serial: Add RISC-V HTIF console driver

Quite a few RISC-V emulators and ISS (including Spike) have host
transfer interface (HTIF) based console. This patch adds HTIF
based console driver for RISC-V platforms which depends totally
on DT node for HTIF register base address.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
Reviewed-by: Rick Chen <rick@andestech.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

drivers/serial/Kconfig

@@ -866,6 +866,14 @@ config PXA_SERIAL
 	  If you have a machine based on a Marvell XScale PXA2xx CPU you
 	  can enable its onboard serial ports by enabling this option.
 
+config HTIF_CONSOLE
+	bool "RISC-V HTIF console support"
+	depends on DM_SERIAL && 64BIT
+	help
+	  Select this to enable host transfer interface (HTIF) based serial
+	  console. The HTIF device is quite common in RISC-V emulators and
+	  RISC-V ISS so this driver allows using U-Boot on such platforms.
+
 config SIFIVE_SERIAL
 	bool "SiFive UART support"
 	depends on DM_SERIAL

drivers/serial/Makefile

@@ -73,6 +73,7 @@ obj-$(CONFIG_OWL_SERIAL) += serial_owl.o
 obj-$(CONFIG_OMAP_SERIAL) += serial_omap.o
 obj-$(CONFIG_MTK_SERIAL) += serial_mtk.o
 obj-$(CONFIG_MT7620_SERIAL) += serial_mt7620.o
+obj-$(CONFIG_HTIF_CONSOLE) += serial_htif.o
 obj-$(CONFIG_SIFIVE_SERIAL) += serial_sifive.o
 obj-$(CONFIG_XEN_SERIAL) += serial_xen.o
 

drivers/serial/serial_htif.c

@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2022 Ventana Micro Systems Inc.
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <errno.h>
+#include <fdtdec.h>
+#include <log.h>
+#include <watchdog.h>
+#include <asm/global_data.h>
+#include <asm/io.h>
+#include <linux/compiler.h>
+#include <serial.h>
+#include <linux/err.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+#define HTIF_DATA_BITS		48
+#define HTIF_DATA_MASK		((1ULL << HTIF_DATA_BITS) - 1)
+#define HTIF_DATA_SHIFT		0
+#define HTIF_CMD_BITS		8
+#define HTIF_CMD_MASK		((1ULL << HTIF_CMD_BITS) - 1)
+#define HTIF_CMD_SHIFT		48
+#define HTIF_DEV_BITS		8
+#define HTIF_DEV_MASK		((1ULL << HTIF_DEV_BITS) - 1)
+#define HTIF_DEV_SHIFT		56
+
+#define HTIF_DEV_SYSTEM		0
+#define HTIF_DEV_CONSOLE	1
+
+#define HTIF_CONSOLE_CMD_GETC	0
+#define HTIF_CONSOLE_CMD_PUTC	1
+
+#if __riscv_xlen == 64
+# define TOHOST_CMD(dev, cmd, payload) \
+	(((u64)(dev) << HTIF_DEV_SHIFT) | \
+	 ((u64)(cmd) << HTIF_CMD_SHIFT) | \
+	 (u64)(payload))
+#else
+# define TOHOST_CMD(dev, cmd, payload) ({ \
+	if ((dev) || (cmd)) \
+		__builtin_trap(); \
+	(payload); })
+#endif
+#define FROMHOST_DEV(fromhost_value) \
+	((u64)((fromhost_value) >> HTIF_DEV_SHIFT) & HTIF_DEV_MASK)
+#define FROMHOST_CMD(fromhost_value) \
+	((u64)((fromhost_value) >> HTIF_CMD_SHIFT) & HTIF_CMD_MASK)
+#define FROMHOST_DATA(fromhost_value) \
+	((u64)((fromhost_value) >> HTIF_DATA_SHIFT) & HTIF_DATA_MASK)
+
+struct htif_plat {
+	void *fromhost;
+	void *tohost;
+	int console_char;
+};
+
+static void __check_fromhost(struct htif_plat *plat)
+{
+	u64 fh = readq(plat->fromhost);
+
+	if (!fh)
+		return;
+	writeq(0, plat->fromhost);
+
+	/* this should be from the console */
+	if (FROMHOST_DEV(fh) != HTIF_DEV_CONSOLE)
+		__builtin_trap();
+	switch (FROMHOST_CMD(fh)) {
+	case HTIF_CONSOLE_CMD_GETC:
+		plat->console_char = 1 + (u8)FROMHOST_DATA(fh);
+		break;
+	case HTIF_CONSOLE_CMD_PUTC:
+		break;
+	default:
+		__builtin_trap();
+	}
+}
+
+static void __set_tohost(struct htif_plat *plat,
+			 u64 dev, u64 cmd, u64 data)
+{
+	while (readq(plat->tohost))
+		__check_fromhost(plat);
+	writeq(TOHOST_CMD(dev, cmd, data), plat->tohost);
+}
+
+static int htif_serial_putc(struct udevice *dev, const char ch)
+{
+	struct htif_plat *plat = dev_get_plat(dev);
+
+	__set_tohost(plat, HTIF_DEV_CONSOLE, HTIF_CONSOLE_CMD_PUTC, ch);
+	return 0;
+}
+
+static int htif_serial_getc(struct udevice *dev)
+{
+	int ch;
+	struct htif_plat *plat = dev_get_plat(dev);
+
+	if (plat->console_char < 0)
+		__check_fromhost(plat);
+
+	if (plat->console_char >= 0) {
+		ch = plat->console_char;
+		plat->console_char = -1;
+		__set_tohost(plat, HTIF_DEV_CONSOLE, HTIF_CONSOLE_CMD_GETC, 0);
+		return (ch) ? ch - 1 : -EAGAIN;
+	}
+
+	return -EAGAIN;
+}
+
+static int htif_serial_pending(struct udevice *dev, bool input)
+{
+	struct htif_plat *plat = dev_get_plat(dev);
+
+	if (!input)
+		return 0;
+
+	if (plat->console_char < 0)
+		__check_fromhost(plat);
+
+	return (plat->console_char >= 0) ? 1 : 0;
+}
+
+static int htif_serial_probe(struct udevice *dev)
+{
+	struct htif_plat *plat = dev_get_plat(dev);
+
+	/* Queue first getc request */
+	__set_tohost(plat, HTIF_DEV_CONSOLE, HTIF_CONSOLE_CMD_GETC, 0);
+
+	return 0;
+}
+
+static int htif_serial_of_to_plat(struct udevice *dev)
+{
+	fdt_addr_t addr;
+	struct htif_plat *plat = dev_get_plat(dev);
+
+	addr = dev_read_addr_index(dev, 0);
+	if (addr == FDT_ADDR_T_NONE)
+		return -ENODEV;
+	plat->fromhost = (void *)(uintptr_t)addr;
+	plat->tohost = plat->fromhost + sizeof(u64);
+
+	addr = dev_read_addr_index(dev, 1);
+	if (addr != FDT_ADDR_T_NONE)
+		plat->tohost = (void *)(uintptr_t)addr;
+
+	plat->console_char = -1;
+
+	return 0;
+}
+
+static const struct dm_serial_ops htif_serial_ops = {
+	.putc = htif_serial_putc,
+	.getc = htif_serial_getc,
+	.pending = htif_serial_pending,
+};
+
+static const struct udevice_id htif_serial_ids[] = {
+	{ .compatible = "ucb,htif0" },
+	{ }
+};
+
+U_BOOT_DRIVER(serial_htif) = {
+	.name		= "serial_htif",
+	.id		= UCLASS_SERIAL,
+	.of_match	= htif_serial_ids,
+	.of_to_plat	= htif_serial_of_to_plat,
+	.plat_auto	= sizeof(struct htif_plat),
+	.probe		= htif_serial_probe,
+	.ops		= &htif_serial_ops,
+};