greybus: platform: Add platform driver for DB3 AP bridge

With DB3, we now have AP as a master as far as AP bridges are concerned.
SVC will talk only to AP and AP will control bridges; unlike other
module interfaces.

So AP supposed to manage/control bridges in all power states including
power on reset.

During power on reset AP should follow below sequence -

Sequence (treated as a Cold Boot)

Stage-1
=======
AP:
 - Power On (Power up from PMIC to AP)
 - AP start booting
   Since power to AP bridges are controlled through gpio, power is gated
   to APB1 & 2
   No ref_clk to APB available (under SVC's control)
 - AP configures USB hub to enable HSIC interface to APB
 - As part of platform driver probe, AP follow below sequence
   - Set the pinctrl in default state
   - Hold APBs in reset by pulling down reset pin
   - Enable power to APB by enabling regulator and switches
   - De-assert (set 'low') 'boot_ret' signal
 - AP will assert (set 'high') the wake_detect signal, triggering
   connect/detect event to the SVC
 - AP waits for wake pulse from SVC

 SVC:
 - Power On (power up from PMIC to SVC)
 - SVC starts booting
 - SVC will de-assert reset signal to unipro switch
   - Switch starts booting
 - SVC confirms switch boot status using SPI (or something)
 - SVC waits for 300 msec (ES2 known issue)
 - SVC waits for detect/connect event from AP

Stage-2
=======
SVC:
 - ON connect/detect event, SVC send back wake pulse (cold boot)
   to AP over wake_detect pin, if SVC boot is completed.

AP:
 - On wake pulse from SVC (for cold boot), AP de-asserts (set high')
   reset signal to APB 1 and/or 2
 - Bridges starts booting
 - Eventually Unipro linkup occurs

Testing:

 - Build tested against Helium kernel
 - Due to unavailability of MSM and DB3 platform, only minimal testing
   has been done.
 - Code has been modified for validation on Helium + SDB platform.
    Mostly dts changes for gpio numbers
    And debug messages to check gpio values
 - On Helium + SDB platform, with addition of debug messages validated
   the sequence.

TODO list:

 - Currently _only_ supports power on sequence (cold boot).
   Both warm and cold boot support. Cold and Warm boot is
   differentiated based on pulse width of wake_detect signal
      >=5 msec = Cold boot else Warm boot
 - No support for Power management
   So the "power-down", "power-off", "wake_in" and "wake_out"
   signals are not explored/implemented.
 - Support for Work thread
    repetitive wake signal if no response from peer
    May required for PM support, as we have delays in the sequences
 - pinctrl states, specially to make sure we enable right pullup or pulldown
   when we set wake_detect pin to input
 - Convert gpio list into an array, and associated xxx-gpio-name property
Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/Makefile

@@ -34,6 +34,7 @@ gb-light-y := light.o
 gb-raw-y := raw.o
 gb-es1-y := es1.o
 gb-es2-y := es2.o
+gb-db3-y := db3-platform.o
 
 obj-m += greybus.o
 obj-m += gb-phy.o
@@ -44,6 +45,7 @@ obj-m += gb-light.o
 obj-m += gb-raw.o
 obj-m += gb-es1.o
 obj-m += gb-es2.o
+obj-m += gb-db3.o
 
 KERNELVER		?= $(shell uname -r)
 KERNELDIR 		?= /lib/modules/$(KERNELVER)/build

drivers/staging/greybus/db3-platform.c

+/*
+ * DB3 Platform driver for AP bridge control interface.
+ *
+ * Copyright 2014-2015 Google Inc.
+ * Copyright 2014-2015 Linaro Ltd.
+ *
+ * Released under the GPLv2 only.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/sched.h>
+#include <linux/pm.h>
+#include <linux/delay.h>
+#include <linux/platform_device.h>
+#include <linux/gpio.h>
+#include <linux/of_platform.h>
+#include <linux/of_gpio.h>
+#include <linux/of_irq.h>
+#include <linux/spinlock.h>
+#include <linux/regulator/consumer.h>
+#include <linux/pinctrl/consumer.h>
+
+enum apb_state {
+	APB_STATE_OFF,
+	APB_STATE_ACTIVE,
+	APB_STATE_STANDBY,
+};
+
+/*
+ * Control GPIO signals to and from AP <=> AP Bridges
+ */
+struct apb_ctrl_gpios {
+	int wake_detect; /* bi-dir, maps to WAKE_MOD and WAKE_FRAME signals */
+	int reset;
+	int boot_ret;
+	int pwroff;
+	int wake_in;
+	int wake_out;
+	int pwrdn;
+};
+
+struct apb_ctrl_drvdata {
+	struct apb_ctrl_gpios ctrl;
+
+	unsigned int wake_detect_irq;
+	enum apb_state state;
+
+	struct regulator *vcore;
+	struct regulator *vio;
+
+	struct pinctrl *pinctrl;
+	struct pinctrl_state *pin_default;
+
+	/* To protect concurrent access of GPIO registers, need protection */
+	spinlock_t lock;
+};
+
+static inline void assert_wake(unsigned int wake_detect)
+{
+	gpio_set_value(wake_detect, 1);
+}
+
+static inline void deassert_wake(unsigned int wake_detect)
+{
+	gpio_set_value(wake_detect, 0);
+}
+
+static irqreturn_t apb_ctrl_wake_detect_irq(int irq, void *devid)
+{
+	struct apb_ctrl_drvdata *apb_data = devid;
+	unsigned long flags;
+
+	/*
+	 * TODO:
+	 * Since currently SoC gpio's are being used we are safe here
+	 * But ideally we should create a workqueue and process the control
+	 * signals, especially when we start using GPIO's over slow
+	 * buses like I2C.
+	 */
+	if (!gpio_is_valid(apb_data->ctrl.wake_detect) &&
+			!gpio_is_valid(apb_data->ctrl.reset))
+		return IRQ_HANDLED; /* Should it be IRQ_NONE ?? */
+
+	spin_lock_irqsave(&apb_data->lock, flags);
+
+	if (apb_data->state != APB_STATE_ACTIVE) {
+		/* Bring bridge out of reset on this event */
+		gpio_set_value(apb_data->ctrl.reset, 0);
+		apb_data->state = APB_STATE_ACTIVE;
+	} else {
+		/*
+		 * Assert Wake_OUT signal to APB
+		 * It would resemble WakeDetect module's signal pass-through
+		 */
+		/*
+		 * We have to generate the pulse, so we may need to schedule
+		 * workqueue here.
+		 *
+		 * Also, since we are using both rising and falling edge for
+		 * interrupt trigger, we may not need workqueue. Just pass
+		 * through the value to bridge.
+		 * Just read GPIO value and pass it to the bridge
+		 */
+	}
+
+	spin_unlock_irqrestore(&apb_data->lock, flags);
+
+	return IRQ_HANDLED;
+}
+
+static void apb_ctrl_cleanup(struct apb_ctrl_drvdata *apb_data)
+{
+	if (apb_data->vcore && regulator_is_enabled(apb_data->vcore) > 0)
+		regulator_disable(apb_data->vcore);
+
+	if (apb_data->vio && regulator_is_enabled(apb_data->vio) > 0)
+		regulator_disable(apb_data->vio);
+
+	/* As part of exit, put APB back in reset state */
+	if (gpio_is_valid(apb_data->ctrl.reset))
+		gpio_set_value(apb_data->ctrl.reset, 1);
+
+	/* TODO: May have to send an event to SVC about this exit */
+}
+
+/*
+ * Note: Please do not modify the below sequence, as it is as per the spec
+ */
+static int apb_ctrl_init_seq(struct device *dev,
+		struct apb_ctrl_drvdata *apb_data)
+{
+	int ret;
+
+	pinctrl_select_state(apb_data->pinctrl, apb_data->pin_default);
+
+	/* Hold APB in reset state */
+	ret = devm_gpio_request_one(dev, apb_data->ctrl.reset,
+			GPIOF_OUT_INIT_LOW, "reset");
+	if (ret) {
+		dev_err(dev, "Failed requesting reset gpio %d\n",
+				apb_data->ctrl.reset);
+		return ret;
+	}
+
+	/* Enable power to APB */
+	if (apb_data->vcore) {
+		ret = regulator_enable(apb_data->vcore);
+		if (ret) {
+			dev_err(dev, "failed to enable core regulator\n");
+			return ret;
+		}
+	}
+
+	if (apb_data->vio) {
+		ret = regulator_enable(apb_data->vio);
+		if (ret) {
+			dev_err(dev, "failed to enable IO regulator\n");
+			return ret;
+		}
+	}
+
+	/*
+	 * We should be safe here to deassert boot retention signal, as
+	 * we are only supporting cold boot as of now.
+	 */
+	ret = devm_gpio_request_one(dev, apb_data->ctrl.boot_ret,
+			GPIOF_OUT_INIT_LOW, "boot retention");
+	if (ret) {
+		dev_err(dev, "Failed requesting reset gpio %d\n",
+				apb_data->ctrl.boot_ret);
+		return ret;
+	}
+
+	ret = devm_gpio_request(dev, apb_data->ctrl.wake_detect, "wake detect");
+	if (ret)
+		dev_err(dev, "Failed requesting wake_detect gpio %d\n",
+				apb_data->ctrl.wake_detect);
+
+	return ret;
+}
+
+static int apb_ctrl_get_devtree_data(struct device *dev,
+		struct apb_ctrl_drvdata *apb_data)
+{
+	struct device_node *np = dev->of_node;
+
+	/* fetch control signals */
+	apb_data->ctrl.wake_detect = of_get_named_gpio(np, "wake-detect-gpios", 0);
+	if (apb_data->ctrl.wake_detect < 0 ||
+			!gpio_is_valid(apb_data->ctrl.wake_detect)) {
+		dev_err(dev, "failed to get wake detect gpio\n");
+		return apb_data->ctrl.wake_detect;
+	}
+
+	apb_data->ctrl.reset = of_get_named_gpio(np, "reset-gpios", 0);
+	if (apb_data->ctrl.wake_detect < 0 ||
+			!gpio_is_valid(apb_data->ctrl.reset)) {
+		dev_err(dev, "failed to get wake detect gpio\n");
+		return apb_data->ctrl.wake_detect;
+	}
+
+	apb_data->ctrl.boot_ret = of_get_named_gpio(np, "boot-ret-gpios", 0);
+	if (apb_data->ctrl.boot_ret < 0 ||
+			!gpio_is_valid(apb_data->ctrl.boot_ret)) {
+		dev_err(dev, "failed to get boot retention gpio\n");
+		return apb_data->ctrl.boot_ret;
+	}
+
+	/* It's not mandetory to support power management interface */
+	apb_data->ctrl.pwroff = of_get_named_gpio(np, "pwr-off-gpios", 0);
+	if (apb_data->ctrl.pwroff < 0 ||
+			!gpio_is_valid(apb_data->ctrl.pwroff))
+		dev_info(dev, "failed to get power off gpio\n");
+
+	apb_data->ctrl.pwrdn = of_get_named_gpio(np, "pwr-down-gpios", 0);
+	if (apb_data->ctrl.pwrdn < 0 ||
+			!gpio_is_valid(apb_data->ctrl.pwrdn))
+		dev_info(dev, "failed to get power down gpio\n");
+
+	/* Regulators are optional, as we may have fixed supply coming in */
+	apb_data->vcore = devm_regulator_get(dev, "vcore");
+	if (IS_ERR_OR_NULL(apb_data->vcore)) {
+		dev_info(dev, "no core regulator found\n");
+		apb_data->vcore = NULL;
+	}
+
+	apb_data->vio = devm_regulator_get(dev, "vio");
+	if (IS_ERR_OR_NULL(apb_data->vio)) {
+		dev_info(dev, "no IO regulator found\n");
+		apb_data->vio = NULL;
+	}
+
+	apb_data->pinctrl = devm_pinctrl_get(dev);
+	if (IS_ERR(apb_data->pinctrl)) {
+		dev_err(dev, "could not get pinctrl handle\n");
+		return PTR_ERR(apb_data->pinctrl);
+	}
+	apb_data->pin_default = pinctrl_lookup_state(apb_data->pinctrl, "default");
+	if (IS_ERR(apb_data->pin_default)) {
+		dev_err(dev, "could not get default pin state\n");
+		return PTR_ERR(apb_data->pin_default);
+	}
+
+	return 0;
+}
+
+static int apb_ctrl_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct apb_ctrl_drvdata *apb_data;
+	int ret;
+
+	apb_data = devm_kzalloc(&pdev->dev, sizeof(*apb_data), GFP_KERNEL);
+	if (!apb_data)
+		return -ENOMEM;
+
+	ret = apb_ctrl_get_devtree_data(dev, apb_data);
+	if (ret) {
+		dev_err(dev, "failed to get devicetree data %d\n", ret);
+		return ret;
+	}
+
+	ret = apb_ctrl_init_seq(dev, apb_data);
+	if (ret) {
+		dev_err(dev, "failed to set init state of control signal %d\n",
+				ret);
+		goto exit;
+	}
+
+	platform_set_drvdata(pdev, apb_data);
+
+	apb_data->state = APB_STATE_OFF;
+	/*
+	 * Assert AP module detect signal by pulling wake_detect low
+	 */
+	deassert_wake(apb_data->ctrl.wake_detect);
+
+	/*
+	 * In order to receive an interrupt, the GPIO must be set to input mode
+	 *
+	 * As per WDM spec, for the cold boot, the wake pulse must be
+	 * >= 5000 usec, but at this stage it is power up sequence,
+	 * so we always treat it as cold boot.
+	 */
+	gpio_direction_input(apb_data->ctrl.wake_detect);
+
+	ret = devm_request_irq(dev, gpio_to_irq(apb_data->ctrl.wake_detect),
+			apb_ctrl_wake_detect_irq,
+			IRQF_TRIGGER_RISING,
+			"wake detect", apb_data);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to request wake detect IRQ\n");
+		goto exit;
+	}
+
+	/*
+	 * Interrupt handling for WAKE_IN (from bridge) signal is required
+	 *
+	 * Assumption here is, AP already would have woken up and in the
+	 * WAKE_IN/WAKE_FRAME event from bridge, as AP would pass-through event
+	 * to SVC.
+	 *
+	 * Not sure anything else needs to take care here.
+	 */
+	dev_err(dev, "Device registered successfully \n");
+	return 0;
+
+exit:
+	apb_ctrl_cleanup(apb_data);
+	return ret;
+}
+
+static int apb_ctrl_remove(struct platform_device *pdev)
+{
+	struct apb_ctrl_drvdata *apb_data = platform_get_drvdata(pdev);
+
+	if (apb_data)
+		apb_ctrl_cleanup(apb_data);
+
+	platform_set_drvdata(pdev, NULL);
+
+	return 0;
+}
+
+static int apb_ctrl_suspend(struct device *dev)
+{
+	/*
+	 * If timing profile premits, we may shutdown bridge
+	 * completely
+	 *
+	 * TODO: sequence ??
+	 *
+	 * Also, need to make sure we meet precondition for unipro suspend
+	 * Precondition: Definition ???
+	 */
+	return 0;
+}
+
+static int apb_ctrl_resume(struct device *dev)
+{
+	/*
+	 * Atleast for ES2 we have to meet the delay requirement between
+	 * unipro switch and AP bridge init, depending on whether bridge is in
+	 * OFF state or standby state.
+	 *
+	 * Based on whether bridge is in standby or OFF state we may have to
+	 * assert multiple signals. Please refer to WDM spec, for more info.
+	 *
+	 */
+	return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(apb_ctrl_pm_ops, apb_ctrl_suspend, apb_ctrl_resume);
+
+static struct of_device_id apb_ctrl_of_match[] = {
+	{ .compatible = "usbffff,2", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, apb_ctrl_of_match);
+
+static struct platform_driver apb_ctrl_device_driver = {
+	.probe		= apb_ctrl_probe,
+	.remove		= apb_ctrl_remove,
+	.driver		= {
+		.name	= "unipro-APbridge",
+		.pm	= &apb_ctrl_pm_ops,
+		.of_match_table = of_match_ptr(apb_ctrl_of_match),
+	}
+};
+
+module_platform_driver(apb_ctrl_device_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Vaibhav Hiremath <vaibhav.hiremath@linaro.org>");
+MODULE_DESCRIPTION("AP Bridge Control Driver for DB3 platform");