Date:   Thu,  2 Aug 2018 21:45:33 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Noralf T <noralf@...nnes.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Cc:     Sam Ravnborg <sam@...nborg.org>
Subject: [PATCH v1 2/5] pardata: new bus for parallel data access

The pardata supports implement a simple bus for devices
that are connected using a parallel bus driven by GPIOs.
The is often used in combination with simple displays
that is often seen in older embedded designs.
There is a demand for this support also in the linux
kernel for HW designs that uses these kind of displays.

The pardata bus uses a platfrom_driver that when probed
creates devices for all child nodes in the DT,
which are then supposed to be handled by pardata_drivers.

Signed-off-by: Sam Ravnborg <sam@...nborg.org>
---
 Documentation/driver-api/index.rst   |   1 +
 Documentation/driver-api/pardata.rst |  60 ++++++++
 MAINTAINERS                          |   9 ++
 drivers/Kconfig                      |   2 +
 drivers/Makefile                     |   1 +
 drivers/pardata/Kconfig              |  17 +++
 drivers/pardata/Makefile             |   5 +
 drivers/pardata/pardata.c            | 282 +++++++++++++++++++++++++++++++++++
 include/linux/pardata.h              | 138 +++++++++++++++++
 9 files changed, 515 insertions(+)
 create mode 100644 Documentation/driver-api/pardata.rst
 create mode 100644 drivers/pardata/Kconfig
 create mode 100644 drivers/pardata/Makefile
 create mode 100644 drivers/pardata/pardata.c
 create mode 100644 include/linux/pardata.h

diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst
index 6d9f2f9fe20e..1808fca406ae 100644
--- a/Documentation/driver-api/index.rst
+++ b/Documentation/driver-api/index.rst
@@ -41,6 +41,7 @@ available subsections can be seen below.
    miscellaneous
    w1
    rapidio
+   pardata
    s390-drivers
    vme
    80211/index
diff --git a/Documentation/driver-api/pardata.rst b/Documentation/driver-api/pardata.rst
new file mode 100644
index 000000000000..a811f024a0fe
--- /dev/null
+++ b/Documentation/driver-api/pardata.rst
@@ -0,0 +1,60 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================
+Parallel Data Bus/Drivers
+=========================
+
+Displays may be connected using a simple parallel bus.
+This is often seen in embedded systems with a simple MCU, but is also
+used in Linux based systems to a small extent.
+
+The bus looks like this:
+
+.. code-block:: none
+
+       ----+
+           |  DB0-DB7 or DB4-DB7      +----
+           ===/========================
+           |  E - enable              |  D
+           ----------------------------  I
+        C  |  Reset                   |  S
+        P  ----------------------------  P
+        U  |  Read/Write (one or two) |  L
+           ----------------------------  A
+           |  RS - instruction/data   |  Y
+           ----------------------------
+           |                          +----
+       ----+
+
+There may be several devices connected to the bus with individual
+reset and read/write signals.
+Two types of interfaces are supported. 8800 with a single read/write signal,
+and 6800 with individual read/write signals.
+
+Display supported by the parallel data bus: `<https://www.sparkfun.com/products/710>`_
+
+The overall code structure is
+
+.. code-block:: none
+
+  platform_device [pardata bus]   <--- pardatabus [driver]
+       |
+       +-> device
+             |
+             +-> pardata_bus_data
+
+  pardata_device
+      |
+      +-> device
+            |
+            +->
+
+  pardatabus_bus
+
+
+API documentation
+=================
+.. kernel-doc:: include/linux/pardata.h
+   :internal:
+.. kernel-doc:: drivers/pardata/pardata.c
+   :internal:
diff --git a/MAINTAINERS b/MAINTAINERS
index 96e98e206b0d..4ba7ff7c3e46 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -10727,6 +10727,15 @@ L:	platform-driver-x86@...r.kernel.org
 S:	Maintained
 F:	drivers/platform/x86/panasonic-laptop.c
 
+PARALLEL DATA SUBSYSTEM
+M:	Sam Ravnborg <sam@...nborg.org>
+S:	Maintained
+F:	drivers/pardata/
+F:	include/linux/pardata.h
+F:	drivers/gpu/drm/tinydrm/pardata-dbi.c
+F:	include/drm/pardata-dbi.h
+F:	Documentation/driver-api/pardata.rst
+
 PARALLEL LCD/KEYPAD PANEL DRIVER
 M:	Willy Tarreau <willy@...roxy.com>
 M:	Ksenija Stanojevic <ksenija.stanojevic@...il.com>
diff --git a/drivers/Kconfig b/drivers/Kconfig
index 95b9ccc08165..b51b25aae9a5 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -217,4 +217,6 @@ source "drivers/siox/Kconfig"
 
 source "drivers/slimbus/Kconfig"
 
+source "drivers/pardata/Kconfig"
+
 endmenu
diff --git a/drivers/Makefile b/drivers/Makefile
index 24cd47014657..cfe7945f2f6b 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -67,6 +67,7 @@ obj-$(CONFIG_CONNECTOR)		+= connector/
 obj-$(CONFIG_FB_I810)           += video/fbdev/i810/
 obj-$(CONFIG_FB_INTEL)          += video/fbdev/intelfb/
 
+obj-$(CONFIG_PARDATA)		+= pardata/
 obj-$(CONFIG_PARPORT)		+= parport/
 obj-$(CONFIG_NVM)		+= lightnvm/
 obj-y				+= base/ block/ misc/ mfd/ nfc/
diff --git a/drivers/pardata/Kconfig b/drivers/pardata/Kconfig
new file mode 100644
index 000000000000..5a4280a3f85a
--- /dev/null
+++ b/drivers/pardata/Kconfig
@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Parallel Data Bus framework
+#
+menuconfig PARDATA
+	tristate "Parallel Data support"
+	help
+	  The parallel data framework is used for devices communicating
+	  with a simple parallel interface.
+	  The interface include 8 data pins, one register select,
+	  one enable pin, a chip select and a reset pin.
+	  The read/write may be 8080 style (one r/w pin) or 6800 style
+	  with separate read and write pins.
+	  The parallel data bus is often used for displays in embedded
+	  systems.
+
+	  If unsure, choose N.
diff --git a/drivers/pardata/Makefile b/drivers/pardata/Makefile
new file mode 100644
index 000000000000..0e48bd648879
--- /dev/null
+++ b/drivers/pardata/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for kernel Parallel Data subsystem
+#
+obj-$(CONFIG_PARDATA) += pardata.o
diff --git a/drivers/pardata/pardata.c b/drivers/pardata/pardata.c
new file mode 100644
index 000000000000..985d692c116a
--- /dev/null
+++ b/drivers/pardata/pardata.c
@@ -0,0 +1,282 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2018, Sam Ravnborg
+ *
+ * Author: Sam Ravnborg <sam@...nborg.org>
+ */
+
+/**
+ * DOC: Bus driver for parallel data bus
+ *
+ * The parallel data bus is often used for displays
+ * in embedded designs and is sometimes also used
+ * in designs supporting Linux.
+ */
+
+#include <linux/platform_device.h>
+#include <linux/gpio/consumer.h>
+#include <linux/of_device.h>
+#include <linux/pardata.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/of.h>
+
+static struct pardata_device *
+pardata_device_create(struct pardatabus_data *pdbus)
+{
+	struct pardata_device *pddev;
+
+	/* We allocate the device, and initialize the default values */
+	pddev = kzalloc(sizeof(*pddev), GFP_KERNEL);
+	if (!pddev)
+		return ERR_PTR(-ENOMEM);
+
+	pddev->dev.parent = pdbus->dev;
+	pddev->dev.bus = &pardata_bus;
+
+	dev_set_name(&pddev->dev, "pardata");
+
+	device_initialize(&pddev->dev);
+
+	return pddev;
+}
+
+static void pardata_device_release(struct pardata_device *ppdev)
+{
+	kfree(ppdev);
+}
+
+int pardata_device_register(struct pardata_device *pddev)
+{
+	return device_add(&pddev->dev);
+}
+
+static int of_pdbus_register_device(struct pardatabus_data *pdbus,
+				    struct device_node *np)
+{
+	struct pardata_device *pddev;
+	int ret;
+	u32 id;
+
+	pddev = pardata_device_create(pdbus);
+	if (IS_ERR(pddev))
+		return PTR_ERR(pddev);
+
+	/* The reg property is used as id */
+	ret = of_property_read_u32(np, "reg", &id);
+	if (ret) {
+		dev_err(pdbus->dev, "Failed to read the 'reg' property");
+		pardata_device_release(pddev);
+		return ret;
+	}
+	pddev->id = id;
+
+	/*
+	 *  Associate the OF node with the device structure so it
+	 * can be looked up later.
+	 */
+	of_node_get(np);
+	pddev->dev.of_node = np;
+
+	/* All data is now stored in the pardata_device struct; register it. */
+	ret = pardata_device_register(pddev);
+	if (ret) {
+		pardata_device_release(pddev);
+		of_node_put(np);
+		return ret;
+	}
+
+	dev_dbg(&pddev->dev, "registered pardata device %s with id %i\n",
+		np->name, id);
+	return 0;
+}
+
+static void pdbus_unregister(void)
+{
+	bus_unregister(&pardata_bus);
+}
+
+/**
+ * of_pardata_register - Register pardatabus and create devices from DT
+ *
+ * @pdbus: pointer to pardatabus_data structure
+ *
+ * This function registers the pardatabus_data structure and registers
+ * a pardata_device for each child node of @np.
+ */
+int of_pardata_register(struct pardatabus_data *pdbus)
+{
+	struct device_node *child;
+	struct device_node *np;
+	int ret;
+
+	np = pdbus->dev->of_node;
+
+	/* Do not continue if the node is not available or disabled */
+	if (!np || !of_device_is_available(np))
+		return -ENODEV;
+
+	/* Register the parallel data bus */
+	ret = bus_register(&pardata_bus);
+	if (ret)
+		return ret;
+
+	/*
+	 * Loop over the child nodes and register a
+	 * pardata_device for each node
+	 */
+	for_each_available_child_of_node(np, child) {
+		ret = of_pdbus_register_device(pdbus, child);
+
+		if (ret == -ENODEV)
+			dev_err(pdbus->dev, "pardata device missing.\n");
+		else if (ret)
+			goto unregister;
+	}
+	return 0;
+
+unregister:
+	pdbus_unregister();
+	return ret;
+}
+
+static int pardata_device_match(struct device *dev, struct device_driver *drv)
+{
+	/* OF style match */
+	if (of_match_device(drv->of_match_table, dev) != NULL)
+		return 1;
+
+	return 0;
+}
+
+static int pardata_device_probe(struct device *dev)
+{
+	struct pardata_device *pddev;
+	struct pardata_driver *pddrv;
+
+	pddev = to_pardata_device(dev);
+	pddrv = to_pardata_driver(dev->driver);
+
+	return pddrv->probe(pddev);
+}
+
+struct bus_type pardata_bus = {
+	.name		= "pardata",
+	.match		= pardata_device_match,
+	.probe		= pardata_device_probe,
+};
+EXPORT_SYMBOL_GPL(pardata_bus);
+
+/*
+ * __pardata_driver_register() - Client driver registration
+ *
+ * @drv:Client driver to be associated with client-device.
+ * @owner: owning module/driver
+ *
+ * Do not call this direct, use pardata_driver_register()
+ */
+int __pardata_driver_register(struct pardata_driver *drv, struct module *owner)
+{
+	/* probe is mandatory */
+	if (!drv->probe)
+		return -EINVAL;
+
+	drv->driver.bus = &pardata_bus;
+	drv->driver.owner = owner;
+
+	return driver_register(&drv->driver);
+}
+EXPORT_SYMBOL_GPL(__pardata_driver_register);
+
+/*
+ * Use a simple pardatabus driver to create the pardata
+ * devices from child nodes in DT.
+ *
+ * The pardatabus driver parses the properties in the
+ * device tree that will be used by the pardata drivers.
+ */
+static int pardatabus_probe(struct platform_device *pdev)
+{
+	struct pardatabus_data *pdbus;
+	struct gpio_descs *pins;
+	struct gpio_desc *pin;
+	struct device *dev;
+
+	dev = &pdev->dev;
+
+	pdbus = devm_kzalloc(dev, sizeof(*pdbus), GFP_KERNEL);
+	if (!pdbus)
+		return -ENOMEM;
+
+	pdbus->dev = &pdev->dev;
+	dev_set_drvdata(dev, pdbus);
+
+	/* Get the mandatory bus details from DT */
+	pins = devm_gpiod_get_array(dev, "data-gpios", GPIOD_OUT_LOW);
+	if (IS_ERR(pins)) {
+		dev_err(dev, "Failed to get gpio 'data-gpios'");
+		return PTR_ERR(pins);
+	}
+	if (pins->ndescs != 4 && pins->ndescs != 8) {
+		dev_err(dev, "Invalid number of data-gpios %d - expected 4 or 8\n",
+			    pins->ndescs);
+		return -EINVAL;
+	}
+	pdbus->data_pins = pins;
+
+	pin = devm_gpiod_get(dev, "enable-gpios", GPIOD_OUT_LOW);
+	if (IS_ERR(pin)) {
+		dev_err(dev, "Failed to get gpio 'enable-gpios'\n");
+		return PTR_ERR(pin);
+	}
+	pdbus->pin_enable = pin;
+
+	pin = devm_gpiod_get(dev, "rs-gpios", GPIOD_OUT_HIGH);
+	if (IS_ERR(pin)) {
+		dev_err(dev, "Failed to get gpio 'rs-gpios'\n");
+		return PTR_ERR(pin);
+	}
+	pdbus->pin_rs = pin;
+
+	pin = devm_gpiod_get(dev, "rw-gpios", GPIOD_OUT_HIGH);
+	if (IS_ERR(pin)) {
+		dev_err(dev, "Failed to get gpio 'rw-gpios'\n");
+		return PTR_ERR(pin);
+	}
+	pdbus->pin_readwrite = pin;
+
+	pin = devm_gpiod_get(dev, "read-gpios", GPIOD_OUT_HIGH);
+	if (IS_ERR(pin)) {
+		dev_err(dev, "Failed to get gpio 'read-gpios'\n");
+		return PTR_ERR(pin);
+	}
+	pdbus->pin_read = pin;
+
+	pin = devm_gpiod_get(dev, "write-gpios", GPIOD_OUT_HIGH);
+	if (IS_ERR(pin)) {
+		dev_err(dev, "Failed to get gpio 'write-gpios'\n");
+		return PTR_ERR(pin);
+	}
+	pdbus->pin_write = pin;
+
+	return of_pardata_register(pdbus);
+}
+
+static const struct of_device_id pardata_bus_dt_ids[] = {
+	{ .compatible = "parallel-data-bus", },
+	{ /* sentinel */ }
+};
+
+static struct platform_driver pardatabus_driver = {
+	.driver	 = {
+		.name   = "pardatabus",
+		.of_match_table = pardata_bus_dt_ids,
+	},
+	.probe = pardatabus_probe,
+};
+module_platform_driver(pardatabus_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("Parallel Data Bus");
diff --git a/include/linux/pardata.h b/include/linux/pardata.h
new file mode 100644
index 000000000000..888a1c88176e
--- /dev/null
+++ b/include/linux/pardata.h
@@ -0,0 +1,138 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2018 Sam Ravnborg
+ */
+
+#ifndef _LINUX_PARDATA_H
+#define _LINUX_PARDATA_H
+
+#include <linux/device.h>
+#include <linux/module.h>
+
+extern struct bus_type pardata_bus;
+
+/**
+ * struct pardatabus_data - private data for the pardata bus
+ *
+ * Drivers uses these data when usung the pins that are part of
+ * the bus.
+ */
+struct pardatabus_data {
+	/**
+	 * @dev: device node that represent the DT node of the bus
+	 */
+	struct device *dev;
+
+	/**
+	 * @data_pins: The 8 or 4 GPIOs used for data
+	 */
+	struct gpio_descs *data_pins;
+
+	/**
+	 * @pin_enable: The enable pin (mandatory)
+	 */
+	struct gpio_desc *pin_enable;
+
+	/**
+	 * @pin_rs: register select (0: instruction 1: data)
+	 */
+	struct gpio_desc *pin_rs;
+
+	/**
+	 * @pin_readwrite: readwrite pin for 8080 style interface
+	 */
+	struct gpio_desc *pin_readwrite;
+
+	/**
+	 * @pin_read: read pin for 6800 style interface
+	 */
+	struct gpio_desc *pin_read;
+
+	/**
+	 * @pin_write: write pin for 6800 style interface
+	 */
+	struct gpio_desc *pin_write;
+};
+
+static inline struct pardatabus_data *to_pardatabus_data(struct device *d)
+{
+	return container_of(d, struct pardatabus_data, dev);
+}
+
+/**
+ * struct pardata_device - pardata device handle.
+ * @dev: Driver model representation of the device.
+ *
+ * This is the device handle returned when a pardata
+ * device is registered.
+ * The id comes from the DT
+ *
+ * @dev: The device
+ * @id: Id of the device (from DT)
+ */
+struct pardata_device {
+	struct device dev;
+	u32	   id;
+};
+
+static inline struct pardata_device *to_pardata_device(struct device *d)
+{
+	return container_of(d, struct pardata_device, dev);
+}
+
+static inline void *pardata_dev_get_drvdata(const struct pardata_device *pdd)
+{
+	return dev_get_drvdata(&pdd->dev);
+}
+
+static inline void pardata_dev_set_drvdata(struct pardata_device *pdd,
+					    void *data)
+{
+	dev_set_drvdata(&pdd->dev, data);
+}
+
+/**
+ * struct pardata_driver - pardata 'generic device'
+ *			(similar to 'spi_device' on SPI)
+ *
+ * @driver: generic device driver
+ *	  pardata drivers must initialize name, owner and of_match_table
+ *	  of this structure
+ * @probe: Binds this driver to a pardata bus.
+ * @shutdown: Standard shutdown callback used during powerdown/halt.
+ */
+struct pardata_driver {
+	struct device_driver driver;
+	int   (*probe)(struct pardata_device *pdd);
+	void  (*shutdown)(struct pardata_device *pdd);
+};
+
+static inline struct pardata_driver *to_pardata_driver(struct device_driver *d)
+{
+	return container_of(d, struct pardata_driver, driver);
+}
+
+/* Use macro for driver registering to get simple access to THIS_MODULE */
+#define pardata_driver_register(drv) \
+	__pardata_driver_register(drv, THIS_MODULE)
+int __pardata_driver_register(struct pardata_driver *drv, struct module *owner);
+
+static inline void pardata_driver_unregister(struct pardata_driver *drv)
+{
+	return driver_unregister(&drv->driver);
+}
+
+/**
+ * module_pardata_driver() - Helper macro for registering a parallel data driver
+ * @__pardata_driver: pardatabus_driver struct
+ *
+ * Helper macro for parallel data drivers which do not do anything special in
+ * module init/exit. This eliminates a lot of boilerplate. Each module may
+ * only use this macro once, and calling it replaces module_init() and
+ * module_exit()
+ */
+#define module_pardata_driver(__pardata_driver) \
+	module_driver(__pardata_driver, pardata_driver_register, \
+			pardata_driver_unregister)
+
+#endif /* _LINUX_PARDATA_H */
-- 
2.12.0

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