linux-kernel - Re: [PATCH] serial/liteuart; Add support for earlycon

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Message-ID: <adb78be2-18a6-224d-1fa7-36b7912fa1cf@kernel.org>
Date:   Mon, 17 May 2021 10:16:43 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Stafford Horne <shorne@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Florent Kermarrec <florent@...oy-digital.fr>,
        Mateusz Holenko <mholenko@...micro.com>,
        Joel Stanley <joel@....id.au>,
        "Gabriel L . Somlo" <gsomlo@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Karol Gugala <kgugala@...micro.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-doc@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH] serial/liteuart; Add support for earlycon

On 15. 05. 21, 10:45, Stafford Horne wrote:
> Most litex boards using RISC-V soft cores us the sbi earlycon, however
> this is not available for non RISC-V litex SoC.  This patch enables
> earlycon for liteuart which is available on all Litex SoC's making
> support for earycon debugging more widely available.
> 
> Signed-off-by: Stafford Horne <shorne@...il.com>
> Cc: Florent Kermarrec <florent@...oy-digital.fr>
> Cc: Mateusz Holenko <mholenko@...micro.com>
> Cc: Joel Stanley <joel@....id.au>
> Cc: Gabriel L. Somlo <gsomlo@...il.com>
> ---
>   .../admin-guide/kernel-parameters.txt         |  5 +++
>   drivers/tty/serial/Kconfig                    |  1 +
>   drivers/tty/serial/liteuart.c                 | 31 +++++++++++++++++++
>   3 files changed, 37 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 04545725f187..2d4a43af8de2 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1084,6 +1084,11 @@
>   			the driver will use only 32-bit accessors to read/write
>   			the device registers.
>   
> +		liteuart,<addr>
> +			Start an early console on a litex serial port at the
> +			specified address. The serial port must already be
> +			setup and configured. Options are not yet supported.
> +
>   		meson,<addr>
>   			Start an early, polled-mode console on a meson serial
>   			port at the specified address. The serial port must
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index 0c4cd4a348f4..9ceffe6ab6fd 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -1531,6 +1531,7 @@ config SERIAL_LITEUART
>   	depends on OF || COMPILE_TEST
>   	depends on LITEX
>   	select SERIAL_CORE
> +	select SERIAL_EARLYCON
>   	help
>   	  This driver is for the FPGA-based LiteUART serial controller from LiteX
>   	  SoC builder.
> diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
> index 64842f3539e1..38c472487e68 100644
> --- a/drivers/tty/serial/liteuart.c
> +++ b/drivers/tty/serial/liteuart.c
> @@ -372,6 +372,37 @@ static int __init liteuart_console_init(void)
>   console_initcall(liteuart_console_init);
>   #endif /* CONFIG_SERIAL_LITEUART_CONSOLE */
>   
> +#ifdef CONFIG_SERIAL_EARLYCON
> +static void early_liteuart_putc(struct uart_port *port, int c)
> +{
> +	while (litex_read8(port->membase + OFF_TXFULL))
> +		cpu_relax();
> +
> +	litex_write8(port->membase + OFF_RXTX, c);

Hi,

am I missing something or this doesn't differ to liteuart_putchar?

> +}
> +
> +static void early_liteuart_write(struct console *console, const char *s,
> +				    unsigned int count)
> +{
> +	struct earlycon_device *device = console->data;
> +	struct uart_port *port = &device->port;
> +
> +	uart_console_write(port, s, count, early_liteuart_putc);
> +}
> +
> +static int __init early_liteuart_setup(struct earlycon_device *device,
> +				       const char *options)
> +{
> +	if (!device->port.membase)
> +		return -ENODEV;
> +
> +	device->con->write = early_liteuart_write;
> +	return 0;
> +}
> +
> +OF_EARLYCON_DECLARE(liteuart, "litex,liteuart", early_liteuart_setup);
> +#endif /* CONFIG_SERIAL_EARLYCON */
> +
>   static int __init liteuart_init(void)
>   {
>   	int res;
> 


-- 
js
suse labs