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

Andy Shevchenko
2025-05-02T09:50:54Z

On Wed, Apr 30, 2025 at 07:31:13PM -0500, 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>

Are you just a committer and not a co-developer of this code?

...

> +/*
> + * Serial Port driver for PRUSS UART on TI platforms
> + *
> + * Copyright (C) 2020-2021 by Texas Instruments Incorporated - http://www.ti.com/

My calendar shows 2025...

> + * Author: Bin Liu <b-liu@ti.com>
> + */

...

The list of the inclusions is semi-random. Please, follow the IWYU principle.

> +#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>

Please, no of*.h in a new code.

> +#include <linux/remoteproc.h>

Keep them ordered as well.

+ blank line here.

> +#include "8250.h"

...

> +#define DEFAULT_CLK_SPEED 192000000

Units as a suffix? HZ_PER_MHZ?
You can also fix 8250_omap in the same way.

...

> +static inline void uart_writel(struct uart_port *p, u32 offset, int value)
> +{
> + writel(value, p->membase + (offset << p->regshift));
> +}

Why? Or how does it differ from the ones that serial core provides?

...

> +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)

Please, use usual pattern, check for errors first

if (ret)
return ret;
...
return 0;

> + 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;
> + }

Why?! Please, try to avoid adding more drivers with this ugly hack.

> + 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;

Are you sure it doesn't repeat existing things from other driver(s)?

> +}

...

> +static int pruss8250_probe(struct platform_device *pdev)
> +{
> + struct device_node *np = pdev->dev.of_node;

You don't need this.

> + 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);

Yeah, no modifications from 2021?

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

> + ret = of_alias_get_id(np, "serial");
> + if (ret > 0)
> + up->line = ret;

Use uart_read_port_properties() instead of this and other related code.

> + clk = devm_clk_get(&pdev->dev, NULL);
> + if (IS_ERR(clk)) {
> + if (PTR_ERR(clk) == -EPROBE_DEFER)
> + return -EPROBE_DEFER;

We have other errors which are effectively being ignored here, why?

> + up->uartclk = DEFAULT_CLK_SPEED;
> + } else {
> + up->uartclk = clk_get_rate(clk);

> + devm_clk_put(&pdev->dev, clk);

Why? Maybe you should not to try devm_ to begin with?

> + }
> +
> + 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;
> + }

A lot of this will be simplified by using the above mentioned API.

> + 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);

Why this is needed?

> + return ret;
> +}

...

> +static const struct of_device_id pruss8250_table[] = {
> + { .compatible = "ti,pruss-uart", .data = (void *)PORT_16550A, },

Inner comma is redundant.

> + { /* end of list */ },

No trailing comma in the terminator.

> +};

...

> +config SERIAL_8250_PRUSS
> + tristate "TI PRU-ICSS UART support"
> + depends on SERIAL_8250

> + depends on PRU_REMOTEPROC && TI_PRUSS_INTC

No COMPILE_TEST?

> + 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'.

If m, how would the module be called? See many new driver examples in Kconfigs
(in particular IIO follows this pattern).

--
With Best Regards,
Andy Shevchenko