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serial: 8250_early: Support kgdboc_earlycon

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Implement the read() function in the early console driver.  With
recent kgdb patches this allows you to use kgdb to debug fairly early
into the system boot.

We only bother implementing this if polling is enabled since kgdb
can't be enabled without that.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20200507130644.v4.11.I8f668556c244776523320a95b09373a86eda11b7@changeid
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
This commit is contained in:
Douglas Anderson
2020-05-07 13:08:49 -07:00
committed by Daniel Thompson
parent 205b5bdda2
commit c5e7467d92
1 changed files with 23 additions and 0 deletions
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23
drivers/tty/serial/8250/8250_early.c
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@ -109,6 +109,28 @@ static void early_serial8250_write(struct console *console,
uart_console_write(port, s, count, serial_putc);
}
#ifdef CONFIG_CONSOLE_POLL
static int early_serial8250_read(struct console *console,
char *s, unsigned int count)
{
struct earlycon_device *device = console->data;
struct uart_port *port = &device->port;
unsigned int status;
int num_read = 0;
while (num_read < count) {
status = serial8250_early_in(port, UART_LSR);
if (!(status & UART_LSR_DR))
break;
s[num_read++] = serial8250_early_in(port, UART_RX);
}
return num_read;
}
#else
#define early_serial8250_read NULL
#endif
static void __init init_port(struct earlycon_device *device)
{
struct uart_port *port = &device->port;
@ -149,6 +171,7 @@ int __init early_serial8250_setup(struct earlycon_device *device,
init_port(device);
device->con->write = early_serial8250_write;
device->con->read = early_serial8250_read;
return 0;
}
EARLYCON_DECLARE(uart8250, early_serial8250_setup);