Re: [PATCH v2 3/5] drivers/tty/serial: add driver for the ESP32 UART

[Jiri Slaby]

On 20. 09. 23, 4:26, Max Filippov wrote:
> Add driver for the UART controllers of the Espressif ESP32 and ESP32S3
> SoCs. Hardware specification is available at the following URLs:
...
> +static void esp32_uart_rxint(struct uart_port *port)
> +{
> +	struct tty_port *tty_port = &port->state->port;
> +	u32 rx_fifo_cnt = esp32_uart_rx_fifo_cnt(port);
> +	unsigned long flags;
> +	u32 i;
> +
> +	if (!rx_fifo_cnt)
> +		return;
> +
> +	spin_lock_irqsave(&port->lock, flags);
> +
> +	for (i = 0; i < rx_fifo_cnt; ++i) {
> +		u32 rx = esp32_uart_read(port, UART_FIFO_REG);
> +		u32 brk = 0;
> +
> +		++port->icount.rx;

Should yuou increment this only in case of insert_flip_char()?

> +		if (!rx) {
> +			brk = esp32_uart_read(port, UART_INT_ST_REG) &
> +				UART_BRK_DET_INT;
> +		}
> +		if (brk) {
> +			esp32_uart_write(port, UART_INT_CLR_REG, brk);
> +			++port->icount.brk;
> +			uart_handle_break(port);
> +		} else {
> +			if (uart_handle_sysrq_char(port, (unsigned char)rx))
> +				continue;
> +			tty_insert_flip_char(tty_port, rx, TTY_NORMAL);
> +		}

This is heavy. Is it equivalent to:
if (!rx && esp32_uart_read(port, UART_INT_ST_REG) &
    UART_BRK_DET_INT) {
  esp32_uart_write(port, UART_INT_CLR_REG, brk);
  ++port->icount.brk;
  uart_handle_break(port);
  continue;
}

if (uart_handle_sysrq_char(port, (unsigned char)rx))
  continue;

tty_insert_flip_char(tty_port, rx, TTY_NORMAL);

?

> +	}
> +	spin_unlock_irqrestore(&port->lock, flags);
> +
> +	tty_flip_buffer_push(tty_port);
> +}
...
> +static void esp32_uart_put_char_sync(struct uart_port *port, u8 c)
> +{
> +	unsigned long timeout;
> +
> +	timeout = jiffies + msecs_to_jiffies(1000);

I.e. plus HZ?

> +	while (esp32_uart_tx_fifo_cnt(port) >= ESP32_UART_TX_FIFO_SIZE) {
> +		if (time_after(jiffies, timeout)) {
> +			dev_warn(port->dev, "timeout waiting for TX FIFO\n");
> +			return;
> +		}
> +		cpu_relax();
> +	}
> +	esp32_uart_put_char(port, c);
> +}
> +
> +static void esp32_uart_transmit_buffer(struct uart_port *port)
> +{
> +	u32 tx_fifo_used = esp32_uart_tx_fifo_cnt(port);
> +
> +	if (tx_fifo_used < ESP32_UART_TX_FIFO_SIZE) {

Invert the condition and return here?

> +		unsigned int pending;
> +		u8 ch;
> +
> +		pending = uart_port_tx_limited(port, ch,
> +					       ESP32_UART_TX_FIFO_SIZE - tx_fifo_used,
> +					       true, esp32_uart_put_char(port, ch),
> +					       ({}));
> +		if (pending) {
> +			u32 int_ena;
> +
> +			int_ena = esp32_uart_read(port, UART_INT_ENA_REG);
> +			int_ena |= UART_TXFIFO_EMPTY_INT;
> +			esp32_uart_write(port, UART_INT_ENA_REG, int_ena);
> +		}
> +	}
> +}


> +static irqreturn_t esp32_uart_int(int irq, void *dev_id)
> +{
> +	struct uart_port *port = dev_id;
> +	u32 status;
> +
> +	status = esp32_uart_read(port, UART_INT_ST_REG);
> +
> +	if (status & (UART_RXFIFO_FULL_INT | UART_BRK_DET_INT))
> +		esp32_uart_rxint(port);
> +	if (status & UART_TXFIFO_EMPTY_INT)
> +		esp32_uart_txint(port);
> +
> +	esp32_uart_write(port, UART_INT_CLR_REG, status);

\n here please.

> +	return IRQ_RETVAL(status);
> +}

> +static int esp32_uart_startup(struct uart_port *port)
> +{
> +	int ret = 0;
> +	unsigned long flags;
> +	struct esp32_port *sport = container_of(port, struct esp32_port, port);
> +
> +	ret = clk_prepare_enable(sport->clk);
> +	if (ret)
> +		return ret;
> +
> +	ret = devm_request_irq(port->dev, port->irq, esp32_uart_int, 0,
> +			       DRIVER_NAME, port);
> +	if (ret) {
> +		clk_disable_unprepare(sport->clk);
> +		return ret;
> +	}
> +
> +	spin_lock_irqsave(&port->lock, flags);
> +	esp32_uart_write(port, UART_CONF1_REG,
> +			 (1 << UART_RXFIFO_FULL_THRHD_SHIFT) |

BIT() ?

> +			 (1 << port_variant(port)->txfifo_empty_thrhd_shift));

And here?

> +	esp32_uart_write(port, UART_INT_CLR_REG, UART_RXFIFO_FULL_INT | UART_BRK_DET_INT);
> +	esp32_uart_write(port, UART_INT_ENA_REG, UART_RXFIFO_FULL_INT | UART_BRK_DET_INT);
> +	spin_unlock_irqrestore(&port->lock, flags);
> +
> +	pr_debug("%s, conf1 = %08x, int_st = %08x, status = %08x\n",
> +		 __func__,
> +		 esp32_uart_read(port, UART_CONF1_REG),
> +		 esp32_uart_read(port, UART_INT_ST_REG),
> +		 esp32_uart_read(port, UART_STATUS_REG));

\n here. Is this debug printout somehow useful?

> +	return ret;
> +}
> +
> +static void esp32_uart_shutdown(struct uart_port *port)
> +{
> +	struct esp32_port *sport = container_of(port, struct esp32_port, port);
> +
> +	esp32_uart_write(port, UART_INT_ENA_REG, 0);
> +	devm_free_irq(port->dev, port->irq, port);

I wonder why to use devm_ after all?

> +	clk_disable_unprepare(sport->clk);
> +}
> +
> +static bool esp32_uart_set_baud(struct uart_port *port, u32 baud)
> +{
> +	u32 div = port->uartclk / baud;
> +	u32 frag = (port->uartclk * 16) / baud - div * 16;
> +
> +	if (div <= port_variant(port)->clkdiv_mask) {
> +		esp32_uart_write(port, UART_CLKDIV_REG,
> +				 div | FIELD_PREP(UART_CLKDIV_FRAG, frag));
> +		return true;
> +	}

\n

> +	return false;
> +}
...
> +static int __init esp32s3_uart_early_console_setup(struct earlycon_device *device,
> +						   const char *options)
> +{
> +	device->port.private_data = (void *)&esp32s3_variant;

No need to cast, right?

\n

> +	return esp32xx_uart_early_console_setup(device, options);
> +}
...
> +static int esp32_uart_probe(struct platform_device *pdev)
> +{
> +	struct device_node *np = pdev->dev.of_node;
> +	static const struct of_device_id *match;
> +	struct uart_port *port;
> +	struct esp32_port *sport;
> +	struct resource *res;
> +	int ret;
> +
> +	match = of_match_device(esp32_uart_dt_ids, &pdev->dev);
> +	if (!match)
> +		return -ENODEV;
> +
> +	sport = devm_kzalloc(&pdev->dev, sizeof(*sport), GFP_KERNEL);
> +	if (!sport)
> +		return -ENOMEM;
> +
> +	port = &sport->port;
> +
> +	ret = of_alias_get_id(np, "serial");
> +	if (ret < 0) {
> +		dev_err(&pdev->dev, "failed to get alias id, errno %d\n", ret);
> +		return ret;
> +	}
> +	if (ret >= UART_NR) {
> +		dev_err(&pdev->dev, "driver limited to %d serial ports\n", UART_NR);
> +		return -ENOMEM;
> +	}
> +
> +	port->line = ret;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (!res)
> +		return -ENODEV;
> +
> +	port->mapbase = res->start;
> +	port->membase = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(port->membase))
> +		return PTR_ERR(port->membase);
> +
> +	sport->clk = devm_clk_get(&pdev->dev, NULL);
> +	if (IS_ERR(sport->clk))
> +		return PTR_ERR(sport->clk);
> +
> +	port->uartclk = clk_get_rate(sport->clk);
> +	port->dev = &pdev->dev;
> +	port->type = PORT_ESP32UART;
> +	port->iotype = UPIO_MEM;
> +	port->irq = platform_get_irq(pdev, 0);
> +	port->ops = &esp32_uart_pops;
> +	port->flags = UPF_BOOT_AUTOCONF;
> +	port->has_sysrq = 1;
> +	port->fifosize = ESP32_UART_TX_FIFO_SIZE;
> +	port->private_data = (void *)match->data;

No need to cast.

> +
> +	esp32_uart_ports[port->line] = sport;
> +
> +	platform_set_drvdata(pdev, port);
> +
> +	return uart_add_one_port(&esp32_uart_reg, port);
> +}

regards,
--
js
suse labs