[PATCH 3/7] 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 or
PRU_ICSS*.

The UART sub-module 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 | 178 +++++++++++++++++++++++++++
 drivers/tty/serial/8250/Kconfig      |  11 ++
 drivers/tty/serial/8250/Makefile     |   1 +
 3 files changed, 190 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..04a455580022
--- /dev/null
+++ b/drivers/tty/serial/8250/8250_pruss.c
@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Serial Port driver for PRUSS UART on TI platforms
+ *
+ *  Copyright (C) 2025 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/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/serial_reg.h>
+#include <linux/serial_core.h>
+
+#include "8250.h"
+
+/* PowerManagement and Emulation */
+#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)
+
+/* Oversampling Mode Select */
+#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_data {
+	struct clk *clk;
+	int line;
+};
+
+static int pruss8250_startup(struct uart_port *port)
+{
+	int ret;
+
+	port->serial_out(port, PRUSS_UART_PEREMU_MGMT, 0);
+
+	ret = serial8250_do_startup(port);
+	if (!ret)
+		port->serial_out(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;
+
+	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;
+	port->serial_out(port, PRUSS_UART_MDR, quot_frac);
+}
+
+static int pruss8250_probe(struct platform_device *pdev)
+{
+	struct uart_8250_port port8250;
+	struct uart_port *port = &port8250.port;
+	struct device *dev = &pdev->dev;
+	struct pruss8250_data *data;
+	struct resource *res;
+	int ret;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	memset(&port8250, 0, sizeof(port8250));
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res) {
+		dev_err(&pdev->dev, "Failed to get resource");
+		return -EINVAL;
+	}
+
+	if (!port->uartclk) {
+		data->clk = devm_clk_get(dev, NULL);
+		if (IS_ERR(data->clk)) {
+			dev_err(dev, "Failed to get clock!\n");
+			return -ENODEV;
+		} else {
+			port->uartclk = clk_get_rate(data->clk);
+			devm_clk_put(dev, data->clk);
+		}
+	}
+
+	port->dev = dev;
+	port->mapbase = res->start;
+	port->mapsize = resource_size(res);
+	port->type = PORT_16550A;
+	port->flags = UPF_BOOT_AUTOCONF | UPF_FIXED_PORT | UPF_FIXED_TYPE |
+		      UPF_IOREMAP;
+	port->startup = pruss8250_startup;
+	port->rs485_config = serial8250_em485_config;
+	port->get_divisor = pruss8250_get_divisor;
+	port->set_divisor = pruss8250_set_divisor;
+
+	ret = uart_read_port_properties(port);
+	if (ret)
+		return ret;
+
+	port->iotype = UPIO_MEM32;
+	port->regshift = 2;
+
+	spin_lock_init(&port8250.port.lock);
+	port8250.capabilities = UART_CAP_FIFO | UART_CAP_AFE;
+
+	ret = serial8250_register_8250_port(&port8250);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "Unable to register 8250 port.\n");
+
+	data->line = ret;
+	platform_set_drvdata(pdev, data);
+	return 0;
+}
+
+static void pruss8250_remove(struct platform_device *pdev)
+{
+	struct pruss8250_data *data = platform_get_drvdata(pdev);
+
+	serial8250_unregister_port(data->line);
+}
+
+static const struct of_device_id pruss8250_of_match[] = {
+	{ .compatible = "ti,pruss-uart", .data = (void *)PORT_16550A },
+	{ /* Sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, pruss8250_of_match);
+
+static struct platform_driver pruss8250_driver = {
+	.driver = {
+		.name = "pruss8250",
+		.of_match_table = pruss8250_of_match,
+	},
+	.probe = pruss8250_probe,
+	.remove = pruss8250_remove,
+};
+
+module_platform_driver(pruss8250_driver);
+
+MODULE_AUTHOR("Bin Liu <b-liu@ti.com");
+MODULE_LICENSE("GPL");
+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..5fdb502b7eae 100644
--- a/drivers/tty/serial/8250/Kconfig
+++ b/drivers/tty/serial/8250/Kconfig
@@ -582,6 +582,17 @@ 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) || COMPILE_TEST
+	help
+	  This driver is to support the UART module in PRU-ICSS which is
+	  available in some TI platforms.
+
+	  To compile this driver as a module, chose M here: the
+	  module will be called 8250_pruss.
+
 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