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

Judith Mendez
2025-05-01T00:31:20Z

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