[PATCH RFC 4/9] serial: serial_meson: add minimal non-DM driver

[Neil Armstrong]

On 07/09/2025 16:36, Ferass El Hafidi wrote:
> It is very limited and minimal, only implements putc/puts.
> This minimal driver is intended to be used in SPL, and other
> size-constrained situations.
> 
> Signed-off-by: Ferass El Hafidi <funderscore at postmarketos.org>
> ---
>   drivers/serial/serial.c       |   2 +
>   drivers/serial/serial_meson.c | 112 +++++++++++++++++++++++++++++++++++++++++-
>   2 files changed, 113 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c
> index e10ca6eef768502ea32bf39a41ae2e3ccd168c66..c0b1eb3056181b95e1861f1ce08fcd82ff81eb71 100644
> --- a/drivers/serial/serial.c
> +++ b/drivers/serial/serial.c
> @@ -129,6 +129,7 @@ serial_initfunc(pxa_serial_initialize);
>   serial_initfunc(smh_serial_initialize);
>   serial_initfunc(sh_serial_initialize);
>   serial_initfunc(mtk_serial_initialize);
> +serial_initfunc(meson_serial_initialize);
>   
>   /**
>    * serial_register() - Register serial driver with serial driver core
> @@ -167,6 +168,7 @@ int serial_initialize(void)
>   	smh_serial_initialize();
>   	sh_serial_initialize();
>   	mtk_serial_initialize();
> +	meson_serial_initialize();
>   
>   	serial_assign(default_serial_console()->name);
>   
> diff --git a/drivers/serial/serial_meson.c b/drivers/serial/serial_meson.c
> index bb79b9729579a661084425d6b3c5357da31dc3c0..981ea5e159062b7d13885325e17b833145281158 100644
> --- a/drivers/serial/serial_meson.c
> +++ b/drivers/serial/serial_meson.c
> @@ -3,9 +3,11 @@
>    * (C) Copyright 2016 Beniamino Galvani <b.galvani at gmail.com>
>    */
>   
> +#if CONFIG_IS_ENABLED(DM_SERIAL)
>   #include <dm.h>
> -#include <errno.h>
>   #include <fdtdec.h>
> +#endif
> +#include <errno.h>
>   #include <linux/kernel.h>
>   #include <linux/bitops.h>
>   #include <linux/compiler.h>
> @@ -51,6 +53,7 @@ struct meson_serial_plat {
>   #define AML_UART_REG5_USE_NEW_BAUD	BIT(23) /* default 1 (use new baud rate register) */
>   #define AML_UART_REG5_BAUD_MASK		0x7fffff
>   
> +#if CONFIG_IS_ENABLED(DM_SERIAL)
>   static u32 meson_calc_baud_divisor(ulong src_rate, u32 baud)
>   {
>   	/*
> @@ -245,6 +248,113 @@ U_BOOT_DRIVER(serial_meson) = {
>   	.plat_auto	= sizeof(struct meson_serial_plat),
>   };
>   
> +DM_DRIVER_ALIAS(serial_meson, amlogic_meson_gx_uart);

Why is this needed ?

> +
> +#else
> +
> +static int meson_serial_init(void)
> +{
> +	struct meson_uart *const uart = (struct meson_uart *)CONFIG_VAL(DEBUG_UART_BASE);
> +	u32 val;
> +
> +	val = readl(&uart->control);
> +	val |= (AML_UART_RX_RST | AML_UART_TX_RST | AML_UART_CLR_ERR);
> +	writel(val, &uart->control);
> +	val &= ~(AML_UART_RX_RST | AML_UART_TX_RST | AML_UART_CLR_ERR);
> +	writel(val, &uart->control);
> +	val |= (AML_UART_RX_EN | AML_UART_TX_EN);
> +	writel(val, &uart->control);
> +
> +	return 0;
> +}
> +
> +static int meson_serial_stop(void)
> +{
> +	return 0;
> +}
> +
> +static void meson_serial_setbrg(void)
> +{
> +}
> +
> +static void meson_serial_putc(const char ch)
> +{
> +	struct meson_uart *uart = (struct meson_uart *)CONFIG_VAL(DEBUG_UART_BASE);
> +
> +	/* On '\n' also do '\r' */
> +	if (ch == '\n')
> +		meson_serial_putc('\r');
> +
> +	while (readl(&uart->status) & AML_UART_TX_FULL)
> +		;
> +
> +	writel(ch, &uart->wfifo);
> +}
> +
> +static void meson_serial_puts(const char *s)
> +{
> +	while (*s)
> +		meson_serial_putc(*s++);
> +}
> +
> +static int meson_serial_getc(void)
> +{
> +	struct meson_uart *const uart = (struct meson_uart *)CONFIG_VAL(DEBUG_UART_BASE);
> +	uint32_t status = readl(&uart->status);
> +
> +	if (status & AML_UART_RX_EMPTY)
> +		return -EAGAIN;
> +
> +	if (status & AML_UART_ERR) {
> +		u32 val = readl(&uart->control);
> +
> +		/* Clear error */
> +		val |= AML_UART_CLR_ERR;
> +		writel(val, &uart->control);
> +		val &= ~AML_UART_CLR_ERR;
> +		writel(val, &uart->control);
> +
> +		/* Remove spurious byte from fifo */
> +		readl(&uart->rfifo);
> +		return -EIO;
> +	}
> +
> +	return readl(&uart->rfifo) & 0xff;
> +}
> +
> +static int meson_serial_tstc(void)
> +{
> +	struct meson_uart *const uart = (struct meson_uart *)CONFIG_VAL(DEBUG_UART_BASE);
> +	uint32_t status = readl(&uart->status);
> +
> +	if (status & AML_UART_RX_EMPTY)
> +		return 0;
> +	return 1;
> +}
> +
> +struct serial_device meson_serial_device = {
> +	.name	= "meson_serial",
> +	.start	= meson_serial_init,
> +	.stop	= meson_serial_stop,
> +	.setbrg	= meson_serial_setbrg,
> +	.getc	= meson_serial_getc,
> +	.tstc	= meson_serial_tstc,
> +	.putc	= meson_serial_putc,
> +	.puts	= meson_serial_puts,
> +};
> +
> +void meson_serial_initialize(void)
> +{
> +	serial_register(&meson_serial_device);
> +}
> +
> +__weak struct serial_device *default_serial_console(void)
> +{
> +	return &meson_serial_device;
> +}
> +
> +#endif
> +
>   #ifdef CONFIG_DEBUG_UART_MESON
>   
>   #include <debug_uart.h>
>