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

Andrew Davis
2025-05-01T16:28:43Z

On 4/30/25 7:31 PM, Judith Mendez wrote:
> 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;

You never use type, why store it here?

> + 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);

Will the port type ever not be PORT_16550A?

> + 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);

platform_get_resource()

> + if (ret) {
> + dev_err(&pdev->dev, "invalid address\n");
> + return ret;
> + }
> +
> + ret = of_alias_get_id(np, "serial");

Can you make use of the uart_read_port_properties() helper here?

Andrew

> + 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