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SubjectRe: [PATCH] serial: mps2-uart: Initialize early console
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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@roeck-us.net>
>> ---
>> 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;
>>
>
>

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