drivers: Add board uclass

Since there is no canonical "board device" that can be used in board
files, it is difficult to use DM function for board initialization in
these cases.

Hence, add a uclass that implements a simple "board device", which can
hold devices not suitable anywhere else in the device tree, and is also
able to read encoded information, e.g. hard-wired GPIOs on a GPIO
expander, read-only memory ICs, etc. that carry information about the
hardware.

The devices of this uclass expose methods to read generic data types
(integers, strings, booleans) to encode the information provided by the
hardware.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Mario Six <mario.six@gdsys.cc>

drivers/Kconfig

@@ -24,6 +24,8 @@ source "drivers/ddr/Kconfig"
 
 source "drivers/demo/Kconfig"
 
+source "drivers/board/Kconfig"
+
 source "drivers/ddr/fsl/Kconfig"
 
 source "drivers/dfu/Kconfig"

drivers/Makefile

@@ -71,6 +71,7 @@ obj-y += ata/
 obj-$(CONFIG_DM_DEMO) += demo/
 obj-$(CONFIG_BIOSEMU) += bios_emulator/
 obj-y += block/
+obj-y += board/
 obj-$(CONFIG_BOOTCOUNT_LIMIT) += bootcount/
 obj-$(CONFIG_CPU) += cpu/
 obj-y += crypto/

drivers/board/Kconfig

@@ -0,0 +1,7 @@
+menuconfig BOARD
+	bool "Device Information"
+	help
+	  Support methods to query hardware configurations from internal
+	  mechanisms (e.g. reading GPIO values, determining the presence of
+	  devices on busses, etc.). This enables the usage of U-Boot with
+	  modular board architectures.

drivers/board/Makefile

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier:	GPL-2.0+
+#
+# (C) Copyright 2017
+# Mario Six,  Guntermann & Drunck GmbH, mario.six@gdsys.cc
+obj-$(CONFIG_BOARD) += board-uclass.o
+obj-$(CONFIG_BOARD_GAZERBEAM) += gazerbeam.o

drivers/board/board-uclass.c

@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * (C) Copyright 2017
+ * Mario Six,  Guntermann & Drunck GmbH, mario.six@gdsys.cc
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <board.h>
+
+int board_get(struct udevice **devp)
+{
+	return uclass_first_device_err(UCLASS_BOARD, devp);
+}
+
+int board_detect(struct udevice *dev)
+{
+	struct board_ops *ops = board_get_ops(dev);
+
+	if (!ops->detect)
+		return -ENOSYS;
+
+	return ops->detect(dev);
+}
+
+int board_get_bool(struct udevice *dev, int id, bool *val)
+{
+	struct board_ops *ops = board_get_ops(dev);
+
+	if (!ops->get_bool)
+		return -ENOSYS;
+
+	return ops->get_bool(dev, id, val);
+}
+
+int board_get_int(struct udevice *dev, int id, int *val)
+{
+	struct board_ops *ops = board_get_ops(dev);
+
+	if (!ops->get_int)
+		return -ENOSYS;
+
+	return ops->get_int(dev, id, val);
+}
+
+int board_get_str(struct udevice *dev, int id, size_t size, char *val)
+{
+	struct board_ops *ops = board_get_ops(dev);
+
+	if (!ops->get_str)
+		return -ENOSYS;
+
+	return ops->get_str(dev, id, size, val);
+}
+
+UCLASS_DRIVER(board) = {
+	.id		= UCLASS_BOARD,
+	.name		= "board",
+	.post_bind	= dm_scan_fdt_dev,
+};

include/board.h

@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * (C) Copyright 2017
+ * Mario Six,  Guntermann & Drunck GmbH, mario.six@gdsys.cc
+ */
+
+/*
+ * This uclass encapsulates hardware methods to gather information about a
+ * board or a specific device such as hard-wired GPIOs on GPIO expanders,
+ * read-only data in flash ICs, or similar.
+ *
+ * The interface offers functions to read the usual standard data types (bool,
+ * int, string) from the device, each of which is identified by a static
+ * numeric ID (which will usually be defined as a enum in a header file).
+ *
+ * If for example the board had a read-only serial number flash IC, we could
+ * call
+ *
+ * ret = board_detect(dev);
+ * if (ret) {
+ *	debug("board device not found.");
+ *	return ret;
+ * }
+ *
+ * ret = board_get_int(dev, ID_SERIAL_NUMBER, &serial);
+ * if (ret) {
+ *	debug("Error when reading serial number from device.");
+ *	return ret;
+ * }
+ *
+ * to read the serial number.
+ */
+
+struct board_ops {
+	/**
+	 * detect() - Run the hardware info detection procedure for this
+	 *	      device.
+	 * @dev:      The device containing the information
+	 *
+	 * This operation might take a long time (e.g. read from EEPROM,
+	 * check the presence of a device on a bus etc.), hence this is not
+	 * done in the probe() method, but later during operation in this
+	 * dedicated method.
+	 *
+	 * Return: 0 if OK, -ve on error.
+	 */
+	int (*detect)(struct udevice *dev);
+
+	/**
+	 * get_bool() - Read a specific bool data value that describes the
+	 *		hardware setup.
+	 * @dev:	The board instance to gather the data.
+	 * @id:		A unique identifier for the bool value to be read.
+	 * @val:	Pointer to a buffer that receives the value read.
+	 *
+	 * Return: 0 if OK, -ve on error.
+	 */
+	int (*get_bool)(struct udevice *dev, int id, bool *val);
+
+	/**
+	 * get_int() - Read a specific int data value that describes the
+	 *	       hardware setup.
+	 * @dev:       The board instance to gather the data.
+	 * @id:        A unique identifier for the int value to be read.
+	 * @val:       Pointer to a buffer that receives the value read.
+	 *
+	 * Return: 0 if OK, -ve on error.
+	 */
+	int (*get_int)(struct udevice *dev, int id, int *val);
+
+	/**
+	 * get_str() - Read a specific string data value that describes the
+	 *	       hardware setup.
+	 * @dev:	The board instance to gather the data.
+	 * @id:		A unique identifier for the string value to be read.
+	 * @size:	The size of the buffer to receive the string data.
+	 * @val:	Pointer to a buffer that receives the value read.
+	 *
+	 * Return: 0 if OK, -ve on error.
+	 */
+	int (*get_str)(struct udevice *dev, int id, size_t size, char *val);
+};
+
+#define board_get_ops(dev)	((struct board_ops *)(dev)->driver->ops)
+
+/**
+ * board_detect() - Run the hardware info detection procedure for this device.
+ *
+ * @dev:	The device containing the information
+ *
+ * Return: 0 if OK, -ve on error.
+ */
+int board_detect(struct udevice *dev);
+
+/**
+ * board_get_bool() - Read a specific bool data value that describes the
+ *		      hardware setup.
+ * @dev:	The board instance to gather the data.
+ * @id:		A unique identifier for the bool value to be read.
+ * @val:	Pointer to a buffer that receives the value read.
+ *
+ * Return: 0 if OK, -ve on error.
+ */
+int board_get_bool(struct udevice *dev, int id, bool *val);
+
+/**
+ * board_get_int() - Read a specific int data value that describes the
+ *		     hardware setup.
+ * @dev:	The board instance to gather the data.
+ * @id:		A unique identifier for the int value to be read.
+ * @val:	Pointer to a buffer that receives the value read.
+ *
+ * Return: 0 if OK, -ve on error.
+ */
+int board_get_int(struct udevice *dev, int id, int *val);
+
+/**
+ * board_get_str() - Read a specific string data value that describes the
+ *		     hardware setup.
+ * @dev:	The board instance to gather the data.
+ * @id:		A unique identifier for the string value to be read.
+ * @size:	The size of the buffer to receive the string data.
+ * @val:	Pointer to a buffer that receives the value read.
+ *
+ * Return: 0 if OK, -ve on error.
+ */
+int board_get_str(struct udevice *dev, int id, size_t size, char *val);
+
+/**
+ * board_get() - Return the board device for the board in question.
+ * @devp: Pointer to structure to receive the board device.
+ *
+ * Since there can only be at most one board instance, the API can supply a
+ * function that returns the unique device. This is especially useful for use
+ * in board files.
+ *
+ * Return: 0 if OK, -ve on error.
+ */
+int board_get(struct udevice **devp);

include/dm/uclass-id.h

@@ -30,6 +30,7 @@ enum uclass_id {
 	UCLASS_ADC,		/* Analog-to-digital converter */
 	UCLASS_AHCI,		/* SATA disk controller */
 	UCLASS_BLK,		/* Block device */
+	UCLASS_BOARD,		/* Device information from hardware */
 	UCLASS_CLK,		/* Clock source, e.g. used by peripherals */
 	UCLASS_CPU,		/* CPU, typically part of an SoC */
 	UCLASS_CROS_EC,		/* Chrome OS EC */