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

On 16/02/16 10:36, Andy Shevchenko wrote:

On Tue, Feb 16, 2016 at 12:08 PM, Vladimir Murzin
[off-list ref] wrote:

quoted

This adds support early console for MPS2 UART which can be enabled via
earlycon=mps2,0x40004000

quoted

--- 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?

In case of broken hw, yes, but I'm quite unsure how we can help to fix
it. Do you have something in mind?

quoted

+
+       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.

I've just tried with OF_ only and seems it works fine. Thanks for
pointing at it!

Cheers
Vladimir