linux-kernel - Re: [PATCH v3 05/10] serial: mps2-uart: add support for early console

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Date:	Tue, 16 Feb 2016 12:36:09 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Vladimir Murzin <vladimir.murzin@....com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Russell King <linux@....linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	"ijc+devicetree" <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, Jiri Slaby <jslaby@...e.cz>,
	Rob Herring <robh+dt@...nel.org>,
	devicetree <devicetree@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 05/10] serial: mps2-uart: add support for early console

On Tue, Feb 16, 2016 at 12:08 PM, Vladimir Murzin
<vladimir.murzin@....com> wrote:
> This adds support early console for MPS2 UART which can be enabled via
> earlycon=mps2,0x40004000


> --- a/drivers/tty/serial/mps2-uart.c
> +++ b/drivers/tty/serial/mps2-uart.c
> @@ -435,6 +435,36 @@ static struct console mps2_uart_console = {
>
>  #define MPS2_SERIAL_CONSOLE (&mps2_uart_console)
>
> +static void mps2_early_putchar(struct uart_port *port, int ch)
> +{
> +
> +       while (readb(port->membase + UARTn_STATE) & UARTn_STATE_TX_FULL)
> +               cpu_relax();

Infinite busy loop?

> +
> +       writeb((unsigned char)ch, port->membase + UARTn_DATA);
> +}
> +
> +
> +static void mps2_early_write(struct console *con, const char *s, unsigned n)
> +{
> +       struct earlycon_device *dev = con->data;
> +
> +       uart_console_write(&dev->port, s, n, mps2_early_putchar);
> +}
> +
> +static int __init mps2_early_console_setup(struct earlycon_device *device,
> +                                          const char *opt)
> +{
> +       if (!device->port.membase)
> +               return -ENODEV;
> +
> +       device->con->write = mps2_early_write;
> +
> +       return 0;
> +}
> +EARLYCON_DECLARE(mps2, mps2_early_console_setup);
> +OF_EARLYCON_DECLARE(mps2, "arm,mps2-uart", mps2_early_console_setup);

IIRC Peter Hurley mentioned you don't need to put both anymore, OF_
one is enough.

-- 
With Best Regards,
Andy Shevchenko