[PATCH RFC 2/2] serial: 8250: Add PRUSS UART driver

[Judith Mendez <jm@ti.com>]

From: Bin Liu <b-liu@ti.com>

This adds a new serial 8250 driver that supports the UART in PRUSS
module.

The PRUSS has a UART sub-module which is based on the industry standard
TL16C550 UART controller, which has 16-bytes FIFO and supports 16x and
13x over samplings.

Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Judith Mendez <jm@ti.com>
---
 drivers/tty/serial/8250/8250_pruss.c | 213 +++++++++++++++++++++++++++
 drivers/tty/serial/8250/Kconfig      |  10 ++
 drivers/tty/serial/8250/Makefile     |   1 +
 3 files changed, 224 insertions(+)
 create mode 100644 drivers/tty/serial/8250/8250_pruss.c

diff --git a/drivers/tty/serial/8250/8250_pruss.c b/drivers/tty/serial/8250/8250_pruss.c
new file mode 100644
index 000000000000..2943bf7d6645
--- /dev/null
+++ b/drivers/tty/serial/8250/8250_pruss.c
@@ -0,0 +1,213 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Serial Port driver for PRUSS UART on TI platforms
+ *
+ *  Copyright (C) 2020-2021 by Texas Instruments Incorporated - http://www.ti.com/
+ *  Author: Bin Liu <b-liu@ti.com>
+ */
+#include <linux/clk.h>
+#include <linux/module.h>
+#include <linux/serial_reg.h>
+#include <linux/serial_core.h>
+#include <linux/of_irq.h>
+#include <linux/of_address.h>
+#include <linux/of_platform.h>
+#include <linux/remoteproc.h>
+#include "8250.h"
+
+#define DEFAULT_CLK_SPEED	192000000
+
+/* extra registers */
+#define PRUSS_UART_PEREMU_MGMT	12
+#define PRUSS_UART_TX_EN	BIT(14)
+#define PRUSS_UART_RX_EN	BIT(13)
+#define PRUSS_UART_FREE_RUN	BIT(0)
+
+#define PRUSS_UART_MDR			13
+#define PRUSS_UART_MDR_OSM_SEL_MASK	BIT(0)
+#define PRUSS_UART_MDR_16X_MODE		0
+#define PRUSS_UART_MDR_13X_MODE		1
+
+struct pruss8250_info {
+	int type;
+	int line;
+};
+
+static inline void uart_writel(struct uart_port *p, u32 offset, int value)
+{
+	writel(value, p->membase + (offset << p->regshift));
+}
+
+static int pruss8250_startup(struct uart_port *port)
+{
+	int ret;
+
+	uart_writel(port, PRUSS_UART_PEREMU_MGMT, 0);
+
+	ret = serial8250_do_startup(port);
+	if (!ret)
+		uart_writel(port, PRUSS_UART_PEREMU_MGMT, PRUSS_UART_TX_EN |
+							  PRUSS_UART_RX_EN |
+							  PRUSS_UART_FREE_RUN);
+	return ret;
+}
+
+static unsigned int pruss8250_get_divisor(struct uart_port *port,
+					  unsigned int baud,
+					  unsigned int *frac)
+{
+	unsigned int uartclk = port->uartclk;
+	unsigned int div_13, div_16;
+	unsigned int abs_d13, abs_d16;
+	u16 quot;
+
+	/* Old custom speed handling */
+	if (baud == 38400 && (port->flags & UPF_SPD_MASK) == UPF_SPD_CUST) {
+		quot = port->custom_divisor & UART_DIV_MAX;
+		if (port->custom_divisor & (1 << 16))
+			*frac = PRUSS_UART_MDR_13X_MODE;
+		else
+			*frac = PRUSS_UART_MDR_16X_MODE;
+
+		return quot;
+	}
+
+	div_13 = DIV_ROUND_CLOSEST(uartclk, 13 * baud);
+	div_16 = DIV_ROUND_CLOSEST(uartclk, 16 * baud);
+	div_13 = div_13 ? : 1;
+	div_16 = div_16 ? : 1;
+
+	abs_d13 = abs(baud - uartclk / 13 / div_13);
+	abs_d16 = abs(baud - uartclk / 16 / div_16);
+
+	if (abs_d13 >= abs_d16) {
+		*frac = PRUSS_UART_MDR_16X_MODE;
+		quot = div_16;
+	} else {
+		*frac = PRUSS_UART_MDR_13X_MODE;
+		quot = div_13;
+	}
+
+	return quot;
+}
+
+static void pruss8250_set_divisor(struct uart_port *port, unsigned int baud,
+				  unsigned int quot, unsigned int quot_frac)
+{
+	serial8250_do_set_divisor(port, baud, quot);
+	/*
+	 * quot_frac holds the MDR over-sampling mode
+	 * which is set in pruss8250_get_divisor()
+	 */
+	quot_frac &= PRUSS_UART_MDR_OSM_SEL_MASK;
+	serial_port_out(port, PRUSS_UART_MDR, quot_frac);
+}
+
+static int pruss8250_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct uart_8250_port port8250;
+	struct uart_port *up = &port8250.port;
+	struct pruss8250_info *info;
+	struct resource resource;
+	unsigned int port_type;
+	struct clk *clk;
+	int ret;
+
+	port_type = (unsigned long)of_device_get_match_data(&pdev->dev);
+	if (port_type == PORT_UNKNOWN)
+		return -EINVAL;
+
+	info = devm_kzalloc(&pdev->dev, sizeof(*info), GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	memset(&port8250, 0, sizeof(port8250));
+
+	ret = of_address_to_resource(np, 0, &resource);
+	if (ret) {
+		dev_err(&pdev->dev, "invalid address\n");
+		return ret;
+	}
+
+	ret = of_alias_get_id(np, "serial");
+	if (ret > 0)
+		up->line = ret;
+
+	clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(clk)) {
+		if (PTR_ERR(clk) == -EPROBE_DEFER)
+			return -EPROBE_DEFER;
+		up->uartclk = DEFAULT_CLK_SPEED;
+	} else {
+		up->uartclk = clk_get_rate(clk);
+		devm_clk_put(&pdev->dev, clk);
+	}
+
+	up->dev = &pdev->dev;
+	up->mapbase = resource.start;
+	up->mapsize = resource_size(&resource);
+	up->type = port_type;
+	up->iotype = UPIO_MEM;
+	up->regshift = 2;
+	up->flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF | UPF_FIXED_PORT |
+		    UPF_FIXED_TYPE | UPF_IOREMAP;
+	up->irqflags |= IRQF_SHARED;
+	up->startup = pruss8250_startup;
+	up->rs485_config = serial8250_em485_config;
+	up->get_divisor = pruss8250_get_divisor;
+	up->set_divisor = pruss8250_set_divisor;
+
+	ret = of_irq_get(np, 0);
+	if (ret < 0) {
+		if (ret != -EPROBE_DEFER)
+			dev_err(&pdev->dev, "missing irq\n");
+		return ret;
+	}
+
+	up->irq = ret;
+	spin_lock_init(&port8250.port.lock);
+	port8250.capabilities = UART_CAP_FIFO | UART_CAP_AFE;
+
+	ret = serial8250_register_8250_port(&port8250);
+	if (ret < 0)
+		goto err_dispose;
+
+	info->type = port_type;
+	info->line = ret;
+	platform_set_drvdata(pdev, info);
+
+	return 0;
+
+err_dispose:
+	irq_dispose_mapping(port8250.port.irq);
+	return ret;
+}
+
+static void pruss8250_remove(struct platform_device *pdev)
+{
+	struct pruss8250_info *info = platform_get_drvdata(pdev);
+
+	serial8250_unregister_port(info->line);
+}
+
+static const struct of_device_id pruss8250_table[] = {
+	{ .compatible = "ti,pruss-uart", .data = (void *)PORT_16550A, },
+	{ /* end of list */ },
+};
+MODULE_DEVICE_TABLE(of, pruss8250_table);
+
+static struct platform_driver pruss8250_driver = {
+	.driver = {
+		.name = "pruss8250",
+		.of_match_table = pruss8250_table,
+	},
+	.probe = pruss8250_probe,
+	.remove = pruss8250_remove,
+};
+
+module_platform_driver(pruss8250_driver);
+
+MODULE_AUTHOR("Bin Liu <b-liu@ti.com");
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("Serial Port driver for PRUSS UART on TI platforms");
diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
index f64ef0819cd4..cd4346609c55 100644
--- a/drivers/tty/serial/8250/Kconfig
+++ b/drivers/tty/serial/8250/Kconfig
@@ -582,6 +582,16 @@ config SERIAL_8250_NI
 	  To compile this driver as a module, choose M here: the module
 	  will be called 8250_ni.
 
+config SERIAL_8250_PRUSS
+	tristate "TI PRU-ICSS UART support"
+	depends on SERIAL_8250
+	depends on PRU_REMOTEPROC && TI_PRUSS_INTC
+	help
+	  This driver is to support the UART module in PRU-ICSS which is
+	  available in some TI platforms.
+	  Say 'Y' here if you wish to use PRU-ICSS UART.
+	  Otherwise, say 'N'.
+
 config SERIAL_OF_PLATFORM
 	tristate "Devicetree based probing for 8250 ports"
 	depends on SERIAL_8250 && OF
diff --git a/drivers/tty/serial/8250/Makefile b/drivers/tty/serial/8250/Makefile
index b04eeda03b23..3132b4f40a34 100644
--- a/drivers/tty/serial/8250/Makefile
+++ b/drivers/tty/serial/8250/Makefile
@@ -47,6 +47,7 @@ obj-$(CONFIG_SERIAL_8250_PARISC)	+= 8250_parisc.o
 obj-$(CONFIG_SERIAL_8250_PCI)		+= 8250_pci.o
 obj-$(CONFIG_SERIAL_8250_PCI1XXXX)	+= 8250_pci1xxxx.o
 obj-$(CONFIG_SERIAL_8250_PERICOM)	+= 8250_pericom.o
+obj-$(CONFIG_SERIAL_8250_PRUSS)		+= 8250_pruss.o
 obj-$(CONFIG_SERIAL_8250_PXA)		+= 8250_pxa.o
 obj-$(CONFIG_SERIAL_8250_RT288X)	+= 8250_rt288x.o
 obj-$(CONFIG_SERIAL_8250_CS)		+= serial_cs.o
-- 
2.49.0