drivers: serial: Add SiFive UART driver

This patch adds SiFive UART driver. The driver is 100% DM driver
and it determines input clock using clk framework.

Signed-off-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

drivers/serial/Kconfig

@@ -343,6 +343,13 @@ config DEBUG_UART_SANDBOX
 	  start up driver model. The driver will be available until the real
 	  driver model serial is running.
 
+config DEBUG_UART_SIFIVE
+	bool "SiFive UART"
+	help
+	  Select this to enable a debug UART using the serial_sifive driver. You
+	  will need to provide parameters to make this work. The driver will
+	  be available until the real driver-model serial is running.
+
 config DEBUG_UART_STM32
 	bool "STMicroelectronics STM32"
 	depends on STM32_SERIAL
@@ -679,6 +686,12 @@ 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 SIFIVE_SERIAL
+	bool "SiFive UART support"
+	depends on DM_SERIAL
+	help
+	  This driver supports the SiFive UART. If unsure say N.
+
 config STI_ASC_SERIAL
 	bool "STMicroelectronics on-chip UART"
 	depends on DM_SERIAL && ARCH_STI

drivers/serial/Makefile

@@ -67,6 +67,7 @@ obj-$(CONFIG_NULLDEV_SERIAL) += serial_nulldev.o
 obj-$(CONFIG_OWL_SERIAL) += serial_owl.o
 obj-$(CONFIG_OMAP_SERIAL) += serial_omap.o
 obj-$(CONFIG_MTK_SERIAL) += serial_mtk.o
+obj-$(CONFIG_SIFIVE_SERIAL) += serial_sifive.o
 
 ifndef CONFIG_SPL_BUILD
 obj-$(CONFIG_USB_TTY) += usbtty.o

drivers/serial/serial_sifive.c

@@ -0,0 +1,215 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2018 Anup Patel <anup@brainfault.org>
+ */
+
+#include <clk.h>
+#include <common.h>
+#include <debug_uart.h>
+#include <dm.h>
+#include <errno.h>
+#include <fdtdec.h>
+#include <watchdog.h>
+#include <asm/io.h>
+#include <linux/compiler.h>
+#include <serial.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+#define UART_TXFIFO_FULL	0x80000000
+#define UART_RXFIFO_EMPTY	0x80000000
+#define UART_RXFIFO_DATA	0x000000ff
+#define UART_TXCTRL_TXEN	0x1
+#define UART_RXCTRL_RXEN	0x1
+
+struct uart_sifive {
+	u32 txfifo;
+	u32 rxfifo;
+	u32 txctrl;
+	u32 rxctrl;
+	u32 ie;
+	u32 ip;
+	u32 div;
+};
+
+struct sifive_uart_platdata {
+	unsigned int clock;
+	int saved_input_char;
+	struct uart_sifive *regs;
+};
+
+/* Set up the baud rate in gd struct */
+static void _sifive_serial_setbrg(struct uart_sifive *regs,
+				  unsigned long clock, unsigned long baud)
+{
+	writel((u32)((clock / baud) - 1), &regs->div);
+}
+
+static void _sifive_serial_init(struct uart_sifive *regs)
+{
+	writel(UART_TXCTRL_TXEN, &regs->txctrl);
+	writel(UART_RXCTRL_RXEN, &regs->rxctrl);
+	writel(0, &regs->ie);
+}
+
+static int _sifive_serial_putc(struct uart_sifive *regs, const char c)
+{
+	if (readl(&regs->txfifo) & UART_TXFIFO_FULL)
+		return -EAGAIN;
+
+	writel(c, &regs->txfifo);
+
+	return 0;
+}
+
+static int _sifive_serial_getc(struct uart_sifive *regs)
+{
+	int ch = readl(&regs->rxfifo);
+
+	if (ch & UART_RXFIFO_EMPTY)
+		return -EAGAIN;
+	ch &= UART_RXFIFO_DATA;
+
+	return (!ch) ? -EAGAIN : ch;
+}
+
+static int sifive_serial_setbrg(struct udevice *dev, int baudrate)
+{
+	int err;
+	struct clk clk;
+	struct sifive_uart_platdata *platdata = dev_get_platdata(dev);
+
+	err = clk_get_by_index(dev, 0, &clk);
+	if (!err) {
+		err = clk_get_rate(&clk);
+		if (!IS_ERR_VALUE(err))
+			platdata->clock = err;
+	} else if (err != -ENOENT && err != -ENODEV && err != -ENOSYS) {
+		debug("SiFive UART failed to get clock\n");
+		return err;
+	}
+
+	if (!platdata->clock)
+		platdata->clock = dev_read_u32_default(dev, "clock-frequency", 0);
+	if (!platdata->clock) {
+		debug("SiFive UART clock not defined\n");
+		return -EINVAL;
+	}
+
+	_sifive_serial_setbrg(platdata->regs, platdata->clock, baudrate);
+
+	return 0;
+}
+
+static int sifive_serial_probe(struct udevice *dev)
+{
+	struct sifive_uart_platdata *platdata = dev_get_platdata(dev);
+
+	/* No need to reinitialize the UART after relocation */
+	if (gd->flags & GD_FLG_RELOC)
+		return 0;
+
+	platdata->saved_input_char = 0;
+	_sifive_serial_init(platdata->regs);
+
+	return 0;
+}
+
+static int sifive_serial_getc(struct udevice *dev)
+{
+	int c;
+	struct sifive_uart_platdata *platdata = dev_get_platdata(dev);
+	struct uart_sifive *regs = platdata->regs;
+
+	if (platdata->saved_input_char > 0) {
+		c = platdata->saved_input_char;
+		platdata->saved_input_char = 0;
+		return c;
+	}
+
+	while ((c = _sifive_serial_getc(regs)) == -EAGAIN) ;
+
+	return c;
+}
+
+static int sifive_serial_putc(struct udevice *dev, const char ch)
+{
+	int rc;
+	struct sifive_uart_platdata *platdata = dev_get_platdata(dev);
+
+	while ((rc = _sifive_serial_putc(platdata->regs, ch)) == -EAGAIN) ;
+
+	return rc;
+}
+
+static int sifive_serial_pending(struct udevice *dev, bool input)
+{
+	struct sifive_uart_platdata *platdata = dev_get_platdata(dev);
+	struct uart_sifive *regs = platdata->regs;
+
+	if (input) {
+		if (platdata->saved_input_char > 0)
+			return 1;
+		platdata->saved_input_char = _sifive_serial_getc(regs);
+		return (platdata->saved_input_char > 0) ? 1 : 0;
+	} else {
+		return !!(readl(&regs->txfifo) & UART_TXFIFO_FULL);
+	}
+}
+
+static int sifive_serial_ofdata_to_platdata(struct udevice *dev)
+{
+	struct sifive_uart_platdata *platdata = dev_get_platdata(dev);
+
+	platdata->regs = (struct uart_sifive *)dev_read_addr(dev);
+	if (IS_ERR(platdata->regs))
+		return PTR_ERR(platdata->regs);
+
+	return 0;
+}
+
+static const struct dm_serial_ops sifive_serial_ops = {
+	.putc = sifive_serial_putc,
+	.getc = sifive_serial_getc,
+	.pending = sifive_serial_pending,
+	.setbrg = sifive_serial_setbrg,
+};
+
+static const struct udevice_id sifive_serial_ids[] = {
+	{ .compatible = "sifive,uart0" },
+	{ }
+};
+
+U_BOOT_DRIVER(serial_sifive) = {
+	.name	= "serial_sifive",
+	.id	= UCLASS_SERIAL,
+	.of_match = sifive_serial_ids,
+	.ofdata_to_platdata = sifive_serial_ofdata_to_platdata,
+	.platdata_auto_alloc_size = sizeof(struct sifive_uart_platdata),
+	.probe = sifive_serial_probe,
+	.ops	= &sifive_serial_ops,
+};
+
+#ifdef CONFIG_DEBUG_UART_SIFIVE
+static inline void _debug_uart_init(void)
+{
+	struct uart_sifive *regs =
+			(struct uart_sifive *)CONFIG_DEBUG_UART_BASE;
+
+	_sifive_serial_setbrg(regs, CONFIG_DEBUG_UART_CLOCK,
+			      CONFIG_BAUDRATE);
+	_sifive_serial_init(regs);
+}
+
+static inline void _debug_uart_putc(int ch)
+{
+	struct uart_sifive *regs =
+			(struct uart_sifive *)CONFIG_DEBUG_UART_BASE;
+
+	while (_sifive_serial_putc(regs, ch) == -EAGAIN)
+		WATCHDOG_RESET();
+}
+
+DEBUG_UART_FUNCS
+
+#endif