linux-kernel - Re: [PATCH] tty: serial: meson: Implement earlycon support

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Date:	Sun, 7 Feb 2016 20:22:20 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	Andreas Färber <afaerber@...e.de>,
	linux-arm-kernel@...ts.infradead.org
Cc:	Carlo Caione <carlo@...one.org>, Jonathan Corbet <corbet@....net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH] tty: serial: meson: Implement earlycon support

Hi Andreas,

On 02/07/2016 12:57 PM, Andreas Färber wrote:
> Reuse the existing console write implementation for implementing
> DT-based and command-line-based earlycon support.
> 
> Signed-off-by: Andreas Färber <afaerber@...e.de>
> ---
>  Documentation/kernel-parameters.txt |  6 ++++++
>  drivers/tty/serial/meson_uart.c     | 13 +++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 602065c..90801ac 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1030,6 +1030,12 @@ Such letter suffixes can also be entirely omitted.
>  			the driver will use only 32-bit accessors to read/write
>  			the device registers.
>  
> +		meson_serial,<addr>
> +			Start an early, polled-mode console on a meson serial
> +			port at the specified address. The serial port must
> +			already be setup and configured. Options are not yet
> +			supported.
> +
>  		msm_serial,<addr>
>  			Start an early, polled-mode console on an msm serial
>  			port at the specified address. The serial port
> diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
> index b12a37b..6f89567 100644
> --- a/drivers/tty/serial/meson_uart.c
> +++ b/drivers/tty/serial/meson_uart.c
> @@ -548,6 +548,19 @@ static int __init meson_serial_console_init(void)
>  }
>  console_initcall(meson_serial_console_init);
>  
> +static int __init
> +meson_serial_early_console_setup(struct earlycon_device *device, const char *opt)
> +{
> +	if (!device->port.membase)
> +		return -ENODEV;
> +
> +	device->con->write = meson_serial_console_write;

meson_serial_console_write() is not appropriate for earlycon; it assumes the
earlycon port is the same as the driver port (it isn't).


> +	return 0;
> +}
> +EARLYCON_DECLARE(meson_serial, meson_serial_early_console_setup);
> +OF_EARLYCON_DECLARE(meson_serial, "amlogic,meson-uart",
> +		    meson_serial_early_console_setup);

With today's linux-next (or Greg's tty-next tree), it is no longer necessary to
declare separate earlycon's when you want both; OF_EARLYCON_DECLARE() declares
both a devicetree-enabled earlycon and automatically provides for a command line
earlycon of the same name.

Regards,
Peter Hurley

> +
>  #define MESON_SERIAL_CONSOLE	(&meson_serial_console)
>  #else
>  #define MESON_SERIAL_CONSOLE	NULL
>