[PATCH v3 0/2] tty: serial: add DT bindings and serial driver for the SiFive FU540 UART

[PATCH v3 0/2] tty: serial: add DT bindings and serial driver for the SiFive FU540 UART

[Paul Walmsley]

This series adds a serial driver, with console support, for the
UART IP block present on the SiFive FU540 SoC.  The programming
model is straightforward, but unique.

Boot-tested on a SiFive FU540 HiFive-U board (with appropriate patches
to the DT data).

The patches in this series can also be found at:

https://github.com/sifive/riscv-linux/tree/dev/paulw/serial-v4.19-rc7

This third version updates the DT binding documentation per discussion
with Rob Herring and fixes one additional issue identified by the 0-day
build system related to MODULE_DEVICE_TABLE.

Paul Walmsley (2):
  dt-bindings: serial: add documentation for the SiFive UART driver
  tty: serial: add driver for the SiFive UART

 .../bindings/serial/sifive-serial.txt         |   33 +
 drivers/tty/serial/Kconfig                    |   24 +
 drivers/tty/serial/Makefile                   |    1 +
 drivers/tty/serial/sifive.c                   | 1067 +++++++++++++++++
 include/uapi/linux/serial_core.h              |    3 +
 5 files changed, 1128 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/serial/sifive-serial.txt
 create mode 100644 drivers/tty/serial/sifive.c


Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Wesley Terpstra <wesley@sifive.com>
Cc: linux-serial at vger.kernel.org
Cc: linux-riscv at lists.infradead.org
Cc: linux-kernel at vger.kernel.org
Cc: devicetree at vger.kernel.org

-- 
2.19.1

[PATCH v3 0/2] tty: serial: add DT bindings and serial driver for the SiFive FU540 UART

[Paul Walmsley]

This series adds a serial driver, with console support, for the
UART IP block present on the SiFive FU540 SoC.  The programming
model is straightforward, but unique.

Boot-tested on a SiFive FU540 HiFive-U board (with appropriate patches
to the DT data).

The patches in this series can also be found at:

https://github.com/sifive/riscv-linux/tree/dev/paulw/serial-v4.19-rc7

This third version updates the DT binding documentation per discussion
with Rob Herring and fixes one additional issue identified by the 0-day
build system related to MODULE_DEVICE_TABLE.

Paul Walmsley (2):
  dt-bindings: serial: add documentation for the SiFive UART driver
  tty: serial: add driver for the SiFive UART

 .../bindings/serial/sifive-serial.txt         |   33 +
 drivers/tty/serial/Kconfig                    |   24 +
 drivers/tty/serial/Makefile                   |    1 +
 drivers/tty/serial/sifive.c                   | 1067 +++++++++++++++++
 include/uapi/linux/serial_core.h              |    3 +
 5 files changed, 1128 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/serial/sifive-serial.txt
 create mode 100644 drivers/tty/serial/sifive.c


Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Wesley Terpstra <wesley@sifive.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-riscv@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org

-- 
2.19.1


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[PATCH v3 1/2] dt-bindings: serial: add documentation for the SiFive UART driver

[Paul Walmsley]

Add DT binding documentation for the Linux driver for the SiFive
asynchronous serial IP block.

Cc: linux-serial at vger.kernel.org
Cc: devicetree at vger.kernel.org
Cc: linux-riscv at lists.infradead.org
Cc: linux-kernel at vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
---
v3: update description and example for compatible strings, per
    discussion with Rob Herring.

 .../bindings/serial/sifive-serial.txt         | 33 +++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/serial/sifive-serial.txt

diff --git a/Documentation/devicetree/bindings/serial/sifive-serial.txt b/Documentation/devicetree/bindings/serial/sifive-serial.txt
new file mode 100644
index 000000000000..a426b18ba049
--- /dev/null
+++ b/Documentation/devicetree/bindings/serial/sifive-serial.txt
@@ -0,0 +1,33 @@
+SiFive asynchronous serial interface (UART)
+
+Required properties:
+
+- compatible: should be something similar to
+	      "sifive,<chip>-uart<version>" for the UART as integrated
+	      on a particular chip, and "sifive,uart<version>" for the
+	      general UART IP block programming model.	Supported
+	      compatible strings as of the date of this writing are:
+	      "sifive,fu540-c000-uart0" for the SiFive UART v0 as
+	      integrated onto the SiFive FU540 chip, or "sifive,uart0"
+	      for the SiFive UART v0 IP block with no chip integration
+	      tweaks (if any)
+- reg: address and length of the register space
+- interrupts: Should contain the UART interrupt identifier
+- clocks: Should contain a clock identifier for the UART's parent clock
+
+
+UART RTL that corresponds to the IP block version numbers can be found
+here:
+
+https://github.com/sifive/sifive-blocks/tree/master/src/main/scala/devices/uart
+
+
+Example:
+
+uart0: serial at 10010000 {
+	compatible = "sifive,fu540-c000-uart0", "sifive,uart0";
+	interrupt-parent = <&plic0>;
+	interrupts = <80>;
+	reg = <0x0 0x10010000 0x0 0x1000>;
+	clocks = <&prci PRCI_CLK_TLCLK>;
+};
-- 
2.19.1

[PATCH v3 1/2] dt-bindings: serial: add documentation for the SiFive UART driver

[Paul Walmsley]

Add DT binding documentation for the Linux driver for the SiFive
asynchronous serial IP block.

Cc: linux-serial@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-riscv@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
---
v3: update description and example for compatible strings, per
    discussion with Rob Herring.

 .../bindings/serial/sifive-serial.txt         | 33 +++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/serial/sifive-serial.txt

diff --git a/Documentation/devicetree/bindings/serial/sifive-serial.txt b/Documentation/devicetree/bindings/serial/sifive-serial.txt
new file mode 100644
index 000000000000..a426b18ba049
--- /dev/null
+++ b/Documentation/devicetree/bindings/serial/sifive-serial.txt
@@ -0,0 +1,33 @@
+SiFive asynchronous serial interface (UART)
+
+Required properties:
+
+- compatible: should be something similar to
+	      "sifive,<chip>-uart<version>" for the UART as integrated
+	      on a particular chip, and "sifive,uart<version>" for the
+	      general UART IP block programming model.	Supported
+	      compatible strings as of the date of this writing are:
+	      "sifive,fu540-c000-uart0" for the SiFive UART v0 as
+	      integrated onto the SiFive FU540 chip, or "sifive,uart0"
+	      for the SiFive UART v0 IP block with no chip integration
+	      tweaks (if any)
+- reg: address and length of the register space
+- interrupts: Should contain the UART interrupt identifier
+- clocks: Should contain a clock identifier for the UART's parent clock
+
+
+UART RTL that corresponds to the IP block version numbers can be found
+here:
+
+https://github.com/sifive/sifive-blocks/tree/master/src/main/scala/devices/uart
+
+
+Example:
+
+uart0: serial@10010000 {
+	compatible = "sifive,fu540-c000-uart0", "sifive,uart0";
+	interrupt-parent = <&plic0>;
+	interrupts = <80>;
+	reg = <0x0 0x10010000 0x0 0x1000>;
+	clocks = <&prci PRCI_CLK_TLCLK>;
+};
-- 
2.19.1


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[PATCH v3 2/2] tty: serial: add driver for the SiFive UART

[Paul Walmsley]

Add a serial driver for the SiFive UART, found on SiFive FU540 devices
(among others).

The underlying serial IP block is relatively basic, and currently does
not support serial break detection.  Further information on the IP
block can be found in the documentation and Chisel sources:

https://static.dev.sifive.com/FU540-C000-v1.0.pdf

https://github.com/sifive/sifive-blocks/tree/master/src/main/scala/devices/uart

This driver was written in collaboration with Wesley Terpstra
<wesley@sifive.com>.

Boot-tested on a SiFive HiFive Unleashed A00 board.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Wesley Terpstra <wesley@sifive.com>
Cc: linux-serial at vger.kernel.org
Cc: linux-riscv at lists.infradead.org
Cc: linux-kernel at vger.kernel.org
Cc: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
---
v3: fix MODULE_DEVICE_TABLE argument
v2: remove leftover junk related to CONFIG_CONSOLE_POLL; add missing
    spin_unlock() in ISR found by 0-day and Julia Lawall

 drivers/tty/serial/Kconfig       |   24 +
 drivers/tty/serial/Makefile      |    1 +
 drivers/tty/serial/sifive.c      | 1067 ++++++++++++++++++++++++++++++
 include/uapi/linux/serial_core.h |    3 +
 4 files changed, 1095 insertions(+)
 create mode 100644 drivers/tty/serial/sifive.c

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index df8bd0c7b97d..fdd624df75c8 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1060,6 +1060,30 @@ config SERIAL_OMAP_CONSOLE
 	  your boot loader about how to pass options to the kernel at
 	  boot time.)
 
+config SERIAL_SIFIVE
+	tristate "SiFive UART support"
+	depends on OF
+	select SERIAL_CORE
+	help
+	  Select this option if you are building a kernel for a device that
+	  contains a SiFive UART IP block.  This type of UART is present on
+	  SiFive FU540 SoCs, among others.
+
+config SERIAL_SIFIVE_CONSOLE
+	bool "Console on SiFive UART"
+	depends on SERIAL_SIFIVE=y
+	select SERIAL_CORE_CONSOLE
+	help
+	  Select this option if you would like to use a SiFive UART as the
+	  system console.
+
+	  Even if you say Y here, the currently visible virtual console
+	  (/dev/tty0) will still be used as the system console by default, but
+	  you can alter that using a kernel command line option such as
+	  "console=ttySIFx". (Try "man bootparam" or see the documentation of
+	  your boot loader about how to pass options to the kernel at
+	  boot time.)
+
 config SERIAL_LANTIQ
 	bool "Lantiq serial driver"
 	depends on LANTIQ
diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index daac675612df..7e906d3c0455 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile
@@ -89,6 +89,7 @@ obj-$(CONFIG_SERIAL_MVEBU_UART)	+= mvebu-uart.o
 obj-$(CONFIG_SERIAL_PIC32)	+= pic32_uart.o
 obj-$(CONFIG_SERIAL_MPS2_UART)	+= mps2-uart.o
 obj-$(CONFIG_SERIAL_OWL)	+= owl-uart.o
+obj-$(CONFIG_SERIAL_SIFIVE)	+= sifive.o
 
 # GPIOLIB helpers for modem control lines
 obj-$(CONFIG_SERIAL_MCTRL_GPIO)	+= serial_mctrl_gpio.o
diff --git a/drivers/tty/serial/sifive.c b/drivers/tty/serial/sifive.c
new file mode 100644
index 000000000000..80c06039fb57
--- /dev/null
+++ b/drivers/tty/serial/sifive.c
@@ -0,0 +1,1067 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * SiFive UART driver
+ * Copyright (C) 2018 Paul Walmsley <paul@pwsan.com>
+ * Copyright (C) 2018 SiFive
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * Based partially on:
+ * - drivers/tty/serial/pxa.c
+ * - drivers/tty/serial/amba-pl011.c
+ * - drivers/tty/serial/uartlite.c
+ * - drivers/tty/serial/omap-serial.c
+ * - drivers/pwm/pwm-sifive.c
+ *
+ * See the following sources for further documentation:
+ * - Chapter 19 "Universal Asynchronous Receiver/Transmitter (UART)" of
+ *   SiFive FE310-G000 v2p3
+ * - The tree/master/src/main/scala/devices/uart directory of
+ *   https://github.com/sifive/sifive-blocks/
+ *
+ * The SiFive UART design is not 8250-compatible.  The following common
+ * features are not supported:
+ * - Word lengths other than 8 bits
+ * - Break handling
+ * - Parity
+ * - Flow control
+ * - Modem signals (DSR, RI, etc.)
+ * On the other hand, the design is free from the baggage of the 8250
+ * programming model.
+ */
+
+#include <linux/clk.h>
+#include <linux/console.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/irq.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/platform_device.h>
+#include <linux/serial_core.h>
+#include <linux/serial_reg.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+
+/*
+ * Register offsets
+ */
+
+/* TXDATA */
+#define SIFIVE_SERIAL_TXDATA_OFFS		0x0
+#define SIFIVE_SERIAL_TXDATA_FULL_SHIFT		31
+#define SIFIVE_SERIAL_TXDATA_FULL_MASK		(1 << SIFIVE_SERIAL_TXDATA_FULL_SHIFT)
+#define SIFIVE_SERIAL_TXDATA_DATA_SHIFT		0
+#define SIFIVE_SERIAL_TXDATA_DATA_MASK		(0xff << SIFIVE_SERIAL_TXDATA_DATA_SHIFT)
+
+/* RXDATA */
+#define SIFIVE_SERIAL_RXDATA_OFFS		0x4
+#define SIFIVE_SERIAL_RXDATA_EMPTY_SHIFT	31
+#define SIFIVE_SERIAL_RXDATA_EMPTY_MASK		(1 << SIFIVE_SERIAL_RXDATA_EMPTY_SHIFT)
+#define SIFIVE_SERIAL_RXDATA_DATA_SHIFT		0
+#define SIFIVE_SERIAL_RXDATA_DATA_MASK		(0xff << SIFIVE_SERIAL_RXDATA_DATA_SHIFT)
+
+/* TXCTRL */
+#define SIFIVE_SERIAL_TXCTRL_OFFS		0x8
+#define SIFIVE_SERIAL_TXCTRL_TXCNT_SHIFT	16
+#define SIFIVE_SERIAL_TXCTRL_TXCNT_MASK		(0x7 << SIFIVE_SERIAL_TXCTRL_TXCNT_SHIFT)
+#define SIFIVE_SERIAL_TXCTRL_NSTOP_SHIFT	1
+#define SIFIVE_SERIAL_TXCTRL_NSTOP_MASK		(1 << SIFIVE_SERIAL_TXCTRL_NSTOP_SHIFT)
+#define SIFIVE_SERIAL_TXCTRL_TXEN_SHIFT		0
+#define SIFIVE_SERIAL_TXCTRL_TXEN_MASK		(1 << SIFIVE_SERIAL_TXCTRL_TXEN_SHIFT)
+
+/* RXCTRL */
+#define SIFIVE_SERIAL_RXCTRL_OFFS		0xC
+#define SIFIVE_SERIAL_RXCTRL_RXCNT_SHIFT	16
+#define SIFIVE_SERIAL_RXCTRL_RXCNT_MASK		(0x7 << SIFIVE_SERIAL_TXCTRL_TXCNT_SHIFT)
+#define SIFIVE_SERIAL_RXCTRL_RXEN_SHIFT		0
+#define SIFIVE_SERIAL_RXCTRL_RXEN_MASK		(1 << SIFIVE_SERIAL_RXCTRL_RXEN_SHIFT)
+
+/* IE */
+#define SIFIVE_SERIAL_IE_OFFS			0x10
+#define SIFIVE_SERIAL_IE_RXWM_SHIFT		1
+#define SIFIVE_SERIAL_IE_RXWM_MASK		(1 << SIFIVE_SERIAL_IE_RXWM_SHIFT)
+#define SIFIVE_SERIAL_IE_TXWM_SHIFT		0
+#define SIFIVE_SERIAL_IE_TXWM_MASK		(1 << SIFIVE_SERIAL_IE_TXWM_SHIFT)
+
+/* IP */
+#define SIFIVE_SERIAL_IP_OFFS			0x14
+#define SIFIVE_SERIAL_IP_RXWM_SHIFT		1
+#define SIFIVE_SERIAL_IP_RXWM_MASK		(1 << SIFIVE_SERIAL_IP_RXWM_SHIFT)
+#define SIFIVE_SERIAL_IP_TXWM_SHIFT		0
+#define SIFIVE_SERIAL_IP_TXWM_MASK		(1 << SIFIVE_SERIAL_IP_TXWM_SHIFT)
+
+/* DIV */
+#define SIFIVE_SERIAL_DIV_OFFS			0x18
+#define SIFIVE_SERIAL_DIV_DIV_SHIFT		0
+#define SIFIVE_SERIAL_DIV_DIV_MASK		(0xffff << SIFIVE_SERIAL_IP_DIV_SHIFT)
+
+/*
+ * Config macros
+ */
+
+/*
+ * SIFIVE_SERIAL_MAX_PORTS: maximum number of UARTs on a device that can
+ *                          host a serial console
+ */
+#define SIFIVE_SERIAL_MAX_PORTS			8
+
+/*
+ * SIFIVE_DEFAULT_BAUD_RATE: default baud rate that the driver should
+ *                           configure itself to use
+ */
+#define SIFIVE_DEFAULT_BAUD_RATE		115200
+
+/* SIFIVE_SERIAL_NAME: our driver's name that we pass to the operating system */
+#define SIFIVE_SERIAL_NAME			"sifive-serial"
+
+/* SIFIVE_TTY_PREFIX: tty name prefix for SiFive serial ports */
+#define SIFIVE_TTY_PREFIX			"ttySIF"
+
+/* SIFIVE_TX_FIFO_DEPTH: depth of the TX FIFO (in bytes) */
+#define SIFIVE_TX_FIFO_DEPTH			8
+
+/* SIFIVE_RX_FIFO_DEPTH: depth of the TX FIFO (in bytes) */
+#define SIFIVE_RX_FIFO_DEPTH			8
+
+#if (SIFIVE_TX_FIFO_DEPTH != SIFIVE_RX_FIFO_DEPTH)
+#error Driver does not support configurations with different TX, RX FIFO sizes
+#endif
+
+/*
+ *
+ */
+
+/**
+ * sifive_serial_port - driver-specific data extension to struct uart_port
+ * @port: struct uart_port embedded in this struct
+ * @dev: struct device *
+ * @ier: shadowed copy of the interrupt enable register
+ * @clkin_rate: input clock to the UART IP block.
+ * @baud_rate: UART serial line rate (e.g., 115200 baud)
+ * @clk_notifier: clock rate change notifier for upstream clock changes
+ *
+ * Configuration data specific to this SiFive UART.
+ */
+struct sifive_serial_port {
+	struct uart_port	port;
+	struct device		*dev;
+	unsigned char		ier;
+	unsigned long		clkin_rate;
+	unsigned long		baud_rate;
+	struct clk		*clk;
+	struct notifier_block	clk_notifier;
+};
+
+/*
+ * Structure container-of macros
+ */
+
+#define port_to_sifive_serial_port(p) (container_of((p), \
+						    struct sifive_serial_port, \
+						    port))
+
+#define notifier_to_sifive_serial_port(nb) (container_of((nb), \
+							 struct sifive_serial_port, \
+							 clk_notifier))
+
+/*
+ * Forward declarations
+ */
+static void sifive_serial_stop_tx(struct uart_port *port);
+
+/*
+ * Internal functions
+ */
+
+/**
+ * __ssp_early_writel() - write to a SiFive serial port register (early)
+ * @port: pointer to a struct uart_port record
+ * @offs: register address offset from the IP block base address
+ * @v: value to write to the register
+ *
+ * Given a pointer @port to a struct uart_port record, write the value
+ * @v to the IP block register address offset @offs.  This function is
+ * intended for early console use.
+ *
+ * Context: Intended to be used only by the earlyconsole code.
+ */
+static void __ssp_early_writel(u32 v, u16 offs, struct uart_port *port)
+{
+	writel_relaxed(v, port->membase + offs);
+}
+
+/**
+ * __ssp_early_readl() - read from a SiFive serial port register (early)
+ * @port: pointer to a struct uart_port record
+ * @offs: register address offset from the IP block base address
+ *
+ * Given a pointer @port to a struct uart_port record, read the
+ * contents of the IP block register located at offset @offs from the
+ * IP block base and return it.  This function is intended for early
+ * console use.
+ *
+ * Context: Intended to be called only by the earlyconsole code or by
+ *          __ssp_readl() or __ssp_writel() (in this driver)
+ *
+ * Returns: the register value read from the UART.
+ */
+static u32 __ssp_early_readl(struct uart_port *port, u16 offs)
+{
+	return readl_relaxed(port->membase + offs);
+}
+
+/**
+ * __ssp_writel() - write to a SiFive serial port register
+ * @v: value to write to the register
+ * @offs: register address offset from the IP block base address
+ * @ssp: pointer to a struct sifive_serial_port record
+ *
+ * Write the value @v to the IP block register located at offset @offs from the
+ * IP block base, given a pointer @ssp to a struct sifive_serial_port record.
+ *
+ * Context: Any context.
+ */
+static void __ssp_writel(u32 v, u16 offs, struct sifive_serial_port *ssp)
+{
+	__ssp_early_writel(v, offs, &ssp->port);
+}
+
+/**
+ * __ssp_readl() - read from a SiFive serial port register
+ * @ssp: pointer to a struct sifive_serial_port record
+ * @offs: register address offset from the IP block base address
+ *
+ * Read the contents of the IP block register located at offset @offs from the
+ * IP block base, given a pointer @ssp to a struct sifive_serial_port record.
+ *
+ * Context: Any context.
+ *
+ * Returns: the value of the UART register
+ */
+static u32 __ssp_readl(struct sifive_serial_port *ssp, u16 offs)
+{
+	return __ssp_early_readl(&ssp->port, offs);
+}
+
+/**
+ * sifive_serial_is_txfifo_full() - is the TXFIFO full?
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Read the transmit FIFO "full" bit, returning a non-zero value if the
+ * TX FIFO is full, or zero if space remains.  Intended to be used to prevent
+ * writes to the TX FIFO when it's full.
+ *
+ * Returns: SIFIVE_SERIAL_TXDATA_FULL_MASK (non-zero) if the transmit FIFO
+ * is full, or 0 if space remains.
+ */
+static int sifive_serial_is_txfifo_full(struct sifive_serial_port *ssp)
+{
+	return __ssp_readl(ssp, SIFIVE_SERIAL_TXDATA_OFFS) &
+		SIFIVE_SERIAL_TXDATA_FULL_MASK;
+}
+
+/**
+ * __ssp_transmit_char() - enqueue a byte to transmit onto the TX FIFO
+ * @ssp: pointer to a struct sifive_serial_port
+ * @ch: character to transmit
+ *
+ * Enqueue a byte @ch onto the transmit FIFO, given a pointer @ssp to the
+ * struct sifive_serial_port * to transmit on.  Caller should first check to
+ * ensure that the TXFIFO has space; see sifive_serial_is_txfifo_full().
+ *
+ * Context: Any context.
+ */
+static void __ssp_transmit_char(struct sifive_serial_port *ssp, int ch)
+{
+	__ssp_writel(ch, SIFIVE_SERIAL_TXDATA_OFFS, ssp);
+}
+
+/**
+ * __ssp_transmit_chars() - enqueue multiple bytes onto the TX FIFO
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Transfer up to a TX FIFO size's worth of characters from the Linux serial
+ * transmit buffer to the SiFive UART TX FIFO.
+ *
+ * Context: Any context.  Expects @ssp->port.lock to be held by caller.
+ */
+static void __ssp_transmit_chars(struct sifive_serial_port *ssp)
+{
+	struct circ_buf *xmit = &ssp->port.state->xmit;
+	int count;
+
+	if (ssp->port.x_char) {
+		__ssp_transmit_char(ssp, ssp->port.x_char);
+		ssp->port.icount.tx++;
+		ssp->port.x_char = 0;
+		return;
+	}
+	if (uart_circ_empty(xmit) || uart_tx_stopped(&ssp->port)) {
+		sifive_serial_stop_tx(&ssp->port);
+		return;
+	}
+	count = SIFIVE_TX_FIFO_DEPTH;
+	do {
+		__ssp_transmit_char(ssp, xmit->buf[xmit->tail]);
+		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+		ssp->port.icount.tx++;
+		if (uart_circ_empty(xmit))
+			break;
+	} while (--count > 0);
+
+	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+		uart_write_wakeup(&ssp->port);
+
+	if (uart_circ_empty(xmit))
+		sifive_serial_stop_tx(&ssp->port);
+}
+
+/**
+ * __ssp_enable_txwm() - enable transmit watermark interrupts
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Enable interrupt generation when the transmit FIFO watermark is reached
+ * on the SiFive UART referred to by @ssp.
+ */
+static void __ssp_enable_txwm(struct sifive_serial_port *ssp)
+{
+	if (ssp->ier & SIFIVE_SERIAL_IE_TXWM_MASK)
+		return;
+
+	ssp->ier |= SIFIVE_SERIAL_IE_TXWM_MASK;
+	__ssp_writel(ssp->ier, SIFIVE_SERIAL_IE_OFFS, ssp);
+}
+
+/**
+ * __ssp_enable_rxwm() - enable receive watermark interrupts
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Enable interrupt generation when the receive FIFO watermark is reached
+ * on the SiFive UART referred to by @ssp.
+ */
+static void __ssp_enable_rxwm(struct sifive_serial_port *ssp)
+{
+	if (ssp->ier & SIFIVE_SERIAL_IE_RXWM_MASK)
+		return;
+
+	ssp->ier |= SIFIVE_SERIAL_IE_RXWM_MASK;
+	__ssp_writel(ssp->ier, SIFIVE_SERIAL_IE_OFFS, ssp);
+}
+
+/**
+ * __ssp_disable_txwm() - disable transmit watermark interrupts
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Disable interrupt generation when the transmit FIFO watermark is reached
+ * on the UART referred to by @ssp.
+ */
+static void __ssp_disable_txwm(struct sifive_serial_port *ssp)
+{
+	if (!(ssp->ier & SIFIVE_SERIAL_IE_TXWM_MASK))
+		return;
+
+	ssp->ier &= ~SIFIVE_SERIAL_IE_TXWM_MASK;
+	__ssp_writel(ssp->ier, SIFIVE_SERIAL_IE_OFFS, ssp);
+}
+
+/**
+ * __ssp_disable_rxwm() - disable receive watermark interrupts
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Disable interrupt generation when the receive FIFO watermark is reached
+ * on the UART referred to by @ssp.
+ */
+static void __ssp_disable_rxwm(struct sifive_serial_port *ssp)
+{
+	if (!(ssp->ier & SIFIVE_SERIAL_IE_RXWM_MASK))
+		return;
+
+	ssp->ier &= ~SIFIVE_SERIAL_IE_RXWM_MASK;
+	__ssp_writel(ssp->ier, SIFIVE_SERIAL_IE_OFFS, ssp);
+}
+
+/**
+ * __ssp_receive_char() - receive a byte from the UART
+ * @ssp: pointer to a struct sifive_serial_port
+ * @is_empty: char pointer to return whether the RX FIFO is empty
+ *
+ * Try to read a byte from the SiFive UART RX FIFO, referenced by
+ * @ssp, and to return it.  Also returns the RX FIFO empty bit in
+ * the char pointed to by @ch.  The caller must pass the byte back to the
+ * Linux serial layer if needed.
+ *
+ * Returns: the byte read from the UART RX FIFO.
+ */
+static char __ssp_receive_char(struct sifive_serial_port *ssp, char *is_empty)
+{
+	u32 v;
+	u8 ch;
+
+	v = __ssp_readl(ssp, SIFIVE_SERIAL_RXDATA_OFFS);
+
+	if (!is_empty)
+		WARN_ON(1);
+	else
+		*is_empty = (v & SIFIVE_SERIAL_RXDATA_EMPTY_MASK) >>
+			SIFIVE_SERIAL_RXDATA_EMPTY_SHIFT;
+
+	ch = (v & SIFIVE_SERIAL_RXDATA_DATA_MASK) >>
+		SIFIVE_SERIAL_RXDATA_DATA_SHIFT;
+
+	return ch;
+}
+
+/**
+ * __ssp_receive_chars() - receive multiple bytes from the UART
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Receive up to an RX FIFO's worth of bytes from the SiFive UART referred
+ * to by @ssp and pass them up to the Linux serial layer.
+ *
+ * Context: Expects ssp->port.lock to be held by caller.
+ */
+static void __ssp_receive_chars(struct sifive_serial_port *ssp)
+{
+	unsigned char ch;
+	char is_empty;
+	int c;
+
+	for (c = SIFIVE_RX_FIFO_DEPTH; c > 0; --c) {
+		ch = __ssp_receive_char(ssp, &is_empty);
+		if (is_empty)
+			break;
+
+		ssp->port.icount.rx++;
+		uart_insert_char(&ssp->port, 0, 0, ch, TTY_NORMAL);
+	}
+
+	spin_unlock(&ssp->port.lock);
+	tty_flip_buffer_push(&ssp->port.state->port);
+	spin_lock(&ssp->port.lock);
+}
+
+/**
+ * __ssp_update_div() - calculate the divisor setting by the line rate
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Calculate the appropriate value of the clock divisor for the UART
+ * and target line rate referred to by @ssp and write it into the
+ * hardware.
+ */
+static void __ssp_update_div(struct sifive_serial_port *ssp)
+{
+	u16 div;
+
+	div = DIV_ROUND_UP(ssp->clkin_rate, ssp->baud_rate) - 1;
+
+	__ssp_writel(div, SIFIVE_SERIAL_DIV_OFFS, ssp);
+}
+
+/**
+ * __ssp_update_baud_rate() - set the UART "baud rate"
+ * @ssp: pointer to a struct sifive_serial_port
+ * @rate: new target bit rate
+ *
+ * Calculate the UART divisor value for the target bit rate @rate for the
+ * SiFive UART described by @ssp and program it into the UART.  There may
+ * be some error between the target bit rate and the actual bit rate implemented
+ * by the UART due to clock ratio granularity.
+ */
+static void __ssp_update_baud_rate(struct sifive_serial_port *ssp,
+				   unsigned int rate)
+{
+	if (ssp->baud_rate == rate)
+		return;
+
+	ssp->baud_rate = rate;
+	__ssp_update_div(ssp);
+}
+
+/**
+ * __ssp_set_stop_bits() - set the number of stop bits
+ * @ssp: pointer to a struct sifive_serial_port
+ * @nstop: 1 or 2 (stop bits)
+ *
+ * Program the SiFive UART referred to by @ssp to use @nstop stop bits.
+ */
+static void __ssp_set_stop_bits(struct sifive_serial_port *ssp, char nstop)
+{
+	u32 v;
+
+	if (nstop < 1 || nstop > 2) {
+		WARN_ON(1);
+		return;
+	}
+
+	v = __ssp_readl(ssp, SIFIVE_SERIAL_TXCTRL_OFFS);
+	v &= ~SIFIVE_SERIAL_TXCTRL_NSTOP_MASK;
+	v |= (nstop - 1) << SIFIVE_SERIAL_TXCTRL_NSTOP_SHIFT;
+	__ssp_writel(v, SIFIVE_SERIAL_TXCTRL_OFFS, ssp);
+}
+
+/**
+ * __ssp_wait_for_xmitr() - wait for an empty slot on the TX FIFO
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Delay while the UART TX FIFO referred to by @ssp is marked as full.
+ *
+ * Context: Any context.
+ */
+static void __maybe_unused __ssp_wait_for_xmitr(struct sifive_serial_port *ssp)
+{
+	while (sifive_serial_is_txfifo_full(ssp))
+		udelay(1); /* XXX Could probably be more intelligent here */
+}
+
+/*
+ * Linux serial API functions
+ */
+
+static void sifive_serial_stop_tx(struct uart_port *port)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_disable_txwm(ssp);
+}
+
+static void sifive_serial_stop_rx(struct uart_port *port)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_disable_rxwm(ssp);
+}
+
+static void sifive_serial_start_tx(struct uart_port *port)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_enable_txwm(ssp);
+}
+
+static irqreturn_t sifive_serial_irq(int irq, void *dev_id)
+{
+	struct sifive_serial_port *ssp = dev_id;
+	u32 ip;
+
+	spin_lock(&ssp->port.lock);
+
+	ip = __ssp_readl(ssp, SIFIVE_SERIAL_IP_OFFS);
+	if (!ip) {
+		spin_unlock(&ssp->port.lock);
+		return IRQ_NONE;
+	}
+
+	if (ip & SIFIVE_SERIAL_IP_RXWM_MASK)
+		__ssp_receive_chars(ssp);
+	if (ip & SIFIVE_SERIAL_IP_TXWM_MASK)
+		__ssp_transmit_chars(ssp);
+
+	spin_unlock(&ssp->port.lock);
+
+	return IRQ_HANDLED;
+}
+
+static unsigned int sifive_serial_tx_empty(struct uart_port *port)
+{
+	return TIOCSER_TEMT;
+}
+
+static unsigned int sifive_serial_get_mctrl(struct uart_port *port)
+{
+	return TIOCM_CAR | TIOCM_CTS | TIOCM_DSR;
+}
+
+static void sifive_serial_set_mctrl(struct uart_port *port, unsigned int mctrl)
+{
+	/* IP block does not support these signals */
+}
+
+static void sifive_serial_break_ctl(struct uart_port *port, int break_state)
+{
+	/* IP block does not support sending a break */
+}
+
+static int sifive_serial_startup(struct uart_port *port)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_enable_rxwm(ssp);
+
+	return 0;
+}
+
+static void sifive_serial_shutdown(struct uart_port *port)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_disable_rxwm(ssp);
+	__ssp_disable_txwm(ssp);
+}
+
+/**
+ * sifive_serial_clk_notifier() - clock post-rate-change notifier
+ * @nb: pointer to the struct notifier_block, from the notifier code
+ * @event: event mask from the notifier code
+ * @data: pointer to the struct clk_notifier_data from the notifier code
+ *
+ * On the V0 SoC, the UART IP block is derived from the CPU clock source
+ * after a synchronous divide-by-two divider, so any CPU clock rate change
+ * requires the UART baud rate to be updated.  This presumably could corrupt any
+ * serial word currently being transmitted or received.  It would probably
+ * be better to stop receives and transmits, then complete the baud rate
+ * change, then re-enable them.
+ */
+static int sifive_serial_clk_notifier(struct notifier_block *nb,
+				      unsigned long event, void *data)
+{
+	struct clk_notifier_data *cnd = data;
+	struct sifive_serial_port *ssp = notifier_to_sifive_serial_port(nb);
+
+	if (event == POST_RATE_CHANGE && ssp->clkin_rate != cnd->new_rate) {
+		ssp->clkin_rate = cnd->new_rate;
+		__ssp_update_div(ssp);
+	}
+
+	return NOTIFY_OK;
+}
+
+static void sifive_serial_set_termios(struct uart_port *port,
+				      struct ktermios *termios,
+				      struct ktermios *old)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+	unsigned long flags;
+	u32 v, old_v;
+	int rate;
+	char nstop;
+
+	if ((termios->c_cflag & CSIZE) != CS8) {
+		dev_err(ssp->port.dev, "only 8-bit words supported\n");
+		return;
+	}
+
+	/* Set number of stop bits */
+	nstop = (termios->c_cflag & CSTOPB) ? 2 : 1;
+	__ssp_set_stop_bits(ssp, nstop);
+
+	/* Set line rate */
+	rate = uart_get_baud_rate(port, termios, old, 0, ssp->clkin_rate / 16);
+	__ssp_update_baud_rate(ssp, rate);
+
+	spin_lock_irqsave(&ssp->port.lock, flags);
+
+	/*
+	 * Update the per-port timeout.
+	 */
+	uart_update_timeout(port, termios->c_cflag, rate);
+
+	ssp->port.read_status_mask = 0;
+	if (termios->c_iflag & INPCK) {
+		dev_err(ssp->port.dev, "INPCK flag not supported\n");
+		goto ssst_out;
+	}
+	if (termios->c_iflag & (BRKINT | PARMRK)) {
+		dev_err(ssp->port.dev, "BRKINT/PARMRK flag not supported\n");
+		goto ssst_out;
+	}
+
+	/*
+	 * ignore all characters if CREAD is not set
+	 */
+	v = __ssp_readl(ssp, SIFIVE_SERIAL_RXCTRL_OFFS);
+	old_v = v;
+	if ((termios->c_cflag & CREAD) == 0)
+		v &= SIFIVE_SERIAL_RXCTRL_RXEN_MASK;
+	else
+		v |= SIFIVE_SERIAL_RXCTRL_RXEN_MASK;
+	if (v != old_v)
+		__ssp_writel(v, SIFIVE_SERIAL_RXCTRL_OFFS, ssp);
+
+ssst_out:
+	spin_unlock_irqrestore(&ssp->port.lock, flags);
+}
+
+static void sifive_serial_release_port(struct uart_port *port)
+{
+}
+
+static int sifive_serial_request_port(struct uart_port *port)
+{
+	return 0;
+}
+
+static void sifive_serial_config_port(struct uart_port *port, int flags)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	ssp->port.type = PORT_SIFIVE_V0;
+}
+
+static int sifive_serial_verify_port(struct uart_port *port,
+				     struct serial_struct *ser)
+{
+	return -EINVAL;
+}
+
+static const char *sifive_serial_type(struct uart_port *port)
+{
+	return port->type == PORT_SIFIVE_V0 ? "SiFive UART v0" : NULL;
+}
+
+/*
+ * Early console support
+ */
+
+#ifdef CONFIG_SERIAL_EARLYCON
+static void early_sifive_serial_putc(struct uart_port *port, int c)
+{
+	while (__ssp_early_readl(port, SIFIVE_SERIAL_TXDATA_OFFS) &
+	       SIFIVE_SERIAL_TXDATA_FULL_MASK)
+		cpu_relax();
+
+	__ssp_early_writel(c, SIFIVE_SERIAL_TXDATA_OFFS, port);
+}
+
+static void early_sifive_serial_write(struct console *con, const char *s,
+				      unsigned int n)
+{
+	struct earlycon_device *dev = con->data;
+	struct uart_port *port = &dev->port;
+
+	uart_console_write(port, s, n, early_sifive_serial_putc);
+}
+
+static int __init early_sifive_serial_setup(struct earlycon_device *dev,
+					    const char *options)
+{
+	struct uart_port *port = &dev->port;
+
+	if (!port->membase)
+		return -ENODEV;
+
+	dev->con->write = early_sifive_serial_write;
+
+	return 0;
+}
+
+OF_EARLYCON_DECLARE(sifive, "sifive,uart0", early_sifive_serial_setup);
+OF_EARLYCON_DECLARE(sifive, "sifive,fu540-c000-uart0",
+		    early_sifive_serial_setup);
+#endif /* CONFIG_SERIAL_EARLYCON */
+
+/*
+ * Linux console interface
+ */
+
+#ifdef CONFIG_SERIAL_SIFIVE_CONSOLE
+
+static struct sifive_serial_port *sifive_serial_console_ports[SIFIVE_SERIAL_MAX_PORTS];
+
+static void sifive_serial_console_putchar(struct uart_port *port, int ch)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_wait_for_xmitr(ssp);
+	__ssp_transmit_char(ssp, ch);
+}
+
+static void sifive_serial_console_write(struct console *co, const char *s,
+					unsigned int count)
+{
+	struct sifive_serial_port *ssp = sifive_serial_console_ports[co->index];
+	unsigned long flags;
+	unsigned int ier;
+	int locked = 1;
+
+	if (!ssp)
+		return;
+
+	local_irq_save(flags);
+	if (ssp->port.sysrq)
+		locked = 0;
+	else if (oops_in_progress)
+		locked = spin_trylock(&ssp->port.lock);
+	else
+		spin_lock(&ssp->port.lock);
+
+	ier = __ssp_readl(ssp, SIFIVE_SERIAL_IE_OFFS);
+	__ssp_writel(0, SIFIVE_SERIAL_IE_OFFS, ssp);
+
+	uart_console_write(&ssp->port, s, count, sifive_serial_console_putchar);
+
+	__ssp_writel(ier, SIFIVE_SERIAL_IE_OFFS, ssp);
+
+	if (locked)
+		spin_unlock(&ssp->port.lock);
+	local_irq_restore(flags);
+}
+
+static int __init sifive_serial_console_setup(struct console *co, char *options)
+{
+	struct sifive_serial_port *ssp;
+	int baud = SIFIVE_DEFAULT_BAUD_RATE;
+	int bits = 8;
+	int parity = 'n';
+	int flow = 'n';
+
+	if (co->index < 0 || co->index >= SIFIVE_SERIAL_MAX_PORTS)
+		return -ENODEV;
+
+	ssp = sifive_serial_console_ports[co->index];
+	if (!ssp)
+		return -ENODEV;
+
+	if (options)
+		uart_parse_options(options, &baud, &parity, &bits, &flow);
+
+	return uart_set_options(&ssp->port, co, baud, parity, bits, flow);
+}
+
+static struct uart_driver sifive_serial_uart_driver;
+
+static struct console sifive_serial_console = {
+	.name		= SIFIVE_TTY_PREFIX,
+	.write		= sifive_serial_console_write,
+	.device		= uart_console_device,
+	.setup		= sifive_serial_console_setup,
+	.flags		= CON_PRINTBUFFER,
+	.index		= -1,
+	.data		= &sifive_serial_uart_driver,
+};
+
+static int __init sifive_console_init(void)
+{
+	register_console(&sifive_serial_console);
+	return 0;
+}
+
+console_initcall(sifive_console_init);
+
+static void __ssp_add_console_port(struct sifive_serial_port *ssp)
+{
+	sifive_serial_console_ports[ssp->port.line] = ssp;
+}
+
+static void __ssp_remove_console_port(struct sifive_serial_port *ssp)
+{
+	sifive_serial_console_ports[ssp->port.line] = 0;
+}
+
+#define SIFIVE_SERIAL_CONSOLE	(&sifive_serial_console)
+
+#else
+
+#define SIFIVE_SERIAL_CONSOLE	NULL
+
+static inline void __ssp_add_console_port(struct sifive_serial_port *ssp)
+{}
+static void __ssp_remove_console_port(struct sifive_serial_port *ssp)
+{}
+
+#endif
+
+static const struct uart_ops sifive_serial_uops = {
+	.tx_empty	= sifive_serial_tx_empty,
+	.set_mctrl	= sifive_serial_set_mctrl,
+	.get_mctrl	= sifive_serial_get_mctrl,
+	.stop_tx	= sifive_serial_stop_tx,
+	.start_tx	= sifive_serial_start_tx,
+	.stop_rx	= sifive_serial_stop_rx,
+	.break_ctl	= sifive_serial_break_ctl,
+	.startup	= sifive_serial_startup,
+	.shutdown	= sifive_serial_shutdown,
+	.set_termios	= sifive_serial_set_termios,
+	.type		= sifive_serial_type,
+	.release_port	= sifive_serial_release_port,
+	.request_port	= sifive_serial_request_port,
+	.config_port	= sifive_serial_config_port,
+	.verify_port	= sifive_serial_verify_port,
+};
+
+static struct uart_driver sifive_serial_uart_driver = {
+	.owner		= THIS_MODULE,
+	.driver_name	= SIFIVE_SERIAL_NAME,
+	.dev_name	= SIFIVE_TTY_PREFIX,
+	.nr		= SIFIVE_SERIAL_MAX_PORTS,
+	.cons		= SIFIVE_SERIAL_CONSOLE,
+};
+
+static int sifive_serial_probe(struct platform_device *pdev)
+{
+	struct sifive_serial_port *ssp;
+	struct resource *mem;
+	struct clk *clk;
+	void __iomem *base;
+	int irq, id, r;
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0) {
+		dev_err(&pdev->dev, "could not acquire interrupt\n");
+		return -EPROBE_DEFER;
+	}
+
+	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	base = devm_ioremap_resource(&pdev->dev, mem);
+	if (IS_ERR(base)) {
+		dev_err(&pdev->dev, "could not acquire device memory\n");
+		return PTR_ERR(base);
+	}
+
+	clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(clk)) {
+		dev_err(&pdev->dev, "unable to find controller clock\n");
+		return PTR_ERR(clk);
+	}
+
+	id = of_alias_get_id(pdev->dev.of_node, "serial");
+	if (id < 0) {
+		dev_err(&pdev->dev, "missing aliases entry\n");
+		return id;
+	}
+
+#ifdef CONFIG_SERIAL_SIFIVE_CONSOLE
+	if (id > SIFIVE_SERIAL_MAX_PORTS) {
+		dev_err(&pdev->dev, "too many UARTs (%d)\n", id);
+		return -EINVAL;
+	}
+#endif
+
+	ssp = devm_kzalloc(&pdev->dev, sizeof(*ssp), GFP_KERNEL);
+	if (!ssp)
+		return -ENOMEM;
+
+	ssp->port.dev = &pdev->dev;
+	ssp->port.type = PORT_SIFIVE_V0;
+	ssp->port.iotype = UPIO_MEM;
+	ssp->port.irq = irq;
+	ssp->port.fifosize = SIFIVE_TX_FIFO_DEPTH;
+	ssp->port.ops = &sifive_serial_uops;
+	ssp->port.line = id;
+	ssp->port.mapbase = mem->start;
+	ssp->port.membase = base;
+	ssp->dev = &pdev->dev;
+	ssp->clk = clk;
+	ssp->clk_notifier.notifier_call = sifive_serial_clk_notifier;
+
+	r = clk_notifier_register(ssp->clk, &ssp->clk_notifier);
+	if (r) {
+		dev_err(&pdev->dev, "could not register clock notifier: %d\n",
+			r);
+		goto probe_out1;
+	}
+
+	/* Set up clock divider */
+	ssp->clkin_rate = clk_get_rate(ssp->clk);
+	ssp->baud_rate = SIFIVE_DEFAULT_BAUD_RATE;
+	__ssp_update_div(ssp);
+
+	platform_set_drvdata(pdev, ssp);
+
+	/* Enable transmits and set the watermark level to 1 */
+	__ssp_writel((1 << SIFIVE_SERIAL_TXCTRL_TXCNT_SHIFT) |
+		     SIFIVE_SERIAL_TXCTRL_TXEN_MASK,
+		     SIFIVE_SERIAL_TXCTRL_OFFS, ssp);
+
+	/* Enable receives and set the watermark level to 0 */
+	__ssp_writel((0 << SIFIVE_SERIAL_RXCTRL_RXCNT_SHIFT) |
+		     SIFIVE_SERIAL_RXCTRL_RXEN_MASK,
+		     SIFIVE_SERIAL_RXCTRL_OFFS, ssp);
+
+	r = request_irq(ssp->port.irq, sifive_serial_irq, ssp->port.irqflags,
+			dev_name(&pdev->dev), ssp);
+	if (r) {
+		dev_err(&pdev->dev, "could not attach interrupt: %d\n", r);
+		goto probe_out2;
+	}
+
+	__ssp_add_console_port(ssp);
+
+	r = uart_add_one_port(&sifive_serial_uart_driver, &ssp->port);
+	if (r != 0) {
+		dev_err(&pdev->dev, "could not add uart: %d\n", r);
+		goto probe_out3;
+	}
+
+	return 0;
+
+probe_out3:
+	__ssp_remove_console_port(ssp);
+	free_irq(ssp->port.irq, ssp);
+probe_out2:
+	clk_notifier_unregister(ssp->clk, &ssp->clk_notifier);
+probe_out1:
+	return r;
+}
+
+static int sifive_serial_remove(struct platform_device *dev)
+{
+	struct sifive_serial_port *ssp = platform_get_drvdata(dev);
+
+	__ssp_remove_console_port(ssp);
+	uart_remove_one_port(&sifive_serial_uart_driver, &ssp->port);
+	free_irq(ssp->port.irq, ssp);
+	clk_notifier_unregister(ssp->clk, &ssp->clk_notifier);
+
+	return 0;
+}
+
+static const struct of_device_id sifive_serial_of_match[] = {
+	{ .compatible = "sifive,fu540-c000-uart0" },
+	{ .compatible = "sifive,uart0" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, sifive_serial_of_match);
+
+static struct platform_driver sifive_serial_platform_driver = {
+	.probe		= sifive_serial_probe,
+	.remove		= sifive_serial_remove,
+	.driver		= {
+		.name	= SIFIVE_SERIAL_NAME,
+		.of_match_table = of_match_ptr(sifive_serial_of_match),
+	},
+};
+
+static int __init sifive_serial_init(void)
+{
+	int r;
+
+	r = uart_register_driver(&sifive_serial_uart_driver);
+	if (r)
+		goto init_out1;
+
+	r = platform_driver_register(&sifive_serial_platform_driver);
+	if (r)
+		goto init_out2;
+
+	return 0;
+
+init_out2:
+	uart_unregister_driver(&sifive_serial_uart_driver);
+init_out1:
+	return r;
+}
+
+static void __exit sifive_serial_exit(void)
+{
+	platform_driver_unregister(&sifive_serial_platform_driver);
+	uart_unregister_driver(&sifive_serial_uart_driver);
+}
+
+module_init(sifive_serial_init);
+module_exit(sifive_serial_exit);
+
+MODULE_DESCRIPTION("SiFive UART serial driver");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Paul Walmsley <paul@pwsan.com>");
diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h
index dce5f9dae121..569d5172d23c 100644
--- a/include/uapi/linux/serial_core.h
+++ b/include/uapi/linux/serial_core.h
@@ -281,4 +281,7 @@
 /* MediaTek BTIF */
 #define PORT_MTK_BTIF	117
 
+/* SiFive UART */
+#define PORT_SIFIVE_V0	118
+
 #endif /* _UAPILINUX_SERIAL_CORE_H */
-- 
2.19.1

[PATCH v3 2/2] tty: serial: add driver for the SiFive UART

[Paul Walmsley]

Add a serial driver for the SiFive UART, found on SiFive FU540 devices
(among others).

The underlying serial IP block is relatively basic, and currently does
not support serial break detection.  Further information on the IP
block can be found in the documentation and Chisel sources:

https://static.dev.sifive.com/FU540-C000-v1.0.pdf

https://github.com/sifive/sifive-blocks/tree/master/src/main/scala/devices/uart

This driver was written in collaboration with Wesley Terpstra
<wesley@sifive.com>.

Boot-tested on a SiFive HiFive Unleashed A00 board.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Wesley Terpstra <wesley@sifive.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-riscv@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
---
v3: fix MODULE_DEVICE_TABLE argument
v2: remove leftover junk related to CONFIG_CONSOLE_POLL; add missing
    spin_unlock() in ISR found by 0-day and Julia Lawall

 drivers/tty/serial/Kconfig       |   24 +
 drivers/tty/serial/Makefile      |    1 +
 drivers/tty/serial/sifive.c      | 1067 ++++++++++++++++++++++++++++++
 include/uapi/linux/serial_core.h |    3 +
 4 files changed, 1095 insertions(+)
 create mode 100644 drivers/tty/serial/sifive.c

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index df8bd0c7b97d..fdd624df75c8 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1060,6 +1060,30 @@ config SERIAL_OMAP_CONSOLE
 	  your boot loader about how to pass options to the kernel at
 	  boot time.)
 
+config SERIAL_SIFIVE
+	tristate "SiFive UART support"
+	depends on OF
+	select SERIAL_CORE
+	help
+	  Select this option if you are building a kernel for a device that
+	  contains a SiFive UART IP block.  This type of UART is present on
+	  SiFive FU540 SoCs, among others.
+
+config SERIAL_SIFIVE_CONSOLE
+	bool "Console on SiFive UART"
+	depends on SERIAL_SIFIVE=y
+	select SERIAL_CORE_CONSOLE
+	help
+	  Select this option if you would like to use a SiFive UART as the
+	  system console.
+
+	  Even if you say Y here, the currently visible virtual console
+	  (/dev/tty0) will still be used as the system console by default, but
+	  you can alter that using a kernel command line option such as
+	  "console=ttySIFx". (Try "man bootparam" or see the documentation of
+	  your boot loader about how to pass options to the kernel at
+	  boot time.)
+
 config SERIAL_LANTIQ
 	bool "Lantiq serial driver"
 	depends on LANTIQ
diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index daac675612df..7e906d3c0455 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile
@@ -89,6 +89,7 @@ obj-$(CONFIG_SERIAL_MVEBU_UART)	+= mvebu-uart.o
 obj-$(CONFIG_SERIAL_PIC32)	+= pic32_uart.o
 obj-$(CONFIG_SERIAL_MPS2_UART)	+= mps2-uart.o
 obj-$(CONFIG_SERIAL_OWL)	+= owl-uart.o
+obj-$(CONFIG_SERIAL_SIFIVE)	+= sifive.o
 
 # GPIOLIB helpers for modem control lines
 obj-$(CONFIG_SERIAL_MCTRL_GPIO)	+= serial_mctrl_gpio.o
diff --git a/drivers/tty/serial/sifive.c b/drivers/tty/serial/sifive.c
new file mode 100644
index 000000000000..80c06039fb57
--- /dev/null
+++ b/drivers/tty/serial/sifive.c
@@ -0,0 +1,1067 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * SiFive UART driver
+ * Copyright (C) 2018 Paul Walmsley <paul@pwsan.com>
+ * Copyright (C) 2018 SiFive
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * Based partially on:
+ * - drivers/tty/serial/pxa.c
+ * - drivers/tty/serial/amba-pl011.c
+ * - drivers/tty/serial/uartlite.c
+ * - drivers/tty/serial/omap-serial.c
+ * - drivers/pwm/pwm-sifive.c
+ *
+ * See the following sources for further documentation:
+ * - Chapter 19 "Universal Asynchronous Receiver/Transmitter (UART)" of
+ *   SiFive FE310-G000 v2p3
+ * - The tree/master/src/main/scala/devices/uart directory of
+ *   https://github.com/sifive/sifive-blocks/
+ *
+ * The SiFive UART design is not 8250-compatible.  The following common
+ * features are not supported:
+ * - Word lengths other than 8 bits
+ * - Break handling
+ * - Parity
+ * - Flow control
+ * - Modem signals (DSR, RI, etc.)
+ * On the other hand, the design is free from the baggage of the 8250
+ * programming model.
+ */
+
+#include <linux/clk.h>
+#include <linux/console.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/irq.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/platform_device.h>
+#include <linux/serial_core.h>
+#include <linux/serial_reg.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+
+/*
+ * Register offsets
+ */
+
+/* TXDATA */
+#define SIFIVE_SERIAL_TXDATA_OFFS		0x0
+#define SIFIVE_SERIAL_TXDATA_FULL_SHIFT		31
+#define SIFIVE_SERIAL_TXDATA_FULL_MASK		(1 << SIFIVE_SERIAL_TXDATA_FULL_SHIFT)
+#define SIFIVE_SERIAL_TXDATA_DATA_SHIFT		0
+#define SIFIVE_SERIAL_TXDATA_DATA_MASK		(0xff << SIFIVE_SERIAL_TXDATA_DATA_SHIFT)
+
+/* RXDATA */
+#define SIFIVE_SERIAL_RXDATA_OFFS		0x4
+#define SIFIVE_SERIAL_RXDATA_EMPTY_SHIFT	31
+#define SIFIVE_SERIAL_RXDATA_EMPTY_MASK		(1 << SIFIVE_SERIAL_RXDATA_EMPTY_SHIFT)
+#define SIFIVE_SERIAL_RXDATA_DATA_SHIFT		0
+#define SIFIVE_SERIAL_RXDATA_DATA_MASK		(0xff << SIFIVE_SERIAL_RXDATA_DATA_SHIFT)
+
+/* TXCTRL */
+#define SIFIVE_SERIAL_TXCTRL_OFFS		0x8
+#define SIFIVE_SERIAL_TXCTRL_TXCNT_SHIFT	16
+#define SIFIVE_SERIAL_TXCTRL_TXCNT_MASK		(0x7 << SIFIVE_SERIAL_TXCTRL_TXCNT_SHIFT)
+#define SIFIVE_SERIAL_TXCTRL_NSTOP_SHIFT	1
+#define SIFIVE_SERIAL_TXCTRL_NSTOP_MASK		(1 << SIFIVE_SERIAL_TXCTRL_NSTOP_SHIFT)
+#define SIFIVE_SERIAL_TXCTRL_TXEN_SHIFT		0
+#define SIFIVE_SERIAL_TXCTRL_TXEN_MASK		(1 << SIFIVE_SERIAL_TXCTRL_TXEN_SHIFT)
+
+/* RXCTRL */
+#define SIFIVE_SERIAL_RXCTRL_OFFS		0xC
+#define SIFIVE_SERIAL_RXCTRL_RXCNT_SHIFT	16
+#define SIFIVE_SERIAL_RXCTRL_RXCNT_MASK		(0x7 << SIFIVE_SERIAL_TXCTRL_TXCNT_SHIFT)
+#define SIFIVE_SERIAL_RXCTRL_RXEN_SHIFT		0
+#define SIFIVE_SERIAL_RXCTRL_RXEN_MASK		(1 << SIFIVE_SERIAL_RXCTRL_RXEN_SHIFT)
+
+/* IE */
+#define SIFIVE_SERIAL_IE_OFFS			0x10
+#define SIFIVE_SERIAL_IE_RXWM_SHIFT		1
+#define SIFIVE_SERIAL_IE_RXWM_MASK		(1 << SIFIVE_SERIAL_IE_RXWM_SHIFT)
+#define SIFIVE_SERIAL_IE_TXWM_SHIFT		0
+#define SIFIVE_SERIAL_IE_TXWM_MASK		(1 << SIFIVE_SERIAL_IE_TXWM_SHIFT)
+
+/* IP */
+#define SIFIVE_SERIAL_IP_OFFS			0x14
+#define SIFIVE_SERIAL_IP_RXWM_SHIFT		1
+#define SIFIVE_SERIAL_IP_RXWM_MASK		(1 << SIFIVE_SERIAL_IP_RXWM_SHIFT)
+#define SIFIVE_SERIAL_IP_TXWM_SHIFT		0
+#define SIFIVE_SERIAL_IP_TXWM_MASK		(1 << SIFIVE_SERIAL_IP_TXWM_SHIFT)
+
+/* DIV */
+#define SIFIVE_SERIAL_DIV_OFFS			0x18
+#define SIFIVE_SERIAL_DIV_DIV_SHIFT		0
+#define SIFIVE_SERIAL_DIV_DIV_MASK		(0xffff << SIFIVE_SERIAL_IP_DIV_SHIFT)
+
+/*
+ * Config macros
+ */
+
+/*
+ * SIFIVE_SERIAL_MAX_PORTS: maximum number of UARTs on a device that can
+ *                          host a serial console
+ */
+#define SIFIVE_SERIAL_MAX_PORTS			8
+
+/*
+ * SIFIVE_DEFAULT_BAUD_RATE: default baud rate that the driver should
+ *                           configure itself to use
+ */
+#define SIFIVE_DEFAULT_BAUD_RATE		115200
+
+/* SIFIVE_SERIAL_NAME: our driver's name that we pass to the operating system */
+#define SIFIVE_SERIAL_NAME			"sifive-serial"
+
+/* SIFIVE_TTY_PREFIX: tty name prefix for SiFive serial ports */
+#define SIFIVE_TTY_PREFIX			"ttySIF"
+
+/* SIFIVE_TX_FIFO_DEPTH: depth of the TX FIFO (in bytes) */
+#define SIFIVE_TX_FIFO_DEPTH			8
+
+/* SIFIVE_RX_FIFO_DEPTH: depth of the TX FIFO (in bytes) */
+#define SIFIVE_RX_FIFO_DEPTH			8
+
+#if (SIFIVE_TX_FIFO_DEPTH != SIFIVE_RX_FIFO_DEPTH)
+#error Driver does not support configurations with different TX, RX FIFO sizes
+#endif
+
+/*
+ *
+ */
+
+/**
+ * sifive_serial_port - driver-specific data extension to struct uart_port
+ * @port: struct uart_port embedded in this struct
+ * @dev: struct device *
+ * @ier: shadowed copy of the interrupt enable register
+ * @clkin_rate: input clock to the UART IP block.
+ * @baud_rate: UART serial line rate (e.g., 115200 baud)
+ * @clk_notifier: clock rate change notifier for upstream clock changes
+ *
+ * Configuration data specific to this SiFive UART.
+ */
+struct sifive_serial_port {
+	struct uart_port	port;
+	struct device		*dev;
+	unsigned char		ier;
+	unsigned long		clkin_rate;
+	unsigned long		baud_rate;
+	struct clk		*clk;
+	struct notifier_block	clk_notifier;
+};
+
+/*
+ * Structure container-of macros
+ */
+
+#define port_to_sifive_serial_port(p) (container_of((p), \
+						    struct sifive_serial_port, \
+						    port))
+
+#define notifier_to_sifive_serial_port(nb) (container_of((nb), \
+							 struct sifive_serial_port, \
+							 clk_notifier))
+
+/*
+ * Forward declarations
+ */
+static void sifive_serial_stop_tx(struct uart_port *port);
+
+/*
+ * Internal functions
+ */
+
+/**
+ * __ssp_early_writel() - write to a SiFive serial port register (early)
+ * @port: pointer to a struct uart_port record
+ * @offs: register address offset from the IP block base address
+ * @v: value to write to the register
+ *
+ * Given a pointer @port to a struct uart_port record, write the value
+ * @v to the IP block register address offset @offs.  This function is
+ * intended for early console use.
+ *
+ * Context: Intended to be used only by the earlyconsole code.
+ */
+static void __ssp_early_writel(u32 v, u16 offs, struct uart_port *port)
+{
+	writel_relaxed(v, port->membase + offs);
+}
+
+/**
+ * __ssp_early_readl() - read from a SiFive serial port register (early)
+ * @port: pointer to a struct uart_port record
+ * @offs: register address offset from the IP block base address
+ *
+ * Given a pointer @port to a struct uart_port record, read the
+ * contents of the IP block register located at offset @offs from the
+ * IP block base and return it.  This function is intended for early
+ * console use.
+ *
+ * Context: Intended to be called only by the earlyconsole code or by
+ *          __ssp_readl() or __ssp_writel() (in this driver)
+ *
+ * Returns: the register value read from the UART.
+ */
+static u32 __ssp_early_readl(struct uart_port *port, u16 offs)
+{
+	return readl_relaxed(port->membase + offs);
+}
+
+/**
+ * __ssp_writel() - write to a SiFive serial port register
+ * @v: value to write to the register
+ * @offs: register address offset from the IP block base address
+ * @ssp: pointer to a struct sifive_serial_port record
+ *
+ * Write the value @v to the IP block register located at offset @offs from the
+ * IP block base, given a pointer @ssp to a struct sifive_serial_port record.
+ *
+ * Context: Any context.
+ */
+static void __ssp_writel(u32 v, u16 offs, struct sifive_serial_port *ssp)
+{
+	__ssp_early_writel(v, offs, &ssp->port);
+}
+
+/**
+ * __ssp_readl() - read from a SiFive serial port register
+ * @ssp: pointer to a struct sifive_serial_port record
+ * @offs: register address offset from the IP block base address
+ *
+ * Read the contents of the IP block register located at offset @offs from the
+ * IP block base, given a pointer @ssp to a struct sifive_serial_port record.
+ *
+ * Context: Any context.
+ *
+ * Returns: the value of the UART register
+ */
+static u32 __ssp_readl(struct sifive_serial_port *ssp, u16 offs)
+{
+	return __ssp_early_readl(&ssp->port, offs);
+}
+
+/**
+ * sifive_serial_is_txfifo_full() - is the TXFIFO full?
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Read the transmit FIFO "full" bit, returning a non-zero value if the
+ * TX FIFO is full, or zero if space remains.  Intended to be used to prevent
+ * writes to the TX FIFO when it's full.
+ *
+ * Returns: SIFIVE_SERIAL_TXDATA_FULL_MASK (non-zero) if the transmit FIFO
+ * is full, or 0 if space remains.
+ */
+static int sifive_serial_is_txfifo_full(struct sifive_serial_port *ssp)
+{
+	return __ssp_readl(ssp, SIFIVE_SERIAL_TXDATA_OFFS) &
+		SIFIVE_SERIAL_TXDATA_FULL_MASK;
+}
+
+/**
+ * __ssp_transmit_char() - enqueue a byte to transmit onto the TX FIFO
+ * @ssp: pointer to a struct sifive_serial_port
+ * @ch: character to transmit
+ *
+ * Enqueue a byte @ch onto the transmit FIFO, given a pointer @ssp to the
+ * struct sifive_serial_port * to transmit on.  Caller should first check to
+ * ensure that the TXFIFO has space; see sifive_serial_is_txfifo_full().
+ *
+ * Context: Any context.
+ */
+static void __ssp_transmit_char(struct sifive_serial_port *ssp, int ch)
+{
+	__ssp_writel(ch, SIFIVE_SERIAL_TXDATA_OFFS, ssp);
+}
+
+/**
+ * __ssp_transmit_chars() - enqueue multiple bytes onto the TX FIFO
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Transfer up to a TX FIFO size's worth of characters from the Linux serial
+ * transmit buffer to the SiFive UART TX FIFO.
+ *
+ * Context: Any context.  Expects @ssp->port.lock to be held by caller.
+ */
+static void __ssp_transmit_chars(struct sifive_serial_port *ssp)
+{
+	struct circ_buf *xmit = &ssp->port.state->xmit;
+	int count;
+
+	if (ssp->port.x_char) {
+		__ssp_transmit_char(ssp, ssp->port.x_char);
+		ssp->port.icount.tx++;
+		ssp->port.x_char = 0;
+		return;
+	}
+	if (uart_circ_empty(xmit) || uart_tx_stopped(&ssp->port)) {
+		sifive_serial_stop_tx(&ssp->port);
+		return;
+	}
+	count = SIFIVE_TX_FIFO_DEPTH;
+	do {
+		__ssp_transmit_char(ssp, xmit->buf[xmit->tail]);
+		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
+		ssp->port.icount.tx++;
+		if (uart_circ_empty(xmit))
+			break;
+	} while (--count > 0);
+
+	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+		uart_write_wakeup(&ssp->port);
+
+	if (uart_circ_empty(xmit))
+		sifive_serial_stop_tx(&ssp->port);
+}
+
+/**
+ * __ssp_enable_txwm() - enable transmit watermark interrupts
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Enable interrupt generation when the transmit FIFO watermark is reached
+ * on the SiFive UART referred to by @ssp.
+ */
+static void __ssp_enable_txwm(struct sifive_serial_port *ssp)
+{
+	if (ssp->ier & SIFIVE_SERIAL_IE_TXWM_MASK)
+		return;
+
+	ssp->ier |= SIFIVE_SERIAL_IE_TXWM_MASK;
+	__ssp_writel(ssp->ier, SIFIVE_SERIAL_IE_OFFS, ssp);
+}
+
+/**
+ * __ssp_enable_rxwm() - enable receive watermark interrupts
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Enable interrupt generation when the receive FIFO watermark is reached
+ * on the SiFive UART referred to by @ssp.
+ */
+static void __ssp_enable_rxwm(struct sifive_serial_port *ssp)
+{
+	if (ssp->ier & SIFIVE_SERIAL_IE_RXWM_MASK)
+		return;
+
+	ssp->ier |= SIFIVE_SERIAL_IE_RXWM_MASK;
+	__ssp_writel(ssp->ier, SIFIVE_SERIAL_IE_OFFS, ssp);
+}
+
+/**
+ * __ssp_disable_txwm() - disable transmit watermark interrupts
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Disable interrupt generation when the transmit FIFO watermark is reached
+ * on the UART referred to by @ssp.
+ */
+static void __ssp_disable_txwm(struct sifive_serial_port *ssp)
+{
+	if (!(ssp->ier & SIFIVE_SERIAL_IE_TXWM_MASK))
+		return;
+
+	ssp->ier &= ~SIFIVE_SERIAL_IE_TXWM_MASK;
+	__ssp_writel(ssp->ier, SIFIVE_SERIAL_IE_OFFS, ssp);
+}
+
+/**
+ * __ssp_disable_rxwm() - disable receive watermark interrupts
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Disable interrupt generation when the receive FIFO watermark is reached
+ * on the UART referred to by @ssp.
+ */
+static void __ssp_disable_rxwm(struct sifive_serial_port *ssp)
+{
+	if (!(ssp->ier & SIFIVE_SERIAL_IE_RXWM_MASK))
+		return;
+
+	ssp->ier &= ~SIFIVE_SERIAL_IE_RXWM_MASK;
+	__ssp_writel(ssp->ier, SIFIVE_SERIAL_IE_OFFS, ssp);
+}
+
+/**
+ * __ssp_receive_char() - receive a byte from the UART
+ * @ssp: pointer to a struct sifive_serial_port
+ * @is_empty: char pointer to return whether the RX FIFO is empty
+ *
+ * Try to read a byte from the SiFive UART RX FIFO, referenced by
+ * @ssp, and to return it.  Also returns the RX FIFO empty bit in
+ * the char pointed to by @ch.  The caller must pass the byte back to the
+ * Linux serial layer if needed.
+ *
+ * Returns: the byte read from the UART RX FIFO.
+ */
+static char __ssp_receive_char(struct sifive_serial_port *ssp, char *is_empty)
+{
+	u32 v;
+	u8 ch;
+
+	v = __ssp_readl(ssp, SIFIVE_SERIAL_RXDATA_OFFS);
+
+	if (!is_empty)
+		WARN_ON(1);
+	else
+		*is_empty = (v & SIFIVE_SERIAL_RXDATA_EMPTY_MASK) >>
+			SIFIVE_SERIAL_RXDATA_EMPTY_SHIFT;
+
+	ch = (v & SIFIVE_SERIAL_RXDATA_DATA_MASK) >>
+		SIFIVE_SERIAL_RXDATA_DATA_SHIFT;
+
+	return ch;
+}
+
+/**
+ * __ssp_receive_chars() - receive multiple bytes from the UART
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Receive up to an RX FIFO's worth of bytes from the SiFive UART referred
+ * to by @ssp and pass them up to the Linux serial layer.
+ *
+ * Context: Expects ssp->port.lock to be held by caller.
+ */
+static void __ssp_receive_chars(struct sifive_serial_port *ssp)
+{
+	unsigned char ch;
+	char is_empty;
+	int c;
+
+	for (c = SIFIVE_RX_FIFO_DEPTH; c > 0; --c) {
+		ch = __ssp_receive_char(ssp, &is_empty);
+		if (is_empty)
+			break;
+
+		ssp->port.icount.rx++;
+		uart_insert_char(&ssp->port, 0, 0, ch, TTY_NORMAL);
+	}
+
+	spin_unlock(&ssp->port.lock);
+	tty_flip_buffer_push(&ssp->port.state->port);
+	spin_lock(&ssp->port.lock);
+}
+
+/**
+ * __ssp_update_div() - calculate the divisor setting by the line rate
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Calculate the appropriate value of the clock divisor for the UART
+ * and target line rate referred to by @ssp and write it into the
+ * hardware.
+ */
+static void __ssp_update_div(struct sifive_serial_port *ssp)
+{
+	u16 div;
+
+	div = DIV_ROUND_UP(ssp->clkin_rate, ssp->baud_rate) - 1;
+
+	__ssp_writel(div, SIFIVE_SERIAL_DIV_OFFS, ssp);
+}
+
+/**
+ * __ssp_update_baud_rate() - set the UART "baud rate"
+ * @ssp: pointer to a struct sifive_serial_port
+ * @rate: new target bit rate
+ *
+ * Calculate the UART divisor value for the target bit rate @rate for the
+ * SiFive UART described by @ssp and program it into the UART.  There may
+ * be some error between the target bit rate and the actual bit rate implemented
+ * by the UART due to clock ratio granularity.
+ */
+static void __ssp_update_baud_rate(struct sifive_serial_port *ssp,
+				   unsigned int rate)
+{
+	if (ssp->baud_rate == rate)
+		return;
+
+	ssp->baud_rate = rate;
+	__ssp_update_div(ssp);
+}
+
+/**
+ * __ssp_set_stop_bits() - set the number of stop bits
+ * @ssp: pointer to a struct sifive_serial_port
+ * @nstop: 1 or 2 (stop bits)
+ *
+ * Program the SiFive UART referred to by @ssp to use @nstop stop bits.
+ */
+static void __ssp_set_stop_bits(struct sifive_serial_port *ssp, char nstop)
+{
+	u32 v;
+
+	if (nstop < 1 || nstop > 2) {
+		WARN_ON(1);
+		return;
+	}
+
+	v = __ssp_readl(ssp, SIFIVE_SERIAL_TXCTRL_OFFS);
+	v &= ~SIFIVE_SERIAL_TXCTRL_NSTOP_MASK;
+	v |= (nstop - 1) << SIFIVE_SERIAL_TXCTRL_NSTOP_SHIFT;
+	__ssp_writel(v, SIFIVE_SERIAL_TXCTRL_OFFS, ssp);
+}
+
+/**
+ * __ssp_wait_for_xmitr() - wait for an empty slot on the TX FIFO
+ * @ssp: pointer to a struct sifive_serial_port
+ *
+ * Delay while the UART TX FIFO referred to by @ssp is marked as full.
+ *
+ * Context: Any context.
+ */
+static void __maybe_unused __ssp_wait_for_xmitr(struct sifive_serial_port *ssp)
+{
+	while (sifive_serial_is_txfifo_full(ssp))
+		udelay(1); /* XXX Could probably be more intelligent here */
+}
+
+/*
+ * Linux serial API functions
+ */
+
+static void sifive_serial_stop_tx(struct uart_port *port)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_disable_txwm(ssp);
+}
+
+static void sifive_serial_stop_rx(struct uart_port *port)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_disable_rxwm(ssp);
+}
+
+static void sifive_serial_start_tx(struct uart_port *port)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_enable_txwm(ssp);
+}
+
+static irqreturn_t sifive_serial_irq(int irq, void *dev_id)
+{
+	struct sifive_serial_port *ssp = dev_id;
+	u32 ip;
+
+	spin_lock(&ssp->port.lock);
+
+	ip = __ssp_readl(ssp, SIFIVE_SERIAL_IP_OFFS);
+	if (!ip) {
+		spin_unlock(&ssp->port.lock);
+		return IRQ_NONE;
+	}
+
+	if (ip & SIFIVE_SERIAL_IP_RXWM_MASK)
+		__ssp_receive_chars(ssp);
+	if (ip & SIFIVE_SERIAL_IP_TXWM_MASK)
+		__ssp_transmit_chars(ssp);
+
+	spin_unlock(&ssp->port.lock);
+
+	return IRQ_HANDLED;
+}
+
+static unsigned int sifive_serial_tx_empty(struct uart_port *port)
+{
+	return TIOCSER_TEMT;
+}
+
+static unsigned int sifive_serial_get_mctrl(struct uart_port *port)
+{
+	return TIOCM_CAR | TIOCM_CTS | TIOCM_DSR;
+}
+
+static void sifive_serial_set_mctrl(struct uart_port *port, unsigned int mctrl)
+{
+	/* IP block does not support these signals */
+}
+
+static void sifive_serial_break_ctl(struct uart_port *port, int break_state)
+{
+	/* IP block does not support sending a break */
+}
+
+static int sifive_serial_startup(struct uart_port *port)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_enable_rxwm(ssp);
+
+	return 0;
+}
+
+static void sifive_serial_shutdown(struct uart_port *port)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_disable_rxwm(ssp);
+	__ssp_disable_txwm(ssp);
+}
+
+/**
+ * sifive_serial_clk_notifier() - clock post-rate-change notifier
+ * @nb: pointer to the struct notifier_block, from the notifier code
+ * @event: event mask from the notifier code
+ * @data: pointer to the struct clk_notifier_data from the notifier code
+ *
+ * On the V0 SoC, the UART IP block is derived from the CPU clock source
+ * after a synchronous divide-by-two divider, so any CPU clock rate change
+ * requires the UART baud rate to be updated.  This presumably could corrupt any
+ * serial word currently being transmitted or received.  It would probably
+ * be better to stop receives and transmits, then complete the baud rate
+ * change, then re-enable them.
+ */
+static int sifive_serial_clk_notifier(struct notifier_block *nb,
+				      unsigned long event, void *data)
+{
+	struct clk_notifier_data *cnd = data;
+	struct sifive_serial_port *ssp = notifier_to_sifive_serial_port(nb);
+
+	if (event == POST_RATE_CHANGE && ssp->clkin_rate != cnd->new_rate) {
+		ssp->clkin_rate = cnd->new_rate;
+		__ssp_update_div(ssp);
+	}
+
+	return NOTIFY_OK;
+}
+
+static void sifive_serial_set_termios(struct uart_port *port,
+				      struct ktermios *termios,
+				      struct ktermios *old)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+	unsigned long flags;
+	u32 v, old_v;
+	int rate;
+	char nstop;
+
+	if ((termios->c_cflag & CSIZE) != CS8) {
+		dev_err(ssp->port.dev, "only 8-bit words supported\n");
+		return;
+	}
+
+	/* Set number of stop bits */
+	nstop = (termios->c_cflag & CSTOPB) ? 2 : 1;
+	__ssp_set_stop_bits(ssp, nstop);
+
+	/* Set line rate */
+	rate = uart_get_baud_rate(port, termios, old, 0, ssp->clkin_rate / 16);
+	__ssp_update_baud_rate(ssp, rate);
+
+	spin_lock_irqsave(&ssp->port.lock, flags);
+
+	/*
+	 * Update the per-port timeout.
+	 */
+	uart_update_timeout(port, termios->c_cflag, rate);
+
+	ssp->port.read_status_mask = 0;
+	if (termios->c_iflag & INPCK) {
+		dev_err(ssp->port.dev, "INPCK flag not supported\n");
+		goto ssst_out;
+	}
+	if (termios->c_iflag & (BRKINT | PARMRK)) {
+		dev_err(ssp->port.dev, "BRKINT/PARMRK flag not supported\n");
+		goto ssst_out;
+	}
+
+	/*
+	 * ignore all characters if CREAD is not set
+	 */
+	v = __ssp_readl(ssp, SIFIVE_SERIAL_RXCTRL_OFFS);
+	old_v = v;
+	if ((termios->c_cflag & CREAD) == 0)
+		v &= SIFIVE_SERIAL_RXCTRL_RXEN_MASK;
+	else
+		v |= SIFIVE_SERIAL_RXCTRL_RXEN_MASK;
+	if (v != old_v)
+		__ssp_writel(v, SIFIVE_SERIAL_RXCTRL_OFFS, ssp);
+
+ssst_out:
+	spin_unlock_irqrestore(&ssp->port.lock, flags);
+}
+
+static void sifive_serial_release_port(struct uart_port *port)
+{
+}
+
+static int sifive_serial_request_port(struct uart_port *port)
+{
+	return 0;
+}
+
+static void sifive_serial_config_port(struct uart_port *port, int flags)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	ssp->port.type = PORT_SIFIVE_V0;
+}
+
+static int sifive_serial_verify_port(struct uart_port *port,
+				     struct serial_struct *ser)
+{
+	return -EINVAL;
+}
+
+static const char *sifive_serial_type(struct uart_port *port)
+{
+	return port->type == PORT_SIFIVE_V0 ? "SiFive UART v0" : NULL;
+}
+
+/*
+ * Early console support
+ */
+
+#ifdef CONFIG_SERIAL_EARLYCON
+static void early_sifive_serial_putc(struct uart_port *port, int c)
+{
+	while (__ssp_early_readl(port, SIFIVE_SERIAL_TXDATA_OFFS) &
+	       SIFIVE_SERIAL_TXDATA_FULL_MASK)
+		cpu_relax();
+
+	__ssp_early_writel(c, SIFIVE_SERIAL_TXDATA_OFFS, port);
+}
+
+static void early_sifive_serial_write(struct console *con, const char *s,
+				      unsigned int n)
+{
+	struct earlycon_device *dev = con->data;
+	struct uart_port *port = &dev->port;
+
+	uart_console_write(port, s, n, early_sifive_serial_putc);
+}
+
+static int __init early_sifive_serial_setup(struct earlycon_device *dev,
+					    const char *options)
+{
+	struct uart_port *port = &dev->port;
+
+	if (!port->membase)
+		return -ENODEV;
+
+	dev->con->write = early_sifive_serial_write;
+
+	return 0;
+}
+
+OF_EARLYCON_DECLARE(sifive, "sifive,uart0", early_sifive_serial_setup);
+OF_EARLYCON_DECLARE(sifive, "sifive,fu540-c000-uart0",
+		    early_sifive_serial_setup);
+#endif /* CONFIG_SERIAL_EARLYCON */
+
+/*
+ * Linux console interface
+ */
+
+#ifdef CONFIG_SERIAL_SIFIVE_CONSOLE
+
+static struct sifive_serial_port *sifive_serial_console_ports[SIFIVE_SERIAL_MAX_PORTS];
+
+static void sifive_serial_console_putchar(struct uart_port *port, int ch)
+{
+	struct sifive_serial_port *ssp = port_to_sifive_serial_port(port);
+
+	__ssp_wait_for_xmitr(ssp);
+	__ssp_transmit_char(ssp, ch);
+}
+
+static void sifive_serial_console_write(struct console *co, const char *s,
+					unsigned int count)
+{
+	struct sifive_serial_port *ssp = sifive_serial_console_ports[co->index];
+	unsigned long flags;
+	unsigned int ier;
+	int locked = 1;
+
+	if (!ssp)
+		return;
+
+	local_irq_save(flags);
+	if (ssp->port.sysrq)
+		locked = 0;
+	else if (oops_in_progress)
+		locked = spin_trylock(&ssp->port.lock);
+	else
+		spin_lock(&ssp->port.lock);
+
+	ier = __ssp_readl(ssp, SIFIVE_SERIAL_IE_OFFS);
+	__ssp_writel(0, SIFIVE_SERIAL_IE_OFFS, ssp);
+
+	uart_console_write(&ssp->port, s, count, sifive_serial_console_putchar);
+
+	__ssp_writel(ier, SIFIVE_SERIAL_IE_OFFS, ssp);
+
+	if (locked)
+		spin_unlock(&ssp->port.lock);
+	local_irq_restore(flags);
+}
+
+static int __init sifive_serial_console_setup(struct console *co, char *options)
+{
+	struct sifive_serial_port *ssp;
+	int baud = SIFIVE_DEFAULT_BAUD_RATE;
+	int bits = 8;
+	int parity = 'n';
+	int flow = 'n';
+
+	if (co->index < 0 || co->index >= SIFIVE_SERIAL_MAX_PORTS)
+		return -ENODEV;
+
+	ssp = sifive_serial_console_ports[co->index];
+	if (!ssp)
+		return -ENODEV;
+
+	if (options)
+		uart_parse_options(options, &baud, &parity, &bits, &flow);
+
+	return uart_set_options(&ssp->port, co, baud, parity, bits, flow);
+}
+
+static struct uart_driver sifive_serial_uart_driver;
+
+static struct console sifive_serial_console = {
+	.name		= SIFIVE_TTY_PREFIX,
+	.write		= sifive_serial_console_write,
+	.device		= uart_console_device,
+	.setup		= sifive_serial_console_setup,
+	.flags		= CON_PRINTBUFFER,
+	.index		= -1,
+	.data		= &sifive_serial_uart_driver,
+};
+
+static int __init sifive_console_init(void)
+{
+	register_console(&sifive_serial_console);
+	return 0;
+}
+
+console_initcall(sifive_console_init);
+
+static void __ssp_add_console_port(struct sifive_serial_port *ssp)
+{
+	sifive_serial_console_ports[ssp->port.line] = ssp;
+}
+
+static void __ssp_remove_console_port(struct sifive_serial_port *ssp)
+{
+	sifive_serial_console_ports[ssp->port.line] = 0;
+}
+
+#define SIFIVE_SERIAL_CONSOLE	(&sifive_serial_console)
+
+#else
+
+#define SIFIVE_SERIAL_CONSOLE	NULL
+
+static inline void __ssp_add_console_port(struct sifive_serial_port *ssp)
+{}
+static void __ssp_remove_console_port(struct sifive_serial_port *ssp)
+{}
+
+#endif
+
+static const struct uart_ops sifive_serial_uops = {
+	.tx_empty	= sifive_serial_tx_empty,
+	.set_mctrl	= sifive_serial_set_mctrl,
+	.get_mctrl	= sifive_serial_get_mctrl,
+	.stop_tx	= sifive_serial_stop_tx,
+	.start_tx	= sifive_serial_start_tx,
+	.stop_rx	= sifive_serial_stop_rx,
+	.break_ctl	= sifive_serial_break_ctl,
+	.startup	= sifive_serial_startup,
+	.shutdown	= sifive_serial_shutdown,
+	.set_termios	= sifive_serial_set_termios,
+	.type		= sifive_serial_type,
+	.release_port	= sifive_serial_release_port,
+	.request_port	= sifive_serial_request_port,
+	.config_port	= sifive_serial_config_port,
+	.verify_port	= sifive_serial_verify_port,
+};
+
+static struct uart_driver sifive_serial_uart_driver = {
+	.owner		= THIS_MODULE,
+	.driver_name	= SIFIVE_SERIAL_NAME,
+	.dev_name	= SIFIVE_TTY_PREFIX,
+	.nr		= SIFIVE_SERIAL_MAX_PORTS,
+	.cons		= SIFIVE_SERIAL_CONSOLE,
+};
+
+static int sifive_serial_probe(struct platform_device *pdev)
+{
+	struct sifive_serial_port *ssp;
+	struct resource *mem;
+	struct clk *clk;
+	void __iomem *base;
+	int irq, id, r;
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0) {
+		dev_err(&pdev->dev, "could not acquire interrupt\n");
+		return -EPROBE_DEFER;
+	}
+
+	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	base = devm_ioremap_resource(&pdev->dev, mem);
+	if (IS_ERR(base)) {
+		dev_err(&pdev->dev, "could not acquire device memory\n");
+		return PTR_ERR(base);
+	}
+
+	clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(clk)) {
+		dev_err(&pdev->dev, "unable to find controller clock\n");
+		return PTR_ERR(clk);
+	}
+
+	id = of_alias_get_id(pdev->dev.of_node, "serial");
+	if (id < 0) {
+		dev_err(&pdev->dev, "missing aliases entry\n");
+		return id;
+	}
+
+#ifdef CONFIG_SERIAL_SIFIVE_CONSOLE
+	if (id > SIFIVE_SERIAL_MAX_PORTS) {
+		dev_err(&pdev->dev, "too many UARTs (%d)\n", id);
+		return -EINVAL;
+	}
+#endif
+
+	ssp = devm_kzalloc(&pdev->dev, sizeof(*ssp), GFP_KERNEL);
+	if (!ssp)
+		return -ENOMEM;
+
+	ssp->port.dev = &pdev->dev;
+	ssp->port.type = PORT_SIFIVE_V0;
+	ssp->port.iotype = UPIO_MEM;
+	ssp->port.irq = irq;
+	ssp->port.fifosize = SIFIVE_TX_FIFO_DEPTH;
+	ssp->port.ops = &sifive_serial_uops;
+	ssp->port.line = id;
+	ssp->port.mapbase = mem->start;
+	ssp->port.membase = base;
+	ssp->dev = &pdev->dev;
+	ssp->clk = clk;
+	ssp->clk_notifier.notifier_call = sifive_serial_clk_notifier;
+
+	r = clk_notifier_register(ssp->clk, &ssp->clk_notifier);
+	if (r) {
+		dev_err(&pdev->dev, "could not register clock notifier: %d\n",
+			r);
+		goto probe_out1;
+	}
+
+	/* Set up clock divider */
+	ssp->clkin_rate = clk_get_rate(ssp->clk);
+	ssp->baud_rate = SIFIVE_DEFAULT_BAUD_RATE;
+	__ssp_update_div(ssp);
+
+	platform_set_drvdata(pdev, ssp);
+
+	/* Enable transmits and set the watermark level to 1 */
+	__ssp_writel((1 << SIFIVE_SERIAL_TXCTRL_TXCNT_SHIFT) |
+		     SIFIVE_SERIAL_TXCTRL_TXEN_MASK,
+		     SIFIVE_SERIAL_TXCTRL_OFFS, ssp);
+
+	/* Enable receives and set the watermark level to 0 */
+	__ssp_writel((0 << SIFIVE_SERIAL_RXCTRL_RXCNT_SHIFT) |
+		     SIFIVE_SERIAL_RXCTRL_RXEN_MASK,
+		     SIFIVE_SERIAL_RXCTRL_OFFS, ssp);
+
+	r = request_irq(ssp->port.irq, sifive_serial_irq, ssp->port.irqflags,
+			dev_name(&pdev->dev), ssp);
+	if (r) {
+		dev_err(&pdev->dev, "could not attach interrupt: %d\n", r);
+		goto probe_out2;
+	}
+
+	__ssp_add_console_port(ssp);
+
+	r = uart_add_one_port(&sifive_serial_uart_driver, &ssp->port);
+	if (r != 0) {
+		dev_err(&pdev->dev, "could not add uart: %d\n", r);
+		goto probe_out3;
+	}
+
+	return 0;
+
+probe_out3:
+	__ssp_remove_console_port(ssp);
+	free_irq(ssp->port.irq, ssp);
+probe_out2:
+	clk_notifier_unregister(ssp->clk, &ssp->clk_notifier);
+probe_out1:
+	return r;
+}
+
+static int sifive_serial_remove(struct platform_device *dev)
+{
+	struct sifive_serial_port *ssp = platform_get_drvdata(dev);
+
+	__ssp_remove_console_port(ssp);
+	uart_remove_one_port(&sifive_serial_uart_driver, &ssp->port);
+	free_irq(ssp->port.irq, ssp);
+	clk_notifier_unregister(ssp->clk, &ssp->clk_notifier);
+
+	return 0;
+}
+
+static const struct of_device_id sifive_serial_of_match[] = {
+	{ .compatible = "sifive,fu540-c000-uart0" },
+	{ .compatible = "sifive,uart0" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, sifive_serial_of_match);
+
+static struct platform_driver sifive_serial_platform_driver = {
+	.probe		= sifive_serial_probe,
+	.remove		= sifive_serial_remove,
+	.driver		= {
+		.name	= SIFIVE_SERIAL_NAME,
+		.of_match_table = of_match_ptr(sifive_serial_of_match),
+	},
+};
+
+static int __init sifive_serial_init(void)
+{
+	int r;
+
+	r = uart_register_driver(&sifive_serial_uart_driver);
+	if (r)
+		goto init_out1;
+
+	r = platform_driver_register(&sifive_serial_platform_driver);
+	if (r)
+		goto init_out2;
+
+	return 0;
+
+init_out2:
+	uart_unregister_driver(&sifive_serial_uart_driver);
+init_out1:
+	return r;
+}
+
+static void __exit sifive_serial_exit(void)
+{
+	platform_driver_unregister(&sifive_serial_platform_driver);
+	uart_unregister_driver(&sifive_serial_uart_driver);
+}
+
+module_init(sifive_serial_init);
+module_exit(sifive_serial_exit);
+
+MODULE_DESCRIPTION("SiFive UART serial driver");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Paul Walmsley <paul@pwsan.com>");
diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h
index dce5f9dae121..569d5172d23c 100644
--- a/include/uapi/linux/serial_core.h
+++ b/include/uapi/linux/serial_core.h
@@ -281,4 +281,7 @@
 /* MediaTek BTIF */
 #define PORT_MTK_BTIF	117
 
+/* SiFive UART */
+#define PORT_SIFIVE_V0	118
+
 #endif /* _UAPILINUX_SERIAL_CORE_H */
-- 
2.19.1


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[PATCH v3 2/2] tty: serial: add driver for the SiFive UART

[Emil Renner Berthing]

Hi Paul,

Thanks for the patch!

On Sat, 20 Oct 2018 at 12:12, Paul Walmsley <paul.walmsley@sifive.com> wrote:
> +/*
> + *
> + */

Interesting comment ;)

> +static int __init sifive_serial_console_setup(struct console *co, char *options)

Unfortunately I get this error unless I remove the __init:
...
  GEN     .version
  CHK     include/generated/compile.h
  AR      built-in.a
  LD      vmlinux.o
  MODPOST vmlinux.o
WARNING: vmlinux.o(.data+0x14e48): Section mismatch in reference from
the variable .LANCHOR0 to the function
.init.text:sifive_serial_console_setup()
The variable .LANCHOR0 references
the function __init sifive_serial_console_setup()
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

FATAL: modpost: Section mismatches detected.
Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.
make[1]: *** [scripts/Makefile.modpost:98: vmlinux.o] Error 1
make: *** [Makefile:1040: vmlinux] Error 2

I have
CONFIG_SERIAL_CORE=y
CONFIG_SERIAL_CORE_CONSOLE=y
CONFIG_SERIAL_SIFIVE=y
CONFIG_SERIAL_SIFIVE_CONSOLE=y
and it happens both on v4.20-rc2 and v4.19.
Without the __init everything seems to work fine though.

> +#else
> +
> +#define SIFIVE_SERIAL_CONSOLE  NULL
> +
> +static inline void __ssp_add_console_port(struct sifive_serial_port *ssp)
> +{}
> +static void __ssp_remove_console_port(struct sifive_serial_port *ssp)
> +{}

Missing "inline"?

> +static int __init sifive_serial_init(void)
> +{
> +       int r;

If you're sending a v4 anyway, here and in the the probe function
using int ret; for this kind of variable is a common idiom and
hence easier to read.

/Emil

Re: [PATCH v3 2/2] tty: serial: add driver for the SiFive UART

[Emil Renner Berthing]

Hi Paul,

Thanks for the patch!

On Sat, 20 Oct 2018 at 12:12, Paul Walmsley <paul.walmsley@sifive.com> wrote:
> +/*
> + *
> + */

Interesting comment ;)

> +static int __init sifive_serial_console_setup(struct console *co, char *options)

Unfortunately I get this error unless I remove the __init:
...
  GEN     .version
  CHK     include/generated/compile.h
  AR      built-in.a
  LD      vmlinux.o
  MODPOST vmlinux.o
WARNING: vmlinux.o(.data+0x14e48): Section mismatch in reference from
the variable .LANCHOR0 to the function
.init.text:sifive_serial_console_setup()
The variable .LANCHOR0 references
the function __init sifive_serial_console_setup()
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

FATAL: modpost: Section mismatches detected.
Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.
make[1]: *** [scripts/Makefile.modpost:98: vmlinux.o] Error 1
make: *** [Makefile:1040: vmlinux] Error 2

I have
CONFIG_SERIAL_CORE=y
CONFIG_SERIAL_CORE_CONSOLE=y
CONFIG_SERIAL_SIFIVE=y
CONFIG_SERIAL_SIFIVE_CONSOLE=y
and it happens both on v4.20-rc2 and v4.19.
Without the __init everything seems to work fine though.

> +#else
> +
> +#define SIFIVE_SERIAL_CONSOLE  NULL
> +
> +static inline void __ssp_add_console_port(struct sifive_serial_port *ssp)
> +{}
> +static void __ssp_remove_console_port(struct sifive_serial_port *ssp)
> +{}

Missing "inline"?

> +static int __init sifive_serial_init(void)
> +{
> +       int r;

If you're sending a v4 anyway, here and in the the probe function
using int ret; for this kind of variable is a common idiom and
hence easier to read.

/Emil

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[PATCH v3 2/2] tty: serial: add driver for the SiFive UART

[Paul Walmsley]

Hi Emil,

On Thu, 15 Nov 2018, Emil Renner Berthing wrote:

> Thanks for the patch!

Thanks for your comments!

> On Sat, 20 Oct 2018 at 12:12, Paul Walmsley <paul.walmsley@sifive.com> wrote:
>
>> +static int __init sifive_serial_console_setup(struct console *co, char *options)
>
> Unfortunately I get this error unless I remove the __init:
> ...
>  GEN     .version
>  CHK     include/generated/compile.h
>  AR      built-in.a
>  LD      vmlinux.o
>  MODPOST vmlinux.o
> WARNING: vmlinux.o(.data+0x14e48): Section mismatch in reference from
> the variable .LANCHOR0 to the function
> .init.text:sifive_serial_console_setup()
> The variable .LANCHOR0 references
> the function __init sifive_serial_console_setup()
> If the reference is valid then annotate the
> variable with __init* or __refdata (see linux/init.h) or name the variable:
> *_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console
>
> FATAL: modpost: Section mismatches detected.
> Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.
> make[1]: *** [scripts/Makefile.modpost:98: vmlinux.o] Error 1
> make: *** [Makefile:1040: vmlinux] Error 2
>
> I have
> CONFIG_SERIAL_CORE=y
> CONFIG_SERIAL_CORE_CONSOLE=y
> CONFIG_SERIAL_SIFIVE=y
> CONFIG_SERIAL_SIFIVE_CONSOLE=y
> and it happens both on v4.20-rc2 and v4.19.
> Without the __init everything seems to work fine though.

Thanks for the report.  There are some patches to address this:

https://lore.kernel.org/lkml/20181115005602.30746-1-paul.walmsley at sifive.com/

>> +#else
>> +
>> +#define SIFIVE_SERIAL_CONSOLE  NULL
>> +
>> +static inline void __ssp_add_console_port(struct sifive_serial_port *ssp)
>> +{}
>> +static void __ssp_remove_console_port(struct sifive_serial_port *ssp)
>> +{}
>
> Missing "inline"?

That is indeed an error, but the other way around: I didn't mean for that 
inline to be there.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst

I've dropped the inline; thanks for pointing the situation out.

>> +static int __init sifive_serial_init(void)
>> +{
>> +       int r;
>
> If you're sending a v4 anyway, here and in the the probe function
> using int ret; for this kind of variable is a common idiom and
> hence easier to read.

Precedent exists in the kernel for using "r" as a return value also:

$ fgrep -r 'return r;' linux/
4491
$

which probably traces back ultimately to Torvalds' guidance to keep 
variable names short:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst#n284

But I am not religious about it.   So if this is a big deal for you, I 
guess reply back, and it can be changed.


- Paul

Re: [PATCH v3 2/2] tty: serial: add driver for the SiFive UART

[Paul Walmsley]

Hi Emil,

On Thu, 15 Nov 2018, Emil Renner Berthing wrote:

> Thanks for the patch!

Thanks for your comments!

> On Sat, 20 Oct 2018 at 12:12, Paul Walmsley <paul.walmsley@sifive.com> wrote:
>
>> +static int __init sifive_serial_console_setup(struct console *co, char *options)
>
> Unfortunately I get this error unless I remove the __init:
> ...
>  GEN     .version
>  CHK     include/generated/compile.h
>  AR      built-in.a
>  LD      vmlinux.o
>  MODPOST vmlinux.o
> WARNING: vmlinux.o(.data+0x14e48): Section mismatch in reference from
> the variable .LANCHOR0 to the function
> .init.text:sifive_serial_console_setup()
> The variable .LANCHOR0 references
> the function __init sifive_serial_console_setup()
> If the reference is valid then annotate the
> variable with __init* or __refdata (see linux/init.h) or name the variable:
> *_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console
>
> FATAL: modpost: Section mismatches detected.
> Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.
> make[1]: *** [scripts/Makefile.modpost:98: vmlinux.o] Error 1
> make: *** [Makefile:1040: vmlinux] Error 2
>
> I have
> CONFIG_SERIAL_CORE=y
> CONFIG_SERIAL_CORE_CONSOLE=y
> CONFIG_SERIAL_SIFIVE=y
> CONFIG_SERIAL_SIFIVE_CONSOLE=y
> and it happens both on v4.20-rc2 and v4.19.
> Without the __init everything seems to work fine though.

Thanks for the report.  There are some patches to address this:

https://lore.kernel.org/lkml/20181115005602.30746-1-paul.walmsley@sifive.com/

>> +#else
>> +
>> +#define SIFIVE_SERIAL_CONSOLE  NULL
>> +
>> +static inline void __ssp_add_console_port(struct sifive_serial_port *ssp)
>> +{}
>> +static void __ssp_remove_console_port(struct sifive_serial_port *ssp)
>> +{}
>
> Missing "inline"?

That is indeed an error, but the other way around: I didn't mean for that 
inline to be there.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst

I've dropped the inline; thanks for pointing the situation out.

>> +static int __init sifive_serial_init(void)
>> +{
>> +       int r;
>
> If you're sending a v4 anyway, here and in the the probe function
> using int ret; for this kind of variable is a common idiom and
> hence easier to read.

Precedent exists in the kernel for using "r" as a return value also:

$ fgrep -r 'return r;' linux/
4491
$

which probably traces back ultimately to Torvalds' guidance to keep 
variable names short:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst#n284

But I am not religious about it.   So if this is a big deal for you, I 
guess reply back, and it can be changed.


- Paul


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Re: [PATCH v3 0/2] tty: serial: add DT bindings and serial driver for the SiFive FU540 UART

[Andreas Schwab]

Trying to log in on the serial console causes the system to freeze.  The
last message is:

[  115.597858] sifive-serial 10010000.serial: BRKINT/PARMRK flag not supported

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

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Re: [PATCH v3 0/2] tty: serial: add DT bindings and serial driver for the SiFive FU540 UART

[Paul Walmsley]

On Wed, 6 Mar 2019, Andreas Schwab wrote:

> Trying to log in on the serial console causes the system to freeze.  The
> last message is:
> 
> [  115.597858] sifive-serial 10010000.serial: BRKINT/PARMRK flag not supported

Have not seen that problem.

If you're still seeing this, could you follow up with me off-list so we 
can synchronize configurations, both with the kernel and with non-kernel 
boot & M-mode components?


- Paul

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Re: [PATCH v3 0/2] tty: serial: add DT bindings and serial driver for the SiFive FU540 UART

[Andreas Schwab]

On Apr 11 2019, Paul Walmsley <paul.walmsley@sifive.com> wrote:

> On Wed, 6 Mar 2019, Andreas Schwab wrote:
>
>> Trying to log in on the serial console causes the system to freeze.  The
>> last message is:
>> 
>> [  115.597858] sifive-serial 10010000.serial: BRKINT/PARMRK flag not supported
>
> Have not seen that problem.

# stty sane -F /dev/ttySIF0
<crash>

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

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