Re: [PATCH] serial: mps2-uart: Initialize early console

[Guenter Roeck]

On 06/19/2018 02:07 AM, Vladimir Murzin wrote:
> Hi Guenter,
>
> On 19/06/18 05:54, Guenter Roeck wrote:
> > The early console code for mps2-uart assumes that the serial hardware is
> > enabled for transmit when the system boots. However, this is not the case
> > after reset. This results in a hang in mps2_early_putchar() if the serial
> > transmitter is not enabled by a boot loader or ROM monitor.
>
> I was under impression that for earlycon there is an assumption/requirement
> that the serial port must already be setup and configured. For instance, I
> see such requirement for pl011. So it looks like boot code's fault not to
> enable serial (for mps2 it needs to setup BAUDDIV as well).

Good to know. Fine with me as well; I wasn't aware that such a requirement
existed.

Guenter

> I'm not against the patch per se, but I'd like to hear if my understanding of
> earlycon requirements is correct or not.
>
> Cheers
> Vladimir
>
> > Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > ---
> >   drivers/tty/serial/mps2-uart.c | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/tty/serial/mps2-uart.c b/drivers/tty/serial/mps2-uart.c
> > index 9f8f63719126..0743a0551ce1 100644
> > --- a/drivers/tty/serial/mps2-uart.c
> > +++ b/drivers/tty/serial/mps2-uart.c
> > @@ -448,6 +448,14 @@ static struct console mps2_uart_console = {
> >   
> >   #define MPS2_SERIAL_CONSOLE (&mps2_uart_console)
> >   
> > +static void mps2_early_init(struct uart_port *port)
> > +{
> > +	u8 control = readb(port->membase + UARTn_CTRL);
> > +
> > +	control |= UARTn_CTRL_TX_ENABLE;
> > +	writeb(control, port->membase + UARTn_CTRL);
> > +}
> > +
> >   static void mps2_early_putchar(struct uart_port *port, int ch)
> >   {
> >   	while (readb(port->membase + UARTn_STATE) & UARTn_STATE_TX_FULL)
> > @@ -469,6 +477,7 @@ static int __init mps2_early_console_setup(struct earlycon_device *device,
> >   	if (!device->port.membase)
> >   		return -ENODEV;
> >   
> > +	mps2_early_init(&device->port);
> >   	device->con->write = mps2_early_write;
> >   
> >   	return 0;