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

Judith Mendez
2025-05-08T22:11:42Z

Hi Andrew,

On 5/1/25 11:28 AM, Andrew Davis wrote:
> 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?

removed

>
>> +    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?

So far each UART module is has been the same, I think it might be safe
to hardcode:

port->type = 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()

Will add

>
>> +    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?

yes we can,
thanks for reviewing.

~ Judith

>
> 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