boards: arty: add support for daplink qspi mux

The ARM Cortex-M1/M3 DesignStart FPGA reference designs support booting
from an off-board, memory-mapped QSPI NOR flash device. The V2C DAPlink
shield from ARM Ltd. provides support for this feature.

If the board/shield is not configured for booting from the QSPI NOR
device, that same device is available as a regular QSPI NOR flash
device.

The presense of a shield configured for QSPI NOR flash boot is indicated
through an IRQ line used as a level-detect, non-interrupt signal.

Introduce a board specific devicetree binding for the DAPLink QSPI MUX
and provide a board specific API accessing it. Automatically set the
QSPI MUX to to provide regular QSPI NOR flash access if the board/shield
is not configured for memory-mapped QSPI NOR flash boot.

Signed-off-by: Henrik Brix Andersen <henrik@brixandersen.dk>

boards/arm/arty/CMakeLists.txt

@@ -1,5 +1,8 @@
 # SPDX-License-Identifier: Apache-2.0
 
+zephyr_library()
+zephyr_library_sources(board.c)
+
 if((CONFIG_BOARD_ARTY_A7_ARM_DESIGNSTART_M1) AND (CONFIG_BUILD_OUTPUT_BIN))
   # Generate zephyr.mem verilog memory hex dump file for initialising ITCM in
   # Xilinx Vivado.

boards/arm/arty/Kconfig

@@ -0,0 +1,13 @@
+# Digilent Arty board configuration
+
+# Copyright (c) 2020 Henrik Brix Andersen <henrik@brixandersen.dk>
+# SPDX-License-Identifier: Apache-2.0
+
+config BOARD_INIT_PRIORITY
+	int "Board initialization priority"
+	default 50
+	depends on BOARD_ARTY_A7_ARM_DESIGNSTART_M1 || BOARD_ARTY_A7_ARM_DESIGNSTART_M3
+	depends on "$(dt_nodelabel_enabled,daplink_qspi_mux)"
+	help
+	  Board initialization priority. The board initialization must take
+	  place after the GPIO driver is initialized.

boards/arm/arty/Kconfig.defconfig

@@ -25,6 +25,9 @@ config UART_XLNX_UARTLITE
 
 endif # SERIAL
 
+config GPIO
+	default y if "$(dt_nodelabel_enabled,daplink_qspi_mux)"
+
 if GPIO
 
 config GPIO_XLNX_AXI

boards/arm/arty/board.c

@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2020 Henrik Brix Andersen <henrik@brixandersen.dk>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <arch/arm/aarch32/cortex_m/cmsis.h>
+#include <device.h>
+#include <devicetree.h>
+#include <drivers/gpio.h>
+#include <init.h>
+#include <logging/log.h>
+LOG_MODULE_REGISTER(board, CONFIG_LOG_DEFAULT_LEVEL);
+
+#include "board.h"
+
+#define DAPLINK_QSPI_MUX_NODE DT_NODELABEL(daplink_qspi_mux)
+
+#if DT_NODE_HAS_STATUS(DAPLINK_QSPI_MUX_NODE, okay)
+int board_daplink_qspi_mux_select(enum board_daplink_qspi_mux_mode mode)
+{
+	const struct device *gpio;
+	gpio_flags_t flags;
+	int err;
+
+	switch (mode) {
+	case BOARD_DAPLINK_QSPI_MUX_MODE_XIP:
+		flags = GPIO_OUTPUT_LOW;
+		break;
+	case BOARD_DAPLINK_QSPI_MUX_MODE_NORMAL:
+		flags = GPIO_OUTPUT_HIGH;
+		break;
+	default:
+		__ASSERT(0, "invalid mode");
+		return -EINVAL;
+	};
+
+	gpio = device_get_binding(DT_GPIO_LABEL(DAPLINK_QSPI_MUX_NODE,
+						mux_gpios));
+	if (!gpio) {
+		LOG_ERR("DAPLink QSPI MUX GPIO device '%s' not found",
+			DT_GPIO_LABEL(DAPLINK_QSPI_MUX_NODE, mux_gpios));
+		return -EINVAL;
+	}
+
+	err = gpio_config(gpio, DT_GPIO_PIN(DAPLINK_QSPI_MUX_NODE, mux_gpios),
+			  DT_GPIO_FLAGS(DAPLINK_QSPI_MUX_NODE, mux_gpios) |
+			  flags);
+	if (err) {
+		LOG_ERR("failed to configure DAPLink QSPI MUX GPIO (err %d)",
+			err);
+		return err;
+	}
+
+	return 0;
+}
+
+bool board_daplink_is_fitted(void)
+{
+	/*
+	 * The DAPLINK_fitted_n signal is routed to an IRQ line. It is used as a
+	 * level-detect non-interrupt signal to determine if the DAPLink shield
+	 * is fitted.
+	 */
+	return !NVIC_GetPendingIRQ(DT_IRQN(DAPLINK_QSPI_MUX_NODE));
+}
+
+static int board_init(const struct device *dev)
+{
+	ARG_UNUSED(dev);
+
+	/*
+	 * Automatically select normal mode unless the DAPLink shield is fitted
+	 * in which case the CPU will have the off-board QSPI NOR flash
+	 * memory-mapped at 0x0.
+	 */
+	if (!board_daplink_is_fitted()) {
+		board_daplink_qspi_mux_select(
+			BOARD_DAPLINK_QSPI_MUX_MODE_NORMAL);
+	}
+
+	return 0;
+}
+
+SYS_INIT(board_init, POST_KERNEL, CONFIG_BOARD_INIT_PRIORITY);
+#endif /* DT_NODE_HAS_STATUS(DAPLINK_QSPI_MUX_NODE, okay) */

boards/arm/arty/board.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2020 Henrik Brix Andersen <henrik@brixandersen.dk>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef __INC_BOARD_H
+#define __INC_BOARD_H
+
+enum board_daplink_qspi_mux_mode {
+	/* eXecute-In-Place mode */
+	BOARD_DAPLINK_QSPI_MUX_MODE_XIP,
+	/* Normal mode */
+	BOARD_DAPLINK_QSPI_MUX_MODE_NORMAL,
+};
+
+/**
+ * @brief Select the mode of the DAPlink QSPI multiplexer.
+ *
+ * Note: The multiplexer mode must not be changed while executing code from the
+ *       off-board QSPI flash in XIP mode.
+ *
+ * @param mode The multiplexer mode to be selected.
+ *
+ * @retval 0 If successful, negative errno otherwise.
+ */
+int board_daplink_qspi_mux_select(enum board_daplink_qspi_mux_mode mode);
+
+/**
+ * @brief Determine if the DAPlink shield is fitted.
+ *
+ * Determine if the DAPlink shield is fitted based on the state of the
+ * DAPLINK_fitted_n signal.
+ *
+ * @retval true If the DAPlink shield is fitted.
+ * @retval false If the DAPlink shield is not fitted.
+ */
+bool board_daplink_is_fitted(void);
+
+#endif /* __INC_BOARD_H */

boards/arm/arty/dts/arty_a7_arm_designstart.dtsi

@@ -135,7 +135,31 @@
 		};
 	};
 
+	daplink_qspi_mux: daplink_qspi_mux {
+		compatible = "arm,daplink-qspi-mux";
+		status = "disabled";
+		interrupt-parent = <&nvic>;
+		interrupts = <7 0>;
+		mux-gpios = <&daplink_gpio0 0 GPIO_ACTIVE_HIGH>;
+	};
+
 	soc {
+		daplink_gpio0: gpio@40010000 {
+			compatible = "xlnx,xps-gpio-1.00.a";
+			status = "disabled";
+			reg = <0x40010000 0x10000>;
+			label = "DAPLINK_GPIO_0";
+			gpio-controller;
+			#gpio-cells = <2>;
+
+			xlnx,all-inputs = <0x0>;
+			xlnx,all-outputs = <0x0>;
+			xlnx,dout-default = <0x0>;
+			xlnx,gpio-width = <0x20>;
+			xlnx,is-dual = <0x0>;
+			xlnx,tri-default = <0xffffffff>;
+		};
+
 		daplink_quad_spi0: spi@40020000 {
 			compatible = "xlnx,xps-spi-2.00.a";
 			status = "disabled";

boards/arm/arty/dts/bindings/arm,daplink-qspi-mux.yaml

@@ -0,0 +1,21 @@
+# Copyright (c) 2020 Henrik Brix Andersen <henrik@brixandersen.dk>
+# SPDX-License-Identifier: Apache-2.0
+
+description: ARM DesignStart FPGA DAPLink QSPI bus multiplexer
+
+compatible: "arm,daplink-qspi-mux"
+
+include: base.yaml
+
+properties:
+    interrupts:
+      required: true
+      description: |
+        IRQ line connected to the level-detect non-interrupt DAPLink shield
+        fitted signal
+
+    mux-gpios:
+      type: phandle-array
+      required: true
+      description: |
+        GPIO for controlling the DAPLink QSPI bus multiplexer