MFC r259685:

 Plumb the cn_grab and cn_ungrab routines down into the uart
 clients. Mask RX interrupts while grabbed on the atmel serial
 driver. This UART interrupts every character. When interrupts are
 enabled at the mountroot> prompt, this means the ISR eats the
 characters. Rather than try to create a cooperative buffering system
 for the low level kernel console, instead just mask out the ISR. For
 NS8250 and decsendents this isn't needed, since interrupts only happen
 after 14 or more characters (depending on the fifo settings). Plumb
 such that these are optional so there's no change in behavior for all
 the other UART clients. ddb worked on this platform because all
 interrupts were disabled while it was running, so this problem wasn't
 noticed. The mountroot> issue has been around for a very very long
 time.

Approved by:	re@ (gjb@)

1 files changed, 16 insertions, 0 deletions

diff --git a/sys/arm/at91/uart_dev_at91usart.c b/sys/arm/at91/uart_dev_at91usart.c
index 9bc4dbf..43655b6 100644
--- a/sys/arm/at91/uart_dev_at91usart.c
+++ b/sys/arm/at91/uart_dev_at91usart.c
@@ -219,6 +219,20 @@ at91_usart_param(struct uart_bas *bas, int baudrate, int databits,
 	return (0);
 }
 
+static void
+at91_usart_grab(struct uart_bas *bas)
+{
+
+	WR4(bas, USART_IDR, USART_CSR_RXRDY);
+}
+
+static void
+at91_usart_ungrab(struct uart_bas *bas)
+{
+
+	WR4(bas, USART_IER, USART_CSR_RXRDY);
+}
+
 static struct uart_ops at91_usart_ops = {
 	.probe = at91_usart_probe,
 	.init = at91_usart_init,
@@ -226,6 +240,8 @@ static struct uart_ops at91_usart_ops = {
 	.putc = at91_usart_putc,
 	.rxready = at91_usart_rxready,
 	.getc = at91_usart_getc,
+	.grab = at91_usart_grab,
+	.ungrab = at91_usart_ungrab,
 };
 
 static int