ret;
+
+	ret = cros_ec_set_pwm_duty(dev->parent, channel,
+				   enable ? priv->duty : 0);
+	if (ret) {
+		debug("%s: enable=%d failed\n", __func__, enable);
+		return ret;
+	}
+
+	priv->enabled = enable;
+	debug("%s: enable=%d (duty=%#x) set\n", __func__,
+	      enable, priv->duty);
+
+	return 0;
+}
+
+static const struct pwm_ops cros_ec_pwm_ops = {
+	.set_config	= cros_ec_pwm_set_config,
+	.set_enable	= cros_ec_pwm_set_enable,
+};
+
+static const struct udevice_id cros_ec_pwm_ids[] = {
+	{ .compatible = "google,cros-ec-pwm" },
+	{ }
+};
+
+U_BOOT_DRIVER(cros_ec_pwm) = {
+	.name	= "cros_ec_pwm",
+	.id	= UCLASS_PWM,
+	.of_match = cros_ec_pwm_ids,
+	.ops	= &cros_ec_pwm_ops,
+	.priv_auto_alloc_size	= sizeof(struct cros_ec_pwm_priv),
+};