[RFC PATCH 1/3] mfd: upboard: Add UP2 platform controller driver

[Javier Arteaga <javier@xxxxxxxxxx>]

UP Squared (UP2) is a x86 SBC from AAEON based on Intel Apollo Lake. It
features a MAX 10 FPGA that routes lines from both SoC and on-board
devices to two I/O headers:

                                +------------------------+
                                | 40-pin RPi-like header |
                         +------|         (HAT)          |
                         |      +------------------------+
    +-------+    +--------+
    |       |    |        |     +------------------------+
    |  SoC  |----|  FPGA  |-----|  Custom UP2 pin header |
    |       |    |        |     |        (EXHAT)         |
    +-------+    +--------+     +------------------------+
                         |
                         +------* On-board devices: LED, VLS...

This is intended to enable vendor-specific applications to customize I/O
header pinout, as well as include low-latency functionality. It also
performs voltage level translation between the SoC (1.8V) and HAT header
(3.3V).

Out of the box, this block implements a platform controller with a
GPIO-bitbanged control interface. It's enumerated by ACPI and provides
registers to control:

- Configuration of all FPGA-routed header lines. These can be driven
  SoC-to-header, header-to-SoC or set in high impedance.

- On-board LEDs and enable lines for other platform devices.

Add core support for this platform controller as a MFD device, exposing
these registers as a regmap.

Signed-off-by: Javier Arteaga <javier@xxxxxxxxxx>
---
 drivers/mfd/Kconfig         |  17 +++
 drivers/mfd/Makefile        |   1 +
 drivers/mfd/upboard.c       | 253 ++++++++++++++++++++++++++++++++++++
 include/linux/mfd/upboard.h |  65 +++++++++
 4 files changed, 336 insertions(+)
 create mode 100644 drivers/mfd/upboard.c
 create mode 100644 include/linux/mfd/upboard.h

diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index b860eb5aa194..d72927601fa2 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -1812,6 +1812,23 @@ config MFD_STM32_TIMERS
 	  for PWM and IIO Timer. This driver allow to share the
 	  registers between the others drivers.
 
+config MFD_UPBOARD
+	tristate "UP Squared"
+	depends on ACPI
+	depends on GPIOLIB
+	select MFD_CORE
+	select REGMAP
+	help
+	  If you say yes here you get support for the platform controller
+	  of the UP Squared single-board computer.
+
+	  This driver provides common support for accessing the device,
+	  additional drivers must be enabled in order to use the
+	  functionality of the device.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called upboard.
+
 menu "Multimedia Capabilities Port drivers"
 	depends on ARCH_SA1100
 
diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
index d9d2cf0d32ef..ea5b29167a80 100644
--- a/drivers/mfd/Makefile
+++ b/drivers/mfd/Makefile
@@ -229,3 +229,4 @@ obj-$(CONFIG_MFD_MXS_LRADC)     += mxs-lradc.o
 obj-$(CONFIG_MFD_SC27XX_PMIC)	+= sprd-sc27xx-spi.o
 obj-$(CONFIG_RAVE_SP_CORE)	+= rave-sp.o
 
+obj-$(CONFIG_MFD_UPBOARD)  += upboard.o
diff --git a/drivers/mfd/upboard.c b/drivers/mfd/upboard.c
new file mode 100644
index 000000000000..8bae450cb83d
--- /dev/null
+++ b/drivers/mfd/upboard.c
@@ -0,0 +1,253 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * UP Board platform controller driver
+ *
+ * Copyright (c) 2018, Emutex Ltd.
+ *
+ * Author: Javier Arteaga <javier@xxxxxxxxxx>
+ */
+
+#include <linux/acpi.h>
+#include <linux/gpio/consumer.h>
+#include <linux/kernel.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/upboard.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+static int upboard_read(void *context, unsigned int reg, unsigned int *val)
+{
+	const struct upboard * const upboard = context;
+	int i;
+
+	gpiod_set_value(upboard->clear_gpio, 0);
+	gpiod_set_value(upboard->clear_gpio, 1);
+
+	reg |= UPBOARD_READ_FLAG;
+
+	for (i = UPBOARD_ADDRESS_SIZE; i >= 0; i--) {
+		gpiod_set_value(upboard->strobe_gpio, 0);
+		gpiod_set_value(upboard->datain_gpio, (reg >> i) & 0x1);
+		gpiod_set_value(upboard->strobe_gpio, 1);
+	}
+
+	gpiod_set_value(upboard->strobe_gpio, 0);
+	*val = 0;
+
+	for (i = UPBOARD_REGISTER_SIZE - 1; i >= 0; i--) {
+		gpiod_set_value(upboard->strobe_gpio, 1);
+		gpiod_set_value(upboard->strobe_gpio, 0);
+		*val |= gpiod_get_value(upboard->dataout_gpio) << i;
+	}
+
+	gpiod_set_value(upboard->strobe_gpio, 1);
+
+	return 0;
+};
+
+static int upboard_write(void *context, unsigned int reg, unsigned int val)
+{
+	const struct upboard * const upboard = context;
+	int i;
+
+	gpiod_set_value(upboard->clear_gpio, 0);
+	gpiod_set_value(upboard->clear_gpio, 1);
+
+	for (i = UPBOARD_ADDRESS_SIZE; i >= 0; i--) {
+		gpiod_set_value(upboard->strobe_gpio, 0);
+		gpiod_set_value(upboard->datain_gpio, (reg >> i) & 0x1);
+		gpiod_set_value(upboard->strobe_gpio, 1);
+	}
+
+	gpiod_set_value(upboard->strobe_gpio, 0);
+
+	for (i = UPBOARD_REGISTER_SIZE - 1; i >= 0; i--) {
+		gpiod_set_value(upboard->datain_gpio, (val >> i) & 0x1);
+		gpiod_set_value(upboard->strobe_gpio, 1);
+		gpiod_set_value(upboard->strobe_gpio, 0);
+	}
+
+	gpiod_set_value(upboard->strobe_gpio, 1);
+
+	return 0;
+};
+
+struct upboard_data {
+	const struct regmap_config *regmapconf;
+	const struct mfd_cell *cells;
+	size_t ncells;
+};
+
+/* UP Squared */
+
+static const struct regmap_range upboard_up2_readable_ranges[] = {
+	regmap_reg_range(UPBOARD_REG_PLATFORM_ID, UPBOARD_REG_FIRMWARE_ID),
+	regmap_reg_range(UPBOARD_REG_FUNC_EN0, UPBOARD_REG_FUNC_EN1),
+	regmap_reg_range(UPBOARD_REG_GPIO_EN0, UPBOARD_REG_GPIO_EN2),
+	regmap_reg_range(UPBOARD_REG_GPIO_DIR0, UPBOARD_REG_GPIO_DIR2),
+};
+
+static const struct regmap_range upboard_up2_writable_ranges[] = {
+	regmap_reg_range(UPBOARD_REG_FUNC_EN0, UPBOARD_REG_FUNC_EN1),
+	regmap_reg_range(UPBOARD_REG_GPIO_EN0, UPBOARD_REG_GPIO_EN2),
+	regmap_reg_range(UPBOARD_REG_GPIO_DIR0, UPBOARD_REG_GPIO_DIR2),
+};
+
+static const struct regmap_access_table upboard_up2_readable_table = {
+	.yes_ranges = upboard_up2_readable_ranges,
+	.n_yes_ranges = ARRAY_SIZE(upboard_up2_readable_ranges),
+};
+
+static const struct regmap_access_table upboard_up2_writable_table = {
+	.yes_ranges = upboard_up2_writable_ranges,
+	.n_yes_ranges = ARRAY_SIZE(upboard_up2_writable_ranges),
+};
+
+static const struct regmap_config upboard_up2_regmap_config = {
+	.reg_bits = UPBOARD_ADDRESS_SIZE,
+	.val_bits = UPBOARD_REGISTER_SIZE,
+	.max_register = UPBOARD_REG_MAX,
+	.reg_read = upboard_read,
+	.reg_write = upboard_write,
+	.fast_io = false,
+	.cache_type = REGCACHE_RBTREE,
+	.rd_table = &upboard_up2_readable_table,
+	.wr_table = &upboard_up2_writable_table,
+};
+
+static const struct mfd_cell upboard_up2_mfd_cells[] = {
+};
+
+static const struct upboard_data upboard_up2_data = {
+	.regmapconf = &upboard_up2_regmap_config,
+	.cells = upboard_up2_mfd_cells,
+	.ncells = ARRAY_SIZE(upboard_up2_mfd_cells),
+};
+
+static int upboard_init_gpio(struct upboard *upboard)
+{
+	struct gpio_desc *enable_gpio;
+
+	enable_gpio = devm_gpiod_get(upboard->dev, "enable", GPIOD_OUT_LOW);
+	if (IS_ERR(enable_gpio))
+		return PTR_ERR(enable_gpio);
+
+	upboard->clear_gpio = devm_gpiod_get(upboard->dev, "clear", GPIOD_OUT_LOW);
+	if (IS_ERR(upboard->clear_gpio))
+		return PTR_ERR(upboard->clear_gpio);
+
+	upboard->strobe_gpio = devm_gpiod_get(upboard->dev, "strobe", GPIOD_OUT_LOW);
+	if (IS_ERR(upboard->strobe_gpio))
+		return PTR_ERR(upboard->strobe_gpio);
+
+	upboard->datain_gpio = devm_gpiod_get(upboard->dev, "datain", GPIOD_OUT_LOW);
+	if (IS_ERR(upboard->datain_gpio))
+		return PTR_ERR(upboard->datain_gpio);
+
+	upboard->dataout_gpio = devm_gpiod_get(upboard->dev, "dataout", GPIOD_IN);
+	if (IS_ERR(upboard->dataout_gpio))
+		return PTR_ERR(upboard->dataout_gpio);
+
+	gpiod_set_value(enable_gpio, 1);
+
+	return 0;
+}
+
+static int upboard_check_supported(struct upboard *upboard)
+{
+	const unsigned int AAEON_MANUFACTURER_ID = 0x01;
+	const unsigned int SUPPORTED_FW_MAJOR = 0x0;
+	unsigned int platform_id, manufacturer_id;
+	unsigned int firmware_id, build, major, minor, patch;
+	int ret;
+
+	ret = regmap_read(upboard->regmap, UPBOARD_REG_PLATFORM_ID, &platform_id);
+	if (ret)
+		return ret;
+
+	manufacturer_id = platform_id & 0xff;
+	if (manufacturer_id != AAEON_MANUFACTURER_ID) {
+		dev_dbg(upboard->dev,
+			"unsupported FPGA firmware from manufacturer 0x%02x",
+			manufacturer_id);
+		return -ENODEV;
+	}
+
+	ret = regmap_read(upboard->regmap, UPBOARD_REG_FIRMWARE_ID, &firmware_id);
+	if (ret)
+		return ret;
+
+	build = (firmware_id >> 12) & 0xf;
+	major = (firmware_id >> 8) & 0xf;
+	minor = (firmware_id >> 4) & 0xf;
+	patch = firmware_id & 0xf;
+	if (major != SUPPORTED_FW_MAJOR) {
+		dev_dbg(upboard->dev, "unsupported FPGA firmware v%u.%u.%u.%u",
+			major, minor, patch, build);
+		return -ENODEV;
+	}
+
+	dev_dbg(upboard->dev, "supported FPGA firmware v%u.%u.%u.%u",
+		major, minor, patch, build);
+	return 0;
+}
+
+static const struct acpi_device_id upboard_acpi_match[] = {
+	{ "AANT0F01", (kernel_ulong_t) &upboard_up2_data },
+	{ }
+};
+MODULE_DEVICE_TABLE(acpi, upboard_acpi_match);
+
+static int upboard_probe(struct platform_device *pdev)
+{
+	struct upboard *upboard;
+	const struct acpi_device_id *id;
+	const struct upboard_data *upboard_data;
+	int ret;
+
+	id = acpi_match_device(upboard_acpi_match, &pdev->dev);
+	if (!id)
+		return -ENODEV;
+
+	upboard_data = (const struct upboard_data *) id->driver_data;
+
+	upboard = devm_kzalloc(&pdev->dev, sizeof(*upboard), GFP_KERNEL);
+	if (!upboard)
+		return -ENOMEM;
+
+	dev_set_drvdata(&pdev->dev, upboard);
+	upboard->dev = &pdev->dev;
+	upboard->regmap = devm_regmap_init(&pdev->dev, NULL, upboard,
+					   upboard_data->regmapconf);
+	if (IS_ERR(upboard->regmap))
+		return PTR_ERR(upboard->regmap);
+
+	ret = upboard_init_gpio(upboard);
+	if (ret && ret != -EPROBE_DEFER)
+		dev_err(&pdev->dev, "failed to init controller GPIOs: %d", ret);
+	if (ret)
+		return ret;
+
+	ret = upboard_check_supported(upboard);
+	if (ret)
+		return ret;
+
+	return devm_mfd_add_devices(&pdev->dev, PLATFORM_DEVID_AUTO,
+				    upboard_data->cells, upboard_data->ncells,
+				    NULL, 0, NULL);
+}
+
+static struct platform_driver upboard_driver = {
+	.probe = upboard_probe,
+	.driver = {
+		.name = "upboard",
+		.acpi_match_table = upboard_acpi_match,
+	},
+};
+
+module_platform_driver(upboard_driver);
+
+MODULE_AUTHOR("Javier Arteaga <javier@xxxxxxxxxx>");
+MODULE_DESCRIPTION("UP Board platform controller driver");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/mfd/upboard.h b/include/linux/mfd/upboard.h
new file mode 100644
index 000000000000..d9dd214f4d29
--- /dev/null
+++ b/include/linux/mfd/upboard.h
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * UP Board MFD driver interface
+ *
+ * Copyright (c) 2018, Emutex Ltd.
+ *
+ * Author: Javier Arteaga <javier@xxxxxxxxxx>
+ */
+
+#ifndef __LINUX_MFD_UPBOARD_H
+#define __LINUX_MFD_UPBOARD_H
+
+#define UPBOARD_ADDRESS_SIZE  7
+#define UPBOARD_REGISTER_SIZE 16
+#define UPBOARD_READ_FLAG     BIT(UPBOARD_ADDRESS_SIZE)
+
+/**
+ * enum upboard_reg - addresses for 16-bit controller registers
+ *
+ * @UPBOARD_REG_PLATFORM_ID:    [RO] BOARD_ID | MANUFACTURER_ID
+ * @UPBOARD_REG_FIRMWARE_ID:    [RO] BUILD | MAJOR | MINOR | PATCH
+ * @UPBOARD_REG_FUNC_EN0:       [RW] Toggles for board functions (bank 0)
+ * @UPBOARD_REG_FUNC_EN1:       [RW] Toggles for board functions (bank 1)
+ * @UPBOARD_REG_GPIO_EN0:       [RW] Hi-Z (0) / enabled (1) GPIO (bank 0)
+ * @UPBOARD_REG_GPIO_EN1:       [RW] Hi-Z (0) / enabled (1) GPIO (bank 1)
+ * @UPBOARD_REG_GPIO_EN2:       [RW] Hi-Z (0) / enabled (1) GPIO (bank 2)
+ * @UPBOARD_REG_GPIO_DIR0:      [RW] SoC- (0) / FPGA- (1) driven GPIO (bank 0)
+ * @UPBOARD_REG_GPIO_DIR1:      [RW] SoC- (0) / FPGA- (1) driven GPIO (bank 1)
+ * @UPBOARD_REG_GPIO_DIR2:      [RW] SoC- (0) / FPGA- (1) driven GPIO (bank 2)
+ * @UPBOARD_REG_MAX: one past the last valid address
+ */
+enum upboard_reg {
+	UPBOARD_REG_PLATFORM_ID   = 0x10,
+	UPBOARD_REG_FIRMWARE_ID   = 0x11,
+	UPBOARD_REG_FUNC_EN0      = 0x20,
+	UPBOARD_REG_FUNC_EN1      = 0x21,
+	UPBOARD_REG_GPIO_EN0      = 0x30,
+	UPBOARD_REG_GPIO_EN1      = 0x31,
+	UPBOARD_REG_GPIO_EN2      = 0x32,
+	UPBOARD_REG_GPIO_DIR0     = 0x40,
+	UPBOARD_REG_GPIO_DIR1     = 0x41,
+	UPBOARD_REG_GPIO_DIR2     = 0x42,
+	UPBOARD_REG_MAX,
+};
+
+/**
+ * struct upboard - internal data shared by the UP MFD and its child drivers
+ *
+ * @dev: pointer to the MFD device
+ * @regmap: pointer to the regmap of 16-bit control registers
+ * @clear_gpio: descriptor for the CLEAR line on the controller
+ * @strobe_gpio: descriptor for the STROBE line on the controller
+ * @datain_gpio: descriptor for the DATAIN line on the controller
+ * @dataout_gpio: descriptor for the DATAOUT line on the controller
+ */
+struct upboard {
+	struct device *dev;
+	struct regmap *regmap;
+	struct gpio_desc *clear_gpio;
+	struct gpio_desc *strobe_gpio;
+	struct gpio_desc *datain_gpio;
+	struct gpio_desc *dataout_gpio;
+};
+
+#endif /*  __LINUX_MFD_UPBOARD_H */
-- 
2.17.0

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