[PATCH v6 0/2] Add UART driver for Suplus SP7021 SoC

[PATCH v6 0/2] Add UART driver for Suplus SP7021 SoC

[Hammer Hsieh]

This is a patch series for UART driver for Suplus SP7021 SoC.

Sunplus SP7021 is an ARM Cortex A7 (4 cores) based SoC. It integrates
many peripherals (ex: UART. I2C, SPI, SDIO, eMMC, USB, SD card and
etc.) into a single chip. It is designed for industrial control.

Refer to:
https://sunplus-tibbo.atlassian.net/wiki/spaces/doc/overview
https://tibbo.com/store/plus1.html

Refer to (UART):
https://sunplus.atlassian.net/wiki/spaces/doc/pages/1873412290/13.+Universal+Asynchronous+Receiver+Transmitter+UART

Hammer Hsieh (2):
  dt-bindings:serial:Add bindings doc for Sunplus SoC UART Driver
  serial:sunplus-uart:Add Sunplus SoC UART Driver

 .../bindings/serial/sunplus,sp7021-uart.yaml       |  56 ++
 MAINTAINERS                                        |   6 +
 drivers/tty/serial/Kconfig                         |  25 +
 drivers/tty/serial/Makefile                        |   1 +
 drivers/tty/serial/sunplus-uart.c                  | 756 +++++++++++++++++++++
 include/uapi/linux/serial_core.h                   |   3 +
 6 files changed, 847 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/serial/sunplus,sp7021-uart.yaml
 create mode 100644 drivers/tty/serial/sunplus-uart.c

-- 
2.7.4

[PATCH v6 1/2] dt-bindings:serial:Add bindings doc for Sunplus SoC UART Driver

[Hammer Hsieh]

Add bindings doc for Sunplus SoC UART Driver

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hammer Hsieh <hammerh0314@gmail.com>
---
Changes in v6:
 - modify author mail match Signed-off-by.

 .../bindings/serial/sunplus,sp7021-uart.yaml       | 56 ++++++++++++++++++++++
 MAINTAINERS                                        |  5 ++
 2 files changed, 61 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/serial/sunplus,sp7021-uart.yaml

diff --git a/Documentation/devicetree/bindings/serial/sunplus,sp7021-uart.yaml b/Documentation/devicetree/bindings/serial/sunplus,sp7021-uart.yaml
new file mode 100644
index 0000000..894324c
--- /dev/null
+++ b/Documentation/devicetree/bindings/serial/sunplus,sp7021-uart.yaml
@@ -0,0 +1,56 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+# Copyright (C) Sunplus Co., Ltd. 2021
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/serial/sunplus,sp7021-uart.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Sunplus SoC SP7021 UART Controller Device Tree Bindings
+
+maintainers:
+  - Hammer Hsieh <hammerh0314@gmail.com>
+
+allOf:
+  - $ref: serial.yaml#
+
+properties:
+  compatible:
+    const: sunplus,sp7021-uart
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  resets:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+  - resets
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    aliases {
+            serial0 = &uart0;
+    };
+
+    uart0: serial@9c000900 {
+        compatible = "sunplus,sp7021-uart";
+        reg = <0x9c000900 0x80>;
+        interrupt-parent = <&intc>;
+        interrupts = <53 IRQ_TYPE_LEVEL_HIGH>;
+        clocks = <&clkc 0x28>;
+        resets = <&rstc 0x18>;
+    };
+...
diff --git a/MAINTAINERS b/MAINTAINERS
index 3b79fd4..3c1362e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17945,6 +17945,11 @@ L:	netdev@vger.kernel.org
 S:	Maintained
 F:	drivers/net/ethernet/dlink/sundance.c
 
+SUNPLUS UART DRIVER
+M:	Hammer Hsieh <hammerh0314@gmail.com>
+S:	Maintained
+F:	Documentation/devicetree/bindings/serial/sunplus,sp7021-uart.yaml
+
 SUPERH
 M:	Yoshinori Sato <ysato@users.sourceforge.jp>
 M:	Rich Felker <dalias@libc.org>
-- 
2.7.4

[PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

[Hammer Hsieh]

Add Sunplus SoC UART Driver

Signed-off-by: Hammer Hsieh <hammerh0314@gmail.com>
---
Changes in v6:
 - Addressed all comments from Jiri Slaby and Greg KH.

 MAINTAINERS                       |   1 +
 drivers/tty/serial/Kconfig        |  25 ++
 drivers/tty/serial/Makefile       |   1 +
 drivers/tty/serial/sunplus-uart.c | 756 ++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/serial_core.h  |   3 +
 5 files changed, 786 insertions(+)
 create mode 100644 drivers/tty/serial/sunplus-uart.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 3c1362e..2dc2fe6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17949,6 +17949,7 @@ SUNPLUS UART DRIVER
 M:	Hammer Hsieh <hammerh0314@gmail.com>
 S:	Maintained
 F:	Documentation/devicetree/bindings/serial/sunplus,sp7021-uart.yaml
+F:	drivers/tty/serial/sunplus-uart.c
 
 SUPERH
 M:	Yoshinori Sato <ysato@users.sourceforge.jp>
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 131a6a5..0865da3 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1561,6 +1561,31 @@ config SERIAL_LITEUART_CONSOLE
 	  and warnings and which allows logins in single user mode).
 	  Otherwise, say 'N'.
 
+config SERIAL_SUNPLUS
+	tristate "Sunplus UART support"
+	depends on OF || COMPILE_TEST
+	select SERIAL_CORE
+	help
+	  Select this option if you would like to use Sunplus serial port on
+	  Sunplus SoC SP7021.
+	  If you enable this option, Sunplus serial ports in the system will
+	  be registered as ttySUPx.
+	  This driver can also be built as a module. If so, the module will be
+	  called sunplus-uart.
+
+config SERIAL_SUNPLUS_CONSOLE
+	bool "Console on Sunplus UART"
+	depends on SERIAL_SUNPLUS
+	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON
+	help
+	  Select this option if you would like to use a Sunplus 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=ttySUPx".
+
 endmenu
 
 config SERIAL_MCTRL_GPIO
diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index 7da0856..61cc8de 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile
@@ -87,6 +87,7 @@ obj-$(CONFIG_SERIAL_RDA)	+= rda-uart.o
 obj-$(CONFIG_SERIAL_MILBEAUT_USIO) += milbeaut_usio.o
 obj-$(CONFIG_SERIAL_SIFIVE)	+= sifive.o
 obj-$(CONFIG_SERIAL_LITEUART) += liteuart.o
+obj-$(CONFIG_SERIAL_SUNPLUS)	+= sunplus-uart.o
 
 # GPIOLIB helpers for modem control lines
 obj-$(CONFIG_SERIAL_MCTRL_GPIO)	+= serial_mctrl_gpio.o
diff --git a/drivers/tty/serial/sunplus-uart.c b/drivers/tty/serial/sunplus-uart.c
new file mode 100644
index 0000000..8b7306d
--- /dev/null
+++ b/drivers/tty/serial/sunplus-uart.c
@@ -0,0 +1,756 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Sunplus SoC UART driver
+ *
+ * Author: Hammer Hsieh <hammerh0314@gmail.com>
+ */
+#include <linux/clk.h>
+#include <linux/console.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/reset.h>
+#include <linux/serial_core.h>
+#include <linux/serial_reg.h>
+#include <linux/sysrq.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <asm/irq.h>
+
+/* Register offsets */
+#define SUP_UART_DATA			0x00
+#define SUP_UART_LSR			0x04
+#define SUP_UART_MSR			0x08
+#define SUP_UART_LCR			0x0C
+#define SUP_UART_MCR			0x10
+#define SUP_UART_DIV_L			0x14
+#define SUP_UART_DIV_H			0x18
+#define SUP_UART_ISC			0x1C
+#define SUP_UART_TX_RESIDUE		0x20
+#define SUP_UART_RX_RESIDUE		0x24
+
+/* Line Status Register bits */
+#define SUP_UART_LSR_BC			BIT(5) /* break condition status */
+#define SUP_UART_LSR_FE			BIT(4) /* frame error status */
+#define SUP_UART_LSR_OE			BIT(3) /* overrun error status */
+#define SUP_UART_LSR_PE			BIT(2) /* parity error status */
+#define SUP_UART_LSR_RX			BIT(1) /* 1: receive fifo not empty */
+#define SUP_UART_LSR_TX			BIT(0) /* 1: transmit fifo is not full */
+#define SUP_UART_LSR_TX_NOT_FULL	1
+#define SUP_UART_LSR_BRK_ERROR_BITS	GENMASK(5, 2)
+
+/* Line Control Register bits */
+#define SUP_UART_LCR_SBC		BIT(5) /* select break condition */
+
+/* Modem Control Register bits */
+#define SUP_UART_MCR_RI			BIT(3) /* ring indicator */
+#define SUP_UART_MCR_DCD		BIT(2) /* data carrier detect */
+
+/* Interrupt Status/Control Register bits */
+#define SUP_UART_ISC_RXM		BIT(5) /* RX interrupt enable */
+#define SUP_UART_ISC_TXM		BIT(4) /* TX interrupt enable */
+#define SUP_UART_ISC_RX			BIT(1) /* RX interrupt status */
+#define SUP_UART_ISC_TX			BIT(0) /* TX interrupt status */
+
+#define SUP_DUMMY_READ			BIT(16) /* drop bytes received on a !CREAD port */
+#define SUP_UART_NR			5
+
+struct sunplus_uart_port {
+	struct uart_port port;
+	struct clk *clk;
+	struct reset_control *rstc;
+};
+
+static void sp_uart_put_char(struct uart_port *port, unsigned int ch)
+{
+	writel(ch, port->membase + SUP_UART_DATA);
+}
+
+static u32 sunplus_tx_buf_not_full(struct uart_port *port)
+{
+	unsigned int lsr = readl(port->membase + SUP_UART_LSR);
+
+	return (lsr & SUP_UART_LSR_TX) ? SUP_UART_LSR_TX_NOT_FULL : 0;
+}
+
+static unsigned int sunplus_tx_empty(struct uart_port *port)
+{
+	unsigned int lsr = readl(port->membase + SUP_UART_LSR);
+
+	return (lsr & UART_LSR_TEMT) ? TIOCSER_TEMT : 0;
+}
+
+static void sunplus_set_mctrl(struct uart_port *port, unsigned int mctrl)
+{
+	unsigned int mcr = readl(port->membase + SUP_UART_MCR);
+
+	if (mctrl & TIOCM_DTR)
+		mcr |= UART_MCR_DTR;
+	else
+		mcr &= ~UART_MCR_DTR;
+
+	if (mctrl & TIOCM_RTS)
+		mcr |= UART_MCR_RTS;
+	else
+		mcr &= ~UART_MCR_RTS;
+
+	if (mctrl & TIOCM_CAR)
+		mcr |= SUP_UART_MCR_DCD;
+	else
+		mcr &= ~SUP_UART_MCR_DCD;
+
+	if (mctrl & TIOCM_RI)
+		mcr |= SUP_UART_MCR_RI;
+	else
+		mcr &= ~SUP_UART_MCR_RI;
+
+	if (mctrl & TIOCM_LOOP)
+		mcr |= UART_MCR_LOOP;
+	else
+		mcr &= ~UART_MCR_LOOP;
+
+	writel(mcr, port->membase + SUP_UART_MCR);
+}
+
+static unsigned int sunplus_get_mctrl(struct uart_port *port)
+{
+	unsigned int ret, mcr;
+
+	mcr = readl(port->membase + SUP_UART_MCR);
+
+	if (mcr & UART_MCR_DTR)
+		ret |= TIOCM_DTR;
+
+	if (mcr & UART_MCR_RTS)
+		ret |= TIOCM_RTS;
+
+	if (mcr & SUP_UART_MCR_DCD)
+		ret |= TIOCM_CAR;
+
+	if (mcr & SUP_UART_MCR_RI)
+		ret |= TIOCM_RI;
+
+	if (mcr & UART_MCR_LOOP)
+		ret |= TIOCM_LOOP;
+
+	return ret;
+}
+
+static void sunplus_stop_tx(struct uart_port *port)
+{
+	unsigned int isc;
+
+	isc = readl(port->membase + SUP_UART_ISC);
+	isc &= ~SUP_UART_ISC_TXM;
+	writel(isc, port->membase + SUP_UART_ISC);
+}
+
+static void sunplus_start_tx(struct uart_port *port)
+{
+	unsigned int isc;
+
+	isc = readl(port->membase + SUP_UART_ISC);
+	isc |= SUP_UART_ISC_TXM;
+	writel(isc, port->membase + SUP_UART_ISC);
+}
+
+static void sunplus_stop_rx(struct uart_port *port)
+{
+	unsigned int isc;
+
+	isc = readl(port->membase + SUP_UART_ISC);
+	isc &= ~SUP_UART_ISC_RXM;
+	writel(isc, port->membase + SUP_UART_ISC);
+}
+
+static void sunplus_break_ctl(struct uart_port *port, int ctl)
+{
+	unsigned long flags;
+	unsigned int lcr;
+
+	spin_lock_irqsave(&port->lock, flags);
+
+	lcr = readl(port->membase + SUP_UART_LCR);
+
+	if (ctl)
+		lcr |= SUP_UART_LCR_SBC; /* start break */
+	else
+		lcr &= ~SUP_UART_LCR_SBC; /* stop break */
+
+	writel(lcr, port->membase + SUP_UART_LCR);
+
+	spin_unlock_irqrestore(&port->lock, flags);
+}
+
+static void transmit_chars(struct uart_port *port)
+{
+	struct circ_buf *xmit = &port->state->xmit;
+
+	if (port->x_char) {
+		sp_uart_put_char(port, port->x_char);
+		port->icount.tx++;
+		port->x_char = 0;
+		return;
+	}
+
+	if (uart_circ_empty(xmit) || uart_tx_stopped(port)) {
+		sunplus_stop_tx(port);
+		return;
+	}
+
+	do {
+		sp_uart_put_char(port, xmit->buf[xmit->tail]);
+		xmit->tail = (xmit->tail + 1) % UART_XMIT_SIZE;
+		port->icount.tx++;
+
+		if (uart_circ_empty(xmit))
+			break;
+	} while (sunplus_tx_buf_not_full(port));
+
+	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
+		uart_write_wakeup(port);
+
+	if (uart_circ_empty(xmit))
+		sunplus_stop_tx(port);
+}
+
+static void receive_chars(struct uart_port *port)
+{
+	unsigned int lsr = readl(port->membase + SUP_UART_LSR);
+	unsigned int ch, flag;
+
+	do {
+		ch = readl(port->membase + SUP_UART_DATA);
+		flag = TTY_NORMAL;
+		port->icount.rx++;
+
+		if (unlikely(lsr & SUP_UART_LSR_BRK_ERROR_BITS)) {
+			if (lsr & SUP_UART_LSR_BC) {
+				lsr &= ~(SUP_UART_LSR_FE | SUP_UART_LSR_PE);
+				port->icount.brk++;
+				flag = TTY_BREAK;
+				if (uart_handle_break(port))
+					goto ignore_char;
+			} else if (lsr & SUP_UART_LSR_PE) {
+				port->icount.parity++;
+				flag = TTY_PARITY;
+			} else if (lsr & SUP_UART_LSR_FE) {
+				port->icount.frame++;
+				flag = TTY_FRAME;
+			}
+
+			if (lsr & SUP_UART_LSR_OE)
+				port->icount.overrun++;
+		}
+
+		if (port->ignore_status_mask & SUP_DUMMY_READ)
+			goto ignore_char;
+
+		if (uart_handle_sysrq_char(port, ch))
+			goto ignore_char;
+
+		uart_insert_char(port, lsr, SUP_UART_LSR_OE, ch, flag);
+
+ignore_char:
+		lsr = readl(port->membase + SUP_UART_LSR);
+	} while (lsr & SUP_UART_LSR_RX);
+
+	tty_flip_buffer_push(&port->state->port);
+}
+
+static irqreturn_t sunplus_uart_irq(int irq, void *args)
+{
+	struct uart_port *port = args;
+	unsigned int isc;
+
+	spin_lock(&port->lock);
+
+	isc = readl(port->membase + SUP_UART_ISC);
+
+	if (isc & SUP_UART_ISC_RX)
+		receive_chars(port);
+
+	if (isc & SUP_UART_ISC_TX)
+		transmit_chars(port);
+
+	spin_unlock(&port->lock);
+
+	return IRQ_HANDLED;
+}
+
+static int sunplus_startup(struct uart_port *port)
+{
+	unsigned long flags;
+	unsigned int isc;
+	int ret;
+
+	ret = request_irq(port->irq, sunplus_uart_irq, 0, "sunplus_uart", port);
+	if (ret)
+		return ret;
+
+	spin_lock_irqsave(&port->lock, flags);
+
+	isc |= SUP_UART_ISC_RXM;
+	writel(isc, port->membase + SUP_UART_ISC);
+
+	spin_unlock_irqrestore(&port->lock, flags);
+
+	return 0;
+}
+
+static void sunplus_shutdown(struct uart_port *port)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&port->lock, flags);
+	writel(0, port->membase + SUP_UART_ISC);
+	spin_unlock_irqrestore(&port->lock, flags);
+
+	free_irq(port->irq, port);
+}
+
+static void sunplus_set_termios(struct uart_port *port,
+				struct ktermios *termios,
+				struct ktermios *oldtermios)
+{
+	u32 ext, div, div_l, div_h, baud, lcr;
+	u32 clk = port->uartclk;
+	unsigned long flags;
+
+	baud = uart_get_baud_rate(port, termios, oldtermios, 0, port->uartclk / 16);
+
+	/* baud rate = uartclk / ((16 * divisor + 1) + divisor_ext) */
+	clk += baud >> 1;
+	div = clk / baud;
+	ext = div & 0x0F;
+	div = (div >> 4) - 1;
+	div_l = (div & 0xFF) | (ext << 12);
+	div_h = div >> 8;
+
+	switch (termios->c_cflag & CSIZE) {
+	case CS5:
+		lcr = UART_LCR_WLEN5;
+		break;
+	case CS6:
+		lcr = UART_LCR_WLEN6;
+		break;
+	case CS7:
+		lcr = UART_LCR_WLEN7;
+		break;
+	default:
+		lcr = UART_LCR_WLEN8;
+		break;
+	}
+
+	if (termios->c_cflag & CSTOPB)
+		lcr |= UART_LCR_STOP;
+
+	if (termios->c_cflag & PARENB) {
+		lcr |= UART_LCR_PARITY;
+
+		if (!(termios->c_cflag & PARODD))
+			lcr |= UART_LCR_EPAR;
+	}
+
+	spin_lock_irqsave(&port->lock, flags);
+
+	uart_update_timeout(port, termios->c_cflag, baud);
+
+	port->read_status_mask = 0;
+	if (termios->c_iflag & INPCK)
+		port->read_status_mask |= SUP_UART_LSR_PE | SUP_UART_LSR_FE;
+
+	if (termios->c_iflag & (BRKINT | PARMRK))
+		port->read_status_mask |= SUP_UART_LSR_BC;
+
+	/* Characters to ignore */
+	port->ignore_status_mask = 0;
+	if (termios->c_iflag & IGNPAR)
+		port->ignore_status_mask |= SUP_UART_LSR_FE | SUP_UART_LSR_PE;
+
+	if (termios->c_iflag & IGNBRK) {
+		port->ignore_status_mask |= SUP_UART_LSR_BC;
+
+		if (termios->c_iflag & IGNPAR)
+			port->ignore_status_mask |= SUP_UART_LSR_OE;
+	}
+
+	/* Ignore all characters if CREAD is not set */
+	if ((termios->c_cflag & CREAD) == 0) {
+		port->ignore_status_mask |= SUP_DUMMY_READ;
+		/* flush rx data FIFO */
+		writel(0, port->membase + SUP_UART_RX_RESIDUE);
+	}
+
+	/* Settings for baud rate divisor and lcr */
+	writel(div_h, port->membase + SUP_UART_DIV_H);
+	writel(div_l, port->membase + SUP_UART_DIV_L);
+	writel(lcr, port->membase + SUP_UART_LCR);
+
+	spin_unlock_irqrestore(&port->lock, flags);
+}
+
+static void sunplus_set_ldisc(struct uart_port *port, struct ktermios *termios)
+{
+	int new = termios->c_line;
+
+	if (new == N_PPS)
+		port->flags |= UPF_HARDPPS_CD;
+	else
+		port->flags &= ~UPF_HARDPPS_CD;
+}
+
+static const char *sunplus_type(struct uart_port *port)
+{
+	return port->type == PORT_SUNPLUS ? "sunplus_uart" : NULL;
+}
+
+static void sunplus_config_port(struct uart_port *port, int type)
+{
+	if (type & UART_CONFIG_TYPE)
+		port->type = PORT_SUNPLUS;
+}
+
+static int sunplus_verify_port(struct uart_port *port, struct serial_struct *ser)
+{
+	if (ser->type != PORT_UNKNOWN && ser->type != PORT_SUNPLUS)
+		return -EINVAL;
+
+	return 0;
+}
+
+#ifdef CONFIG_CONSOLE_POLL
+static void sunplus_poll_put_char(struct uart_port *port, unsigned char data)
+{
+	wait_for_xmitr(port);
+	sp_uart_put_char(port, data);
+}
+
+static int sunplus_poll_get_char(struct uart_port *port)
+{
+	unsigned int lsr = readl(port->membase + SUP_UART_LSR);
+
+	if (!(lsr & SUP_UART_LSR_RX))
+		return NO_POLL_CHAR;
+
+	return readl(port->membase + SUP_UART_DATA);
+}
+#endif
+
+static const struct uart_ops sunplus_uart_ops = {
+	.tx_empty	= sunplus_tx_empty,
+	.set_mctrl	= sunplus_set_mctrl,
+	.get_mctrl	= sunplus_get_mctrl,
+	.stop_tx	= sunplus_stop_tx,
+	.start_tx	= sunplus_start_tx,
+	.stop_rx	= sunplus_stop_rx,
+	.break_ctl	= sunplus_break_ctl,
+	.startup	= sunplus_startup,
+	.shutdown	= sunplus_shutdown,
+	.set_termios	= sunplus_set_termios,
+	.set_ldisc	= sunplus_set_ldisc,
+	.type		= sunplus_type,
+	.config_port	= sunplus_config_port,
+	.verify_port	= sunplus_verify_port,
+#ifdef CONFIG_CONSOLE_POLL
+	.poll_put_char	= sunplus_poll_put_char,
+	.poll_get_char	= sunplus_poll_get_char,
+#endif
+};
+
+#ifdef CONFIG_SERIAL_SUNPLUS_CONSOLE
+struct sunplus_uart_port *sunplus_console_ports[SUP_UART_NR];
+
+static void wait_for_xmitr(struct uart_port *port)
+{
+	unsigned int val;
+	int ret;
+
+	/* Wait while FIFO is full or timeout */
+	ret = readl_poll_timeout_atomic(port->membase + SUP_UART_LSR, val,
+					(val & SUP_UART_LSR_TX), 1, 10000);
+
+	if (ret == -ETIMEDOUT) {
+		dev_err(port->dev, "Timeout waiting while UART TX FULL\n");
+		return;
+	}
+}
+
+static void sunplus_uart_console_putchar(struct uart_port *port, int ch)
+{
+	wait_for_xmitr(port);
+	sp_uart_put_char(port, ch);
+}
+
+static void sunplus_console_write(struct console *co,
+				  const char *s,
+				  unsigned int count)
+{
+	unsigned long flags;
+	int locked = 1;
+
+	local_irq_save(flags);
+
+	if (sunplus_console_ports[co->index]->port.sysrq)
+		locked = 0;
+	else if (oops_in_progress)
+		locked = spin_trylock(&sunplus_console_ports[co->index]->port.lock);
+	else
+		spin_lock(&sunplus_console_ports[co->index]->port.lock);
+
+	uart_console_write(&sunplus_console_ports[co->index]->port, s, count,
+			   sunplus_uart_console_putchar);
+
+	if (locked)
+		spin_unlock(&sunplus_console_ports[co->index]->port.lock);
+
+	local_irq_restore(flags);
+}
+
+static int __init sunplus_console_setup(struct console *co, char *options)
+{
+	struct sunplus_uart_port *sup;
+	int baud = 115200;
+	int bits = 8;
+	int parity = 'n';
+	int flow = 'n';
+
+	if (co->index < 0 || co->index >= SUP_UART_NR)
+		return -EINVAL;
+
+	sup = sunplus_console_ports[co->index];
+	if (!sup)
+		return -ENODEV;
+
+	if (options)
+		uart_parse_options(options, &baud, &parity, &bits, &flow);
+
+	return uart_set_options(&sup->port, co, baud, parity, bits, flow);
+}
+
+static struct uart_driver sunplus_uart_driver;
+static struct console sunplus_uart_console = {
+	.name		= "ttySUP",
+	.write		= sunplus_console_write,
+	.device		= uart_console_device,
+	.setup		= sunplus_console_setup,
+	.flags		= CON_PRINTBUFFER,
+	.index		= -1,
+	.data		= &sunplus_uart_driver
+};
+
+static int __init sunplus_console_init(void)
+{
+	register_console(&sunplus_uart_console);
+	return 0;
+}
+console_initcall(sunplus_console_init);
+#endif
+
+static struct uart_driver sunplus_uart_driver = {
+	.owner		= THIS_MODULE,
+	.driver_name	= "sunplus_uart",
+	.dev_name	= "ttySUP",
+	.major		= TTY_MAJOR,
+	.minor		= 64,
+	.nr		= SUP_UART_NR,
+	.cons		= NULL,
+};
+
+static int sunplus_uart_probe(struct platform_device *pdev)
+{
+	struct sunplus_uart_port *sup;
+	struct uart_port *port;
+	struct resource *res;
+	int ret, irq;
+
+	pdev->id = of_alias_get_id(pdev->dev.of_node, "serial");
+
+	if (pdev->id < 0 || pdev->id >= SUP_UART_NR)
+		return -EINVAL;
+
+	sup = devm_kzalloc(&pdev->dev, sizeof(*sup), GFP_KERNEL);
+	if (!sup)
+		return -ENOMEM;
+
+	sup->clk = devm_clk_get_optional(&pdev->dev, NULL);
+	if (IS_ERR(sup->clk))
+		return dev_err_probe(&pdev->dev, PTR_ERR(sup->clk), "clk not found\n");
+
+	ret = clk_prepare_enable(sup->clk);
+	if (ret)
+		return ret;
+
+	ret = devm_add_action_or_reset(&pdev->dev,
+				       (void(*)(void *))clk_disable_unprepare,
+				       sup->clk);
+	if (ret)
+		return ret;
+
+	sup->rstc = devm_reset_control_get_exclusive(&pdev->dev, NULL);
+	if (IS_ERR(sup->rstc))
+		return dev_err_probe(&pdev->dev, PTR_ERR(sup->rstc), "rstc not found\n");
+
+	port = &sup->port;
+
+	port->membase = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
+	if (IS_ERR(port->membase))
+		return dev_err_probe(&pdev->dev, PTR_ERR(port->membase), "membase not found\n");
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return irq;
+
+	port->mapbase = res->start;
+	port->uartclk = clk_get_rate(sup->clk);
+	port->line = pdev->id;
+	port->irq = irq;
+	port->dev = &pdev->dev;
+	port->iotype = UPIO_MEM;
+	port->ops = &sunplus_uart_ops;
+	port->flags = UPF_BOOT_AUTOCONF;
+	port->fifosize = 128;
+
+	ret = reset_control_deassert(sup->rstc);
+	if (ret)
+		return ret;
+
+	ret = devm_add_action_or_reset(&pdev->dev,
+				       (void(*)(void *))reset_control_assert,
+				       sup->rstc);
+	if (ret)
+		return ret;
+
+#ifdef CONFIG_SERIAL_SUNPLUS_CONSOLE
+	sunplus_console_ports[sup->port.line] = sup;
+#endif
+
+	platform_set_drvdata(pdev, &sup->port);
+
+	ret = uart_add_one_port(&sunplus_uart_driver, &sup->port);
+#ifdef CONFIG_SERIAL_SUNPLUS_CONSOLE
+	if (ret)
+		sunplus_console_ports[sup->port.line] = NULL;
+#endif
+
+	return ret;
+}
+
+static int sunplus_uart_remove(struct platform_device *pdev)
+{
+	struct sunplus_uart_port *sup = platform_get_drvdata(pdev);
+
+	uart_remove_one_port(&sunplus_uart_driver, &sup->port);
+
+	return 0;
+}
+
+static int sunplus_uart_suspend(struct device *dev)
+{
+	struct sunplus_uart_port *sup = dev_get_drvdata(dev);
+
+	if (!uart_console(&sup->port))
+		uart_suspend_port(&sunplus_uart_driver, &sup->port);
+
+	return 0;
+}
+
+static int sunplus_uart_resume(struct device *dev)
+{
+	struct sunplus_uart_port *sup = dev_get_drvdata(dev);
+
+	if (!uart_console(&sup->port))
+		uart_resume_port(&sunplus_uart_driver, &sup->port);
+
+	return 0;
+}
+
+static const struct dev_pm_ops sunplus_uart_pm_ops = {
+	SET_SYSTEM_SLEEP_PM_OPS(sunplus_uart_suspend, sunplus_uart_resume)
+};
+
+static const struct of_device_id sp_uart_of_match[] = {
+	{ .compatible = "sunplus,sp7021-uart" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, sp_uart_of_match);
+
+static struct platform_driver sunplus_uart_platform_driver = {
+	.probe		= sunplus_uart_probe,
+	.remove		= sunplus_uart_remove,
+	.driver = {
+		.name	= "sunplus_uart",
+		.of_match_table = sp_uart_of_match,
+		.pm     = &sunplus_uart_pm_ops,
+	}
+};
+
+static int __init sunplus_uart_init(void)
+{
+	int ret;
+
+#ifdef CONFIG_SERIAL_SUNPLUS_CONSOLE
+	sunplus_uart_driver.cons = &sunplus_uart_console;
+#endif
+
+	ret = uart_register_driver(&sunplus_uart_driver);
+	if (ret)
+		return ret;
+
+	ret = platform_driver_register(&sunplus_uart_platform_driver);
+	if (ret)
+		uart_unregister_driver(&sunplus_uart_driver);
+
+	return ret;
+}
+module_init(sunplus_uart_init);
+
+static void __exit sunplus_uart_exit(void)
+{
+	platform_driver_unregister(&sunplus_uart_platform_driver);
+	uart_unregister_driver(&sunplus_uart_driver);
+}
+module_exit(sunplus_uart_exit);
+
+#ifdef CONFIG_SERIAL_EARLYCON
+static void sunplus_uart_putc(struct uart_port *port, int c)
+{
+	unsigned int val;
+	int ret;
+
+	ret = readl_poll_timeout_atomic(port->membase + SUP_UART_LSR, val,
+					(val & UART_LSR_TEMT), 1, 10000);
+	if (ret)
+		return;
+
+	writel(c, port->membase + SUP_UART_DATA);
+}
+
+static void sunplus_uart_early_write(struct console *con, const char *s, unsigned int n)
+{
+	struct earlycon_device *dev = con->data;
+
+	uart_console_write(&dev->port, s, n, sunplus_uart_putc);
+}
+
+static int __init
+sunplus_uart_early_setup(struct earlycon_device *dev, const char *opt)
+{
+	if (!(dev->port.membase || dev->port.iobase))
+		return -ENODEV;
+
+	dev->con->write = sunplus_uart_early_write;
+
+	return 0;
+}
+OF_EARLYCON_DECLARE(sunplus_uart, "sunplus,sp7021-uart", sunplus_uart_early_setup);
+#endif
+
+MODULE_DESCRIPTION("Sunplus UART driver");
+MODULE_AUTHOR("Hammer Hsieh <hammerh0314@gmail.com>");
+MODULE_LICENSE("GPL v2");
diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h
index c4042dc..2dfe443 100644
--- a/include/uapi/linux/serial_core.h
+++ b/include/uapi/linux/serial_core.h
@@ -274,4 +274,7 @@
 /* Freescale LINFlexD UART */
 #define PORT_LINFLEXUART	122
 
+/* Sunplus UART */
+#define PORT_SUNPLUS	123
+
 #endif /* _UAPILINUX_SERIAL_CORE_H */
-- 
2.7.4

Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

[Jiri Slaby]

Hi,

On 12. 01. 22, 10:24, Hammer Hsieh wrote:
> Add Sunplus SoC UART Driver
...
> --- /dev/null
> +++ b/drivers/tty/serial/sunplus-uart.c
> @@ -0,0 +1,756 @@
...
> +/* Register offsets */
> +#define SUP_UART_DATA			0x00
> +#define SUP_UART_LSR			0x04
> +#define SUP_UART_MSR			0x08
> +#define SUP_UART_LCR			0x0C
> +#define SUP_UART_MCR			0x10
> +#define SUP_UART_DIV_L			0x14
> +#define SUP_UART_DIV_H			0x18
> +#define SUP_UART_ISC			0x1C
> +#define SUP_UART_TX_RESIDUE		0x20
> +#define SUP_UART_RX_RESIDUE		0x24
> +
> +/* Line Status Register bits */
> +#define SUP_UART_LSR_BC			BIT(5) /* break condition status */
> +#define SUP_UART_LSR_FE			BIT(4) /* frame error status */
> +#define SUP_UART_LSR_OE			BIT(3) /* overrun error status */
> +#define SUP_UART_LSR_PE			BIT(2) /* parity error status */

I just wonder why do the HW creators feel so creative to redefine the 
world...

> +static void sunplus_shutdown(struct uart_port *port)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&port->lock, flags);
> +	writel(0, port->membase + SUP_UART_ISC);
> +	spin_unlock_irqrestore(&port->lock, flags);

I asked last time:
* What bus is this -- posting?

You replied:
* Here just clear interrupt.
* Not really understand your comment?

So I am asking again:
What bus is this? Isn't a posted write a problem here? I mean, shouldn't 
you read from the register so that the write hits the device? That 
depends on the bus this sits on, so just asking.

Other than that the driver looks much better now, i.e. LGTM.

thanks,
-- 
js
suse labs

Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

[hammer hsieh]

Jiri Slaby <jirislaby@kernel.org> 於 2022年1月13日 週四 下午3:06寫道：
>
> Hi,
>
> On 12. 01. 22, 10:24, Hammer Hsieh wrote:
> > Add Sunplus SoC UART Driver
> ...
> > --- /dev/null
> > +++ b/drivers/tty/serial/sunplus-uart.c
> > @@ -0,0 +1,756 @@
> ...
> > +/* Register offsets */
> > +#define SUP_UART_DATA                        0x00
> > +#define SUP_UART_LSR                 0x04
> > +#define SUP_UART_MSR                 0x08
> > +#define SUP_UART_LCR                 0x0C
> > +#define SUP_UART_MCR                 0x10
> > +#define SUP_UART_DIV_L                       0x14
> > +#define SUP_UART_DIV_H                       0x18
> > +#define SUP_UART_ISC                 0x1C
> > +#define SUP_UART_TX_RESIDUE          0x20
> > +#define SUP_UART_RX_RESIDUE          0x24
> > +
> > +/* Line Status Register bits */
> > +#define SUP_UART_LSR_BC                      BIT(5) /* break condition status */
> > +#define SUP_UART_LSR_FE                      BIT(4) /* frame error status */
> > +#define SUP_UART_LSR_OE                      BIT(3) /* overrun error status */
> > +#define SUP_UART_LSR_PE                      BIT(2) /* parity error status */
>
> I just wonder why do the HW creators feel so creative to redefine the
> world...
>

Our IC designer create it, I just try to make it work.
Indeed, before Greg KH mentioned 8250-like, I didn't realize our uart
so much like 8250.
Thanks for your review.

> > +static void sunplus_shutdown(struct uart_port *port)
> > +{
> > +     unsigned long flags;
> > +
> > +     spin_lock_irqsave(&port->lock, flags);
> > +     writel(0, port->membase + SUP_UART_ISC);
> > +     spin_unlock_irqrestore(&port->lock, flags);
>
> I asked last time:
> * What bus is this -- posting?
>
> You replied:
> * Here just clear interrupt.
> * Not really understand your comment?
>
> So I am asking again:
> What bus is this? Isn't a posted write a problem here? I mean, shouldn't
> you read from the register so that the write hits the device? That
> depends on the bus this sits on, so just asking.
>

Each UART has its own ISC register.
Ex.
dev/ttySUP0 base_adr = 0x9C00-0000 , isc_addr = 0x9C00-001C
dev/ttySUP1 base_adr = 0x9C00-0080 , isc_addr = 0x9C00-009C
dev/ttySUP2 base_adr = 0x9C00-0100 , isc_addr = 0x9C00-011C
dev/ttySUP3 base_adr = 0x9C00-0180 , isc_addr = 0x9C00-019C
dev/ttySUP4 base_adr = 0x9C00-0200 , isc_addr = 0x9C00-021C
So sunplus_shutdown() just simply turn off its own device isc only.
That's why I didn't read register value, just write 0 for it.

> Other than that the driver looks much better now, i.e. LGTM.
>
> thanks,
> --
> js
> suse labs

Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

[Jiri Slaby]

On 13. 01. 22, 9:54, hammer hsieh wrote:
>>> +static void sunplus_shutdown(struct uart_port *port)
>>> +{
>>> +     unsigned long flags;
>>> +
>>> +     spin_lock_irqsave(&port->lock, flags);
>>> +     writel(0, port->membase + SUP_UART_ISC);
>>> +     spin_unlock_irqrestore(&port->lock, flags);
>>
>> I asked last time:
>> * What bus is this -- posting?
>>
>> You replied:
>> * Here just clear interrupt.
>> * Not really understand your comment?
>>
>> So I am asking again:
>> What bus is this? Isn't a posted write a problem here? I mean, shouldn't
>> you read from the register so that the write hits the device? That
>> depends on the bus this sits on, so just asking.
>>
> 
> Each UART has its own ISC register.
> Ex.
> dev/ttySUP0 base_adr = 0x9C00-0000 , isc_addr = 0x9C00-001C
> dev/ttySUP1 base_adr = 0x9C00-0080 , isc_addr = 0x9C00-009C
> dev/ttySUP2 base_adr = 0x9C00-0100 , isc_addr = 0x9C00-011C
> dev/ttySUP3 base_adr = 0x9C00-0180 , isc_addr = 0x9C00-019C
> dev/ttySUP4 base_adr = 0x9C00-0200 , isc_addr = 0x9C00-021C
> So sunplus_shutdown() just simply turn off its own device isc only.
> That's why I didn't read register value, just write 0 for it.

Could you explain me what posted write is and how does it not matter in 
this case?

thanks,
-- 
js
suse labs

Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

[hammer hsieh]

Jiri Slaby <jirislaby@kernel.org> 於 2022年1月13日 週四 下午5:08寫道：
>
> On 13. 01. 22, 9:54, hammer hsieh wrote:
> >>> +static void sunplus_shutdown(struct uart_port *port)
> >>> +{
> >>> +     unsigned long flags;
> >>> +
> >>> +     spin_lock_irqsave(&port->lock, flags);
> >>> +     writel(0, port->membase + SUP_UART_ISC);
> >>> +     spin_unlock_irqrestore(&port->lock, flags);
> >>
> >> I asked last time:
> >> * What bus is this -- posting?
> >>
> >> You replied:
> >> * Here just clear interrupt.
> >> * Not really understand your comment?
> >>
> >> So I am asking again:
> >> What bus is this? Isn't a posted write a problem here? I mean, shouldn't
> >> you read from the register so that the write hits the device? That
> >> depends on the bus this sits on, so just asking.
> >>
> >
> > Each UART has its own ISC register.
> > Ex.
> > dev/ttySUP0 base_adr = 0x9C00-0000 , isc_addr = 0x9C00-001C
> > dev/ttySUP1 base_adr = 0x9C00-0080 , isc_addr = 0x9C00-009C
> > dev/ttySUP2 base_adr = 0x9C00-0100 , isc_addr = 0x9C00-011C
> > dev/ttySUP3 base_adr = 0x9C00-0180 , isc_addr = 0x9C00-019C
> > dev/ttySUP4 base_adr = 0x9C00-0200 , isc_addr = 0x9C00-021C
> > So sunplus_shutdown() just simply turn off its own device isc only.
> > That's why I didn't read register value, just write 0 for it.
>
> Could you explain me what posted write is and how does it not matter in
> this case?
>

Each UART ISC register contains

Bit7 MSM(Modem Status) INT enable / disable (Access type RW) not use
now (0: default)
Bit6 LSM(Line Status) INT  enable / disable  (Access type RW) not use
now(0: default)
Bit5 RXM INT enable / disable  (Access type RW) set this
Bit4 TXM INT enable / disable  (Access type RW) set this

Bit3 MS(Modem Status) INT flag (Access type Read only) not use now (0: default)
Bit2 LS(Line Status) INT flag (Access type Read only) not use now (0: default)
Bit1 RX INT flag (Access type Read only) read this
Bit0 TX INT flag (Access type Read only) read this

sunplus_shutdown()
main purpose is to turn off TX INT(bit4) and RX INT(bit5)
bit7 and bit6 not used, should be 0.
bit3 ~ bit0 read only, no effect while writing 0 to them.

> thanks,
> --
> js
> suse labs

Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

[Jiri Slaby]

On 13. 01. 22, 11:56, hammer hsieh wrote:
>> Could you explain me what posted write is and how does it not matter in
>> this case?
>>
> 
> Each UART ISC register contains

No, you still don't follow what I write. Use your favorite web search 
for "posted write" and/or consult with your HW team.

-- 
js
suse labs

Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

[hammer hsieh]

Jiri Slaby <jirislaby@kernel.org> 於 2022年1月13日 週四 下午7:12寫道：
>
> On 13. 01. 22, 11:56, hammer hsieh wrote:
> >> Could you explain me what posted write is and how does it not matter in
> >> this case?
> >>
> >
> > Each UART ISC register contains
>
> No, you still don't follow what I write. Use your favorite web search
> for "posted write" and/or consult with your HW team.
>

Maybe this time, we are on the same page.
Our SP7021 chipset is designed on ARM Cortex-A7 Quad core.
Register Access through AMBA(AXI bus), and it is non-cached.

Did you mean
case1 have concern about "posted write", and you want to know why it not matter?
case2 will be safer?

Case1 :
spin_lock_irq_save()
writel(0, target register)
spin_unlock_irqrestore()
Case2 :
spin_lock_irq_save()
tmp = readl(target register)
tmp &= ~(bit4 | bit5)
writel(tmp, target register)
spin_unlock_irqrestore()

I test uart port with linux-serial-test tool.
Ex. send char
linux-serial-test -y 0x55 -z 0x31 -p /dev/ttySUPx -b 115200
driver will call from uart startup till uart shutdown.
And it works fine, so I didn't think about "posted write" on Register bus.

> --
> js
> suse labs

Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

[Greg KH]

On Fri, Jan 14, 2022 at 10:22:56AM +0800, hammer hsieh wrote:
> Jiri Slaby <jirislaby@kernel.org> 於 2022年1月13日 週四 下午7:12寫道：
> >
> > On 13. 01. 22, 11:56, hammer hsieh wrote:
> > >> Could you explain me what posted write is and how does it not matter in
> > >> this case?
> > >>
> > >
> > > Each UART ISC register contains
> >
> > No, you still don't follow what I write. Use your favorite web search
> > for "posted write" and/or consult with your HW team.
> >
> 
> Maybe this time, we are on the same page.
> Our SP7021 chipset is designed on ARM Cortex-A7 Quad core.
> Register Access through AMBA(AXI bus), and it is non-cached.
> 
> Did you mean
> case1 have concern about "posted write", and you want to know why it not matter?
> case2 will be safer?
> 
> Case1 :
> spin_lock_irq_save()
> writel(0, target register)
> spin_unlock_irqrestore()

A lock does not mean that your write made it to the device.  Please talk
to the hardware designers to properly determine how to correctly write
to the hardware and "know" that the write succeeded or not.  This driver
does not seem to take that into consideration at all.

thanks,

greg k-h

Re: [PATCH v6 2/2] serial:sunplus-uart:Add Sunplus SoC UART Driver

[hammer hsieh]

Hi, Greg KH:

I review all driver again.
I think only startup and shutdown not good.
I will modify like below.
If you are ok, I will submit next patch.

static int sunplus_startup(struct uart_port *port)
{
        unsigned long flags;
        unsigned int isc;
        int ret;

        ret = request_irq(port->irq, sunplus_uart_irq, 0, "sunplus_uart", port);
        if (ret)
                return ret;

        spin_lock_irqsave(&port->lock, flags);

        isc = readl(port->membase + SUP_UART_ISC); //add this line
        isc |= SUP_UART_ISC_RXM;
        writel(isc, port->membase + SUP_UART_ISC);

        spin_unlock_irqrestore(&port->lock, flags);

        return 0;
}

static void sunplus_shutdown(struct uart_port *port)
{
        unsigned long flags;
        unsigned int isc;

        spin_lock_irqsave(&port->lock, flags);

        isc = readl(port->membase + SUP_UART_ISC); //add this line
        isc &= ~(SUP_UART_ISC_RXM | SUP_UART_ISC_TXM); //add this line
        writel(isc, port->membase + SUP_UART_ISC); //modify this line

        spin_unlock_irqrestore(&port->lock, flags);

        free_irq(port->irq, port);
}

Greg KH <gregkh@linuxfoundation.org> 於 2022年1月26日 週三 下午9:47寫道：
>
> On Fri, Jan 14, 2022 at 10:22:56AM +0800, hammer hsieh wrote:
> > Jiri Slaby <jirislaby@kernel.org> 於 2022年1月13日 週四 下午7:12寫道：
> > >
> > > On 13. 01. 22, 11:56, hammer hsieh wrote:
> > > >> Could you explain me what posted write is and how does it not matter in
> > > >> this case?
> > > >>
> > > >
> > > > Each UART ISC register contains
> > >
> > > No, you still don't follow what I write. Use your favorite web search
> > > for "posted write" and/or consult with your HW team.
> > >
> >
> > Maybe this time, we are on the same page.
> > Our SP7021 chipset is designed on ARM Cortex-A7 Quad core.
> > Register Access through AMBA(AXI bus), and it is non-cached.
> >
> > Did you mean
> > case1 have concern about "posted write", and you want to know why it not matter?
> > case2 will be safer?
> >
> > Case1 :
> > spin_lock_irq_save()
> > writel(0, target register)
> > spin_unlock_irqrestore()
>
> A lock does not mean that your write made it to the device.  Please talk
> to the hardware designers to properly determine how to correctly write
> to the hardware and "know" that the write succeeded or not.  This driver
> does not seem to take that into consideration at all.
>
> thanks,
>
> greg k-h