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Date:   Thu, 14 Sep 2023 16:07:15 +0300 (EEST)
From:   =?ISO-8859-15?Q?Ilpo_J=E4rvinen?= <ilpo.jarvinen@linux.intel.com>
To:     Max Filippov <jcmvbkbc@gmail.com>
cc:     LKML <linux-kernel@vger.kernel.org>,
        linux-serial <linux-serial@vger.kernel.org>,
        devicetree@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>
Subject: Re: [PATCH 2/4] drivers/tty/serial: add driver for the ESP32 UART
In-Reply-To: <20230913211449.668796-3-jcmvbkbc@gmail.com>
Message-ID: <13c43e44-aaee-c44-a32-87febd81379c@linux.intel.com>
References: <20230913211449.668796-1-jcmvbkbc@gmail.com> <20230913211449.668796-3-jcmvbkbc@gmail.com>
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On Wed, 13 Sep 2023, Max Filippov wrote:

> Add driver for the UART controllers of the Espressif ESP32 and ESP32S3
> SoCs. Hardware specification is available at the following URLs:
> 
>   https://www.espressif.com/sites/default/files/documentation/esp32_technical_reference_manual_en.pdf
>   (Chapter 13 UART Controller)
>   https://www.espressif.com/sites/default/files/documentation/esp32-s3_technical_reference_manual_en.pdf
>   (Chapter 26 UART Controller)
> 
> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
> ---
>  drivers/tty/serial/Kconfig       |  13 +
>  drivers/tty/serial/Makefile      |   1 +
>  drivers/tty/serial/esp32_uart.c  | 766 +++++++++++++++++++++++++++++++
>  include/uapi/linux/serial_core.h |   3 +
>  4 files changed, 783 insertions(+)
>  create mode 100644 drivers/tty/serial/esp32_uart.c
> 
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index bdc568a4ab66..d9ca6b268f01 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -1578,6 +1578,19 @@ config SERIAL_NUVOTON_MA35D1_CONSOLE
>  	  but you can alter that using a kernel command line option such as
>  	  "console=ttyNVTx".
>  
> +config SERIAL_ESP32
> +	tristate "Espressif ESP32 UART support"
> +	depends on XTENSA_PLATFORM_ESP32 || (COMPILE_TEST && OF)
> +	select SERIAL_CORE
> +	select SERIAL_CORE_CONSOLE
> +	select SERIAL_EARLYCON
> +	help
> +	  Driver for the UART controllers of the Espressif ESP32xx SoCs.
> +	  When earlycon option is enabled the following kernel command line
> +	  snippets may be used:
> +	    earlycon=esp32s3uart,mmio32,0x60000000,115200n8,40000000
> +	    earlycon=esp32uart,mmio32,0x3ff40000,115200n8
> +
>  endmenu
>  
>  config SERIAL_MCTRL_GPIO
> diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
> index 138abbc89738..7b73137df7f3 100644
> --- a/drivers/tty/serial/Makefile
> +++ b/drivers/tty/serial/Makefile
> @@ -88,6 +88,7 @@ obj-$(CONFIG_SERIAL_MILBEAUT_USIO) += milbeaut_usio.o
>  obj-$(CONFIG_SERIAL_SIFIVE)	+= sifive.o
>  obj-$(CONFIG_SERIAL_LITEUART) += liteuart.o
>  obj-$(CONFIG_SERIAL_SUNPLUS)	+= sunplus-uart.o
> +obj-$(CONFIG_SERIAL_ESP32)	+= esp32_uart.o
>  
>  # GPIOLIB helpers for modem control lines
>  obj-$(CONFIG_SERIAL_MCTRL_GPIO)	+= serial_mctrl_gpio.o
> diff --git a/drivers/tty/serial/esp32_uart.c b/drivers/tty/serial/esp32_uart.c
> new file mode 100644
> index 000000000000..05ec0fce3a62
> --- /dev/null
> +++ b/drivers/tty/serial/esp32_uart.c
> @@ -0,0 +1,766 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +
> +#include <linux/clk.h>
> +#include <linux/console.h>
> +#include <linux/io.h>
> +#include <linux/irq.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/serial_core.h>
> +#include <linux/slab.h>
> +#include <linux/tty_flip.h>
> +#include <linux/delay.h>
> +#include <asm/serial.h>
> +
> +#define DRIVER_NAME	"esp32-uart"
> +#define DEV_NAME	"ttyS"
> +#define UART_NR		3
> +
> +#define ESP32_UART_TX_FIFO_SIZE	127
> +#define ESP32_UART_RX_FIFO_SIZE	127
> +
> +#define UART_FIFO_REG			0x00
> +#define UART_INT_RAW_REG		0x04
> +#define UART_INT_ST_REG			0x08
> +#define UART_INT_ENA_REG		0x0c
> +#define UART_INT_CLR_REG		0x10
> +#define UART_RXFIFO_FULL_INT_MASK		0x00000001
> +#define UART_TXFIFO_EMPTY_INT_MASK		0x00000002
> +#define UART_BRK_DET_INT_MASK			0x00000080

Use BIT() for these and do not call them MASK if they're just for a single 
flag bit.

> +#define UART_CLKDIV_REG			0x14
> +#define ESP32_UART_CLKDIV_MASK			0x000fffff
> +#define ESP32S3_UART_CLKDIV_MASK		0x00000fff
> +#define UART_CLKDIV_SHIFT			0

Use GENMASK() and drop the related *_SHIFT defines as 
FIELD_GET()/FIELD_PREP() will not need it.

Usually _MASK postfix is just waste of screen space and provides no useful 
information so consider dropping that as well from the names.

> +#define UART_CLKDIV_FRAG_MASK			0x00f00000
> +#define UART_CLKDIV_FRAG_SHIFT			20
> +#define UART_STATUS_REG			0x1c
> +#define ESP32_UART_RXFIFO_CNT_MASK		0x000000ff
> +#define ESP32S3_UART_RXFIFO_CNT_MASK		0x000003ff
> +#define UART_RXFIFO_CNT_SHIFT			0
> +#define UART_DSRN_MASK				0x00002000
> +#define UART_CTSN_MASK				0x00004000
> +#define ESP32_UART_TXFIFO_CNT_MASK		0x00ff0000
> +#define ESP32S3_UART_TXFIFO_CNT_MASK		0x03ff0000
> +#define UART_TXFIFO_CNT_SHIFT			16
> +#define UART_ST_UTX_OUT_MASK			0x0f000000
> +#define UART_ST_UTX_OUT_IDLE			0x00000000
> +#define UART_ST_UTX_OUT_SHIFT			24
> +#define UART_CONF0_REG			0x20
> +#define UART_PARITY_MASK			0x00000001
> +#define UART_PARITY_EN_MASK			0x00000002
> +#define UART_BIT_NUM_MASK			0x0000000c
> +#define UART_BIT_NUM_5				0x00000000
> +#define UART_BIT_NUM_6				0x00000004
> +#define UART_BIT_NUM_7				0x00000008
> +#define UART_BIT_NUM_8				0x0000000c
> +#define UART_STOP_BIT_NUM_MASK			0x00000030
> +#define UART_STOP_BIT_NUM_1			0x00000010
> +#define UART_STOP_BIT_NUM_2			0x00000030
> +#define UART_SW_RTS_MASK			0x00000040
> +#define UART_SW_DTR_MASK			0x00000080
> +#define UART_LOOPBACK_MASK			0x00004000
> +#define UART_TX_FLOW_EN_MASK			0x00008000
> +#define UART_RTS_INV_MASK			0x00800000
> +#define UART_DTR_INV_MASK			0x01000000
> +#define ESP32_UART_TICK_REF_ALWAYS_ON_MASK	0x08000000
> +#define ESP32S3_UART_TICK_REF_ALWAYS_ON_MASK	0x00000000
> +#define UART_CONF1_REG			0x24
> +#define ESP32_UART_RXFIFO_FULL_THRHD_MASK	0x0000007f
> +#define ESP32S3_UART_RXFIFO_FULL_THRHD_MASK	0x000003ff
> +#define UART_RXFIFO_FULL_THRHD_SHIFT		0
> +#define ESP32_UART_TXFIFO_EMPTY_THRHD_MASK	0x00007f00
> +#define ESP32S3_UART_TXFIFO_EMPTY_THRHD_MASK	0x000ffc00
> +#define ESP32_UART_TXFIFO_EMPTY_THRHD_SHIFT	8
> +#define ESP32S3_UART_TXFIFO_EMPTY_THRHD_SHIFT	10
> +#define ESP32_UART_RX_FLOW_EN_MASK		0x00800000
> +#define ESP32S3_UART_RX_FLOW_EN_MASK		0x00400000
> +
> +struct esp32_port {
> +	struct uart_port port;
> +	struct clk *clk;
> +};
> +
> +struct esp32_uart_variant {
> +	u32 clkdiv_mask;
> +	u32 rxfifo_cnt_mask;
> +	u32 txfifo_cnt_mask;
> +	u32 rxfifo_full_thrhd_mask;
> +	u32 txfifo_empty_thrhd_mask;
> +	u32 txfifo_empty_thrhd_shift;
> +	u32 rx_flow_en;
> +	const char *type;
> +};
> +
> +static const struct esp32_uart_variant esp32_variant = {
> +	.clkdiv_mask = ESP32_UART_CLKDIV_MASK,
> +	.rxfifo_cnt_mask = ESP32_UART_RXFIFO_CNT_MASK,
> +	.txfifo_cnt_mask = ESP32_UART_TXFIFO_CNT_MASK,
> +	.rxfifo_full_thrhd_mask = ESP32_UART_RXFIFO_FULL_THRHD_MASK,
> +	.txfifo_empty_thrhd_mask = ESP32_UART_TXFIFO_EMPTY_THRHD_MASK,
> +	.txfifo_empty_thrhd_shift = ESP32_UART_TXFIFO_EMPTY_THRHD_SHIFT,
> +	.rx_flow_en = ESP32_UART_RX_FLOW_EN_MASK,
> +	.type = "ESP32 UART",
> +};
> +
> +static const struct esp32_uart_variant esp32s3_variant = {
> +	.clkdiv_mask = ESP32S3_UART_CLKDIV_MASK,
> +	.rxfifo_cnt_mask = ESP32S3_UART_RXFIFO_CNT_MASK,
> +	.txfifo_cnt_mask = ESP32S3_UART_TXFIFO_CNT_MASK,
> +	.rxfifo_full_thrhd_mask = ESP32S3_UART_RXFIFO_FULL_THRHD_MASK,
> +	.txfifo_empty_thrhd_mask = ESP32S3_UART_TXFIFO_EMPTY_THRHD_MASK,
> +	.txfifo_empty_thrhd_shift = ESP32S3_UART_TXFIFO_EMPTY_THRHD_SHIFT,
> +	.rx_flow_en = ESP32S3_UART_RX_FLOW_EN_MASK,
> +	.type = "ESP32S3 UART",
> +};
> +
> +static const struct of_device_id esp32_uart_dt_ids[] = {
> +	{
> +		.compatible = "esp,esp32-uart",
> +		.data = &esp32_variant,
> +	}, {
> +		.compatible = "esp,esp32s3-uart",
> +		.data = &esp32s3_variant,
> +	}, { /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, esp32_uart_dt_ids);
> +
> +static struct esp32_port *esp32_uart_ports[UART_NR];
> +
> +static const struct esp32_uart_variant *port_variant(struct uart_port *port)
> +{
> +	return port->private_data;
> +}
> +
> +static void esp32_uart_write(struct uart_port *port, unsigned long reg, u32 v)
> +{
> +	writel(v, port->membase + reg);
> +}
> +
> +static u32 esp32_uart_read(struct uart_port *port, unsigned long reg)
> +{
> +	return readl(port->membase + reg);
> +}
> +
> +static u32 esp32_uart_tx_fifo_cnt(struct uart_port *port)
> +{
> +	return (esp32_uart_read(port, UART_STATUS_REG) &
> +		port_variant(port)->txfifo_cnt_mask) >> UART_TXFIFO_CNT_SHIFT;
> +}
> +
> +static u32 esp32_uart_rx_fifo_cnt(struct uart_port *port)
> +{
> +	return (esp32_uart_read(port, UART_STATUS_REG) &
> +		port_variant(port)->rxfifo_cnt_mask) >> UART_RXFIFO_CNT_SHIFT;

FIELD_GET().

Use more lines (and a local variable) instead of splitting one line. It 
will be more readable that way.

> +}
> +
> +/* return TIOCSER_TEMT when transmitter is not busy */
> +static unsigned int esp32_uart_tx_empty(struct uart_port *port)
> +{
> +	u32 status = esp32_uart_read(port, UART_STATUS_REG) &
> +		(port_variant(port)->txfifo_cnt_mask | UART_ST_UTX_OUT_MASK);

Ditto.

> +
> +	pr_debug("%s: %08x\n", __func__, status);
> +	return status == UART_ST_UTX_OUT_IDLE ? TIOCSER_TEMT : 0;
> +}
> +
> +static void esp32_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
> +{
> +	u32 conf0 = esp32_uart_read(port, UART_CONF0_REG) &
> +		~(UART_LOOPBACK_MASK |
> +		  UART_SW_RTS_MASK | UART_RTS_INV_MASK |
> +		  UART_SW_DTR_MASK | UART_DTR_INV_MASK);

Ditto.

> +	if (mctrl & TIOCM_RTS)
> +		conf0 |= UART_SW_RTS_MASK;
> +	if (mctrl & TIOCM_DTR)
> +		conf0 |= UART_SW_DTR_MASK;
> +	if (mctrl & TIOCM_LOOP)
> +		conf0 |= UART_LOOPBACK_MASK;
> +
> +	esp32_uart_write(port, UART_CONF0_REG, conf0);
> +}
> +
> +static unsigned int esp32_uart_get_mctrl(struct uart_port *port)
> +{
> +	u32 status = esp32_uart_read(port, UART_STATUS_REG);
> +	unsigned int ret = TIOCM_CAR;
> +
> +	if (status & UART_DSRN_MASK)
> +		ret |= TIOCM_DSR;
> +	if (status & UART_CTSN_MASK)
> +		ret |= TIOCM_CTS;
> +
> +	return ret;
> +}
> +
> +static void esp32_uart_stop_tx(struct uart_port *port)
> +{
> +	u32 int_ena;
> +
> +	int_ena = esp32_uart_read(port, UART_INT_ENA_REG);

	int_ena &= ~UART_TXFIFO_EMPTY_INT_MASK;

> +	esp32_uart_write(port, UART_INT_ENA_REG,
> +			 int_ena & ~UART_TXFIFO_EMPTY_INT_MASK);

Just int_ena is enough after adding the logic op on its own line.

> +}
> +
> +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;
> +
> +		if (!rx) {
> +			brk = esp32_uart_read(port, UART_INT_ST_REG) &
> +				UART_BRK_DET_INT_MASK;
> +		}
> +		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);
> +		}
> +	}
> +	spin_unlock_irqrestore(&port->lock, flags);
> +
> +	tty_flip_buffer_push(tty_port);
> +}
> +
> +static void esp32_uart_put_char(struct uart_port *port, unsigned char c)
> +{
> +	esp32_uart_write(port, UART_FIFO_REG, c);
> +}
> +
> +static void esp32_uart_put_char_sync(struct uart_port *port, unsigned char c)
> +{
> +	while (esp32_uart_tx_fifo_cnt(port) >= ESP32_UART_TX_FIFO_SIZE)
> +		cpu_relax();
> +	esp32_uart_put_char(port, c);
> +}
> +
> +static void esp32_uart_transmit_buffer(struct uart_port *port)
> +{
> +	struct circ_buf *xmit = &port->state->xmit;
> +	u32 tx_fifo_used = esp32_uart_tx_fifo_cnt(port);
> +
> +	while (!uart_circ_empty(xmit) && tx_fifo_used < ESP32_UART_TX_FIFO_SIZE) {
> +		esp32_uart_put_char(port, xmit->buf[xmit->tail]);
> +		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
> +		port->icount.tx++;
> +		++tx_fifo_used;
> +	}
> +
> +	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
> +		uart_write_wakeup(port);

Too much open-coding here. Please use the helpers (likely the ones which 
replace the whole tx loop + its common surrounding code).


> +	if (uart_circ_empty(xmit)) {
> +		esp32_uart_stop_tx(port);
> +	} else {
> +		u32 int_ena;
> +
> +		int_ena = esp32_uart_read(port, UART_INT_ENA_REG);
> +		esp32_uart_write(port, UART_INT_ENA_REG,
> +				 int_ena | UART_TXFIFO_EMPTY_INT_MASK);

Own line for logic op.

> +	}
> +}
> +
> +static void esp32_uart_txint(struct uart_port *port)
> +{
> +	esp32_uart_transmit_buffer(port);
> +}
> +
> +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_MASK | UART_BRK_DET_INT_MASK))
> +		esp32_uart_rxint(port);
> +	if (status & UART_TXFIFO_EMPTY_INT_MASK)
> +		esp32_uart_txint(port);
> +
> +	esp32_uart_write(port, UART_INT_CLR_REG, status);
> +	return IRQ_HANDLED;
> +}
> +
> +static void esp32_uart_start_tx(struct uart_port *port)
> +{
> +	esp32_uart_transmit_buffer(port);
> +}
> +
> +static void esp32_uart_stop_rx(struct uart_port *port)
> +{
> +	u32 int_ena;
> +
> +	int_ena = esp32_uart_read(port, UART_INT_ENA_REG);
> +	esp32_uart_write(port, UART_INT_ENA_REG,
> +			 int_ena & ~UART_RXFIFO_FULL_INT_MASK);

Ditto.

> +}
> +
> +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;
> +
> +	spin_lock_irqsave(&port->lock, flags);
> +	esp32_uart_write(port, UART_CONF1_REG,
> +			 (1 << UART_RXFIFO_FULL_THRHD_SHIFT) |

Use FIELD_PREP()

> +			 (1 << port_variant(port)->txfifo_empty_thrhd_shift));
> +	esp32_uart_write(port, UART_INT_CLR_REG,
> +			 UART_RXFIFO_FULL_INT_MASK |
> +			 UART_BRK_DET_INT_MASK);

This fits to two lines (well one too, especially if you remove those 
_MASK postfixes).

> +	esp32_uart_write(port, UART_INT_ENA_REG,
> +			 UART_RXFIFO_FULL_INT_MASK |
> +			 UART_BRK_DET_INT_MASK);

Ditto.

> +	spin_unlock_irqrestore(&port->lock, flags);
> +
> +	ret = devm_request_irq(port->dev, port->irq, esp32_uart_int, 0,
> +			       DRIVER_NAME, port);
> +
> +	pr_debug("%s, request_irq: %d, conf1 = %08x, int_st = %08x, status = %08x\n",
> +		 __func__, ret,
> +		 esp32_uart_read(port, UART_CONF1_REG),
> +		 esp32_uart_read(port, UART_INT_ST_REG),
> +		 esp32_uart_read(port, UART_STATUS_REG));
> +	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);
> +	clk_disable_unprepare(sport->clk);
> +}
> +
> +static void 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 | (frag << UART_CLKDIV_FRAG_SHIFT));

FIELD_PREP(). Also div be encapsulated into FIELD_PREP here even if it's 
shift is 0.

> +	} else {
> +		dev_warn(port->dev,
> +			 "%s: %d baud is out of reach, setting %d\n",
> +			__func__, baud,

Don't print __func__.

> +			port->uartclk / port_variant(port)->clkdiv_mask);
> +		esp32_uart_write(port, UART_CLKDIV_REG,
> +				 port_variant(port)->clkdiv_mask |
> +				 UART_CLKDIV_FRAG_MASK);

I think you want to make the meaning more obvious here by using 
FIELD_MAX(UART_CLKDIV_FRAG_MASK);

> +	}
> +}
> +
> +static void esp32_uart_set_termios(struct uart_port *port,
> +				   struct ktermios *termios,
> +				   const struct ktermios *old)
> +{
> +	unsigned long flags;
> +	u32 conf0, conf1;
> +	u32 baud;
> +	const u32 rx_flow_en = port_variant(port)->rx_flow_en;
> +
> +	spin_lock_irqsave(&port->lock, flags);
> +	conf0 = esp32_uart_read(port, UART_CONF0_REG) &
> +		~(UART_PARITY_EN_MASK | UART_PARITY_MASK |
> +		  UART_BIT_NUM_MASK | UART_STOP_BIT_NUM_MASK);
> +	conf1 = esp32_uart_read(port, UART_CONF1_REG) &
> +		~rx_flow_en;

Split logic to oen lines please.

> +
> +	if (termios->c_cflag & PARENB) {
> +		conf0 |= UART_PARITY_EN_MASK;
> +		if (termios->c_cflag & PARODD)
> +			conf0 |= UART_PARITY_MASK;
> +	}
> +
> +	switch (termios->c_cflag & CSIZE) {
> +	case CS5:
> +		conf0 |= UART_BIT_NUM_5;
> +		break;
> +	case CS6:
> +		conf0 |= UART_BIT_NUM_6;
> +		break;
> +	case CS7:
> +		conf0 |= UART_BIT_NUM_7;
> +		break;
> +	case CS8:
> +		conf0 |= UART_BIT_NUM_8;
> +		break;
> +	}
> +
> +	if (termios->c_cflag & CSTOPB)
> +		conf0 |= UART_STOP_BIT_NUM_2;
> +	else
> +		conf0 |= UART_STOP_BIT_NUM_1;
> +
> +	if (termios->c_cflag & CRTSCTS)
> +		conf1 |= rx_flow_en;

If you don't support some bits, you should clear them (CMSPAR).

> +	esp32_uart_write(port, UART_CONF0_REG, conf0);
> +	esp32_uart_write(port, UART_CONF1_REG, conf1);
> +	spin_unlock_irqrestore(&port->lock, flags);
> +
> +	/*
> +	 * esp32s3 may not support 9600, passing its minimal baud rate
> +	 * as the min argument would trigger a WARN inside uart_get_baud_rate
> +	 */
> +	baud = uart_get_baud_rate(port, termios, old,
> +				  0, port->uartclk / 16);

This looks questionable solution to the problem mentioned in the comment.
What happens when user asks for baudrates below the minimum supported one?

You might need to do something touching the core code to handle the case 
where 9600 is not possible fallback.

> +	if (baud)
> +		esp32_uart_set_baud(port, baud);
> +}

set_termios() function lacks call to uart_update_timeout().

> +
> +static const char *esp32_uart_type(struct uart_port *port)
> +{
> +	return port_variant(port)->type;
> +}
> +
> +static void esp32_uart_release_port(struct uart_port *port)
> +{
> +}
> +
> +static int esp32_uart_request_port(struct uart_port *port)
> +{
> +	return 0;
> +}
> +
> +/* configure/auto-configure the port */
> +static void esp32_uart_config_port(struct uart_port *port, int flags)
> +{
> +	if (flags & UART_CONFIG_TYPE)
> +		port->type = PORT_ESP32UART;
> +}
> +
> +#ifdef CONFIG_CONSOLE_POLL
> +static int esp32_uart_poll_init(struct uart_port *port)
> +{
> +	struct esp32_port *sport = container_of(port, struct esp32_port, port);
> +
> +	return clk_prepare_enable(sport->clk);
> +}
> +
> +static void esp32_uart_poll_put_char(struct uart_port *port, unsigned char c)
> +{
> +	esp32_uart_put_char_sync(port, c);
> +}
> +
> +static int esp32_uart_poll_get_char(struct uart_port *port)
> +{
> +	if (esp32_uart_rx_fifo_cnt(port))
> +		return esp32_uart_read(port, UART_FIFO_REG);
> +	else
> +		return NO_POLL_CHAR;
> +
> +}
> +#endif
> +
> +static const struct uart_ops esp32_uart_pops = {
> +	.tx_empty	= esp32_uart_tx_empty,
> +	.set_mctrl	= esp32_uart_set_mctrl,
> +	.get_mctrl	= esp32_uart_get_mctrl,
> +	.stop_tx	= esp32_uart_stop_tx,
> +	.start_tx	= esp32_uart_start_tx,
> +	.stop_rx	= esp32_uart_stop_rx,
> +	.startup	= esp32_uart_startup,
> +	.shutdown	= esp32_uart_shutdown,
> +	.set_termios	= esp32_uart_set_termios,
> +	.type		= esp32_uart_type,
> +	.release_port	= esp32_uart_release_port,
> +	.request_port	= esp32_uart_request_port,
> +	.config_port	= esp32_uart_config_port,
> +#ifdef CONFIG_CONSOLE_POLL
> +	.poll_init	= esp32_uart_poll_init,
> +	.poll_put_char	= esp32_uart_poll_put_char,
> +	.poll_get_char	= esp32_uart_poll_get_char,
> +#endif
> +};
> +
> +static void esp32_uart_console_putchar(struct uart_port *port, unsigned char c)
> +{
> +	esp32_uart_put_char_sync(port, c);
> +}
> +
> +static void esp32_uart_string_write(struct uart_port *port, const char *s,
> +				    unsigned int count)
> +{
> +	uart_console_write(port, s, count, esp32_uart_console_putchar);
> +}
> +
> +static void
> +esp32_uart_console_write(struct console *co, const char *s, unsigned int count)
> +{
> +	struct esp32_port *sport = esp32_uart_ports[co->index];
> +	struct uart_port *port = &sport->port;
> +	unsigned long flags;
> +	int locked = 1;
> +
> +	if (port->sysrq)
> +		locked = 0;
> +	else if (oops_in_progress)
> +		locked = spin_trylock_irqsave(&port->lock, flags);
> +	else
> +		spin_lock_irqsave(&port->lock, flags);
> +
> +	esp32_uart_string_write(port, s, count);
> +
> +	if (locked)
> +		spin_unlock_irqrestore(&port->lock, flags);
> +}
> +
> +static int __init esp32_uart_console_setup(struct console *co, char *options)
> +{
> +	struct esp32_port *sport;
> +	int baud = 115200;
> +	int bits = 8;
> +	int parity = 'n';
> +	int flow = 'n';
> +	int ret;

This lacks newline after declarations.

> +	/*
> +	 * check whether an invalid uart number has been specified, and
> +	 * if so, search for the first available port that does have
> +	 * console support.
> +	 */
> +	if (co->index == -1 || co->index >= ARRAY_SIZE(esp32_uart_ports))
> +		co->index = 0;
> +
> +	sport = esp32_uart_ports[co->index];
> +	if (!sport)
> +		return -ENODEV;
> +
> +	ret = clk_prepare_enable(sport->clk);
> +	if (ret)
> +		return ret;
> +
> +	if (options)
> +		uart_parse_options(options, &baud, &parity, &bits, &flow);
> +
> +	return uart_set_options(&sport->port, co, baud, parity, bits, flow);
> +}
> +
> +static int esp32_uart_console_exit(struct console *co)
> +{
> +	struct esp32_port *sport = esp32_uart_ports[co->index];
> +
> +	clk_disable_unprepare(sport->clk);
> +	return 0;
> +}
> +
> +static struct uart_driver esp32_uart_reg;
> +static struct console esp32_uart_console = {
> +	.name		= DEV_NAME,
> +	.write		= esp32_uart_console_write,
> +	.device		= uart_console_device,
> +	.setup		= esp32_uart_console_setup,
> +	.exit		= esp32_uart_console_exit,
> +	.flags		= CON_PRINTBUFFER,
> +	.index		= -1,
> +	.data		= &esp32_uart_reg,
> +};
> +
> +static void esp32_uart_earlycon_putchar(struct uart_port *port, unsigned char c)
> +{
> +	esp32_uart_put_char_sync(port, c);
> +}
> +
> +static void esp32_uart_earlycon_write(struct console *con, const char *s,
> +				      unsigned int n)
> +{
> +	struct earlycon_device *dev = con->data;
> +
> +	uart_console_write(&dev->port, s, n, esp32_uart_earlycon_putchar);
> +}
> +
> +#ifdef CONFIG_CONSOLE_POLL
> +static int esp32_uart_earlycon_read(struct console *con, char *s, unsigned int n)
> +{
> +	struct earlycon_device *dev = con->data;
> +	int num_read = 0;
> +
> +	while (num_read < n) {
> +		int c = esp32_uart_poll_get_char(&dev->port);
> +
> +		if (c == NO_POLL_CHAR)
> +			break;
> +		s[num_read++] = c;
> +	}
> +	return num_read;
> +}
> +#endif
> +
> +static int __init esp32xx_uart_early_console_setup(struct earlycon_device *device,
> +						   const char *options)
> +{
> +	if (!device->port.membase)
> +		return -ENODEV;
> +
> +	device->con->write = esp32_uart_earlycon_write;
> +#ifdef CONFIG_CONSOLE_POLL
> +	device->con->read = esp32_uart_earlycon_read;
> +#endif
> +	if (device->port.uartclk != BASE_BAUD * 16)
> +		esp32_uart_set_baud(&device->port, device->baud);
> +
> +	return 0;
> +}
> +
> +static int __init esp32_uart_early_console_setup(struct earlycon_device *device,
> +						 const char *options)
> +{
> +	device->port.private_data = (void *)&esp32_variant;
> +	return esp32xx_uart_early_console_setup(device, options);
> +}
> +
> +OF_EARLYCON_DECLARE(esp32uart, "esp,esp32-uart",
> +		    esp32_uart_early_console_setup);
> +
> +static int __init esp32s3_uart_early_console_setup(struct earlycon_device *device,
> +						   const char *options)
> +{
> +	device->port.private_data = (void *)&esp32s3_variant;
> +	return esp32xx_uart_early_console_setup(device, options);
> +}
> +
> +OF_EARLYCON_DECLARE(esp32s3uart, "esp,esp32s3-uart",
> +		    esp32s3_uart_early_console_setup);
> +
> +static struct uart_driver esp32_uart_reg = {
> +	.owner		= THIS_MODULE,
> +	.driver_name	= DRIVER_NAME,
> +	.dev_name	= DEV_NAME,
> +	.nr		= ARRAY_SIZE(esp32_uart_ports),
> +	.cons		= &esp32_uart_console,
> +};
> +
> +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);

One line.

> +		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;
> +
> +	esp32_uart_ports[port->line] = sport;
> +
> +	platform_set_drvdata(pdev, port);
> +
> +	ret = uart_add_one_port(&esp32_uart_reg, port);
> +	return ret;
> +}
> +
> +static int esp32_uart_remove(struct platform_device *pdev)
> +{
> +	struct uart_port *port = platform_get_drvdata(pdev);
> +
> +	uart_remove_one_port(&esp32_uart_reg, port);
> +
> +	return 0;
> +}
> +
> +
> +static struct platform_driver esp32_uart_driver = {
> +	.probe		= esp32_uart_probe,
> +	.remove		= esp32_uart_remove,
> +	.driver		= {
> +		.name	= DRIVER_NAME,
> +		.of_match_table	= esp32_uart_dt_ids,
> +	},
> +};
> +
> +static int __init esp32_uart_init(void)
> +{
> +	int ret;
> +
> +	ret = uart_register_driver(&esp32_uart_reg);
> +	if (ret)
> +		return ret;
> +
> +	ret = platform_driver_register(&esp32_uart_driver);
> +	if (ret)
> +		uart_unregister_driver(&esp32_uart_reg);
> +
> +	return ret;
> +}
> +
> +static void __exit esp32_uart_exit(void)
> +{
> +	platform_driver_unregister(&esp32_uart_driver);
> +	uart_unregister_driver(&esp32_uart_reg);
> +}
> +
> +module_init(esp32_uart_init);
> +module_exit(esp32_uart_exit);
> +
> +MODULE_DESCRIPTION("Espressif ESP32 UART driver.");

Drop .

> +MODULE_AUTHOR("Max Filippov <jcmvbkbc@gmail.com>");
> +MODULE_LICENSE("GPL");
> diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h
> index add349889d0a..ff076d6be159 100644
> --- a/include/uapi/linux/serial_core.h
> +++ b/include/uapi/linux/serial_core.h
> @@ -245,4 +245,7 @@
>  /* Sunplus UART */
>  #define PORT_SUNPLUS	123
>  
> +/* Espressif ESP32 UART */
> +#define PORT_ESP32UART	124
> +
>  #endif /* _UAPILINUX_SERIAL_CORE_H */
> 

-- 
 i.