From f83ed22cb62fd8e1b665924e673e01e586ee204f Mon Sep 17 00:00:00 2001
From: Warner Losh <imp@FreeBSD.org>
Date: Sat, 21 Dec 2013 16:23:31 +0000
Subject: [PATCH] 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.

MFC after:	3 days
---
 sys/arm/at91/uart_dev_at91usart.c | 16 ++++++++++++++++
 sys/dev/uart/uart_cpu.h           | 23 +++++++++++++++++++++++
 sys/dev/uart/uart_tty.c           |  4 ++++
 3 files changed, 43 insertions(+)

diff --git a/sys/arm/at91/uart_dev_at91usart.c b/sys/arm/at91/uart_dev_at91usart.c
index 9bc4dbf55b2..43655b6e6cd 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
diff --git a/sys/dev/uart/uart_cpu.h b/sys/dev/uart/uart_cpu.h
index db64d497e59..99ced1a2c0c 100644
--- a/sys/dev/uart/uart_cpu.h
+++ b/sys/dev/uart/uart_cpu.h
@@ -43,6 +43,8 @@ struct uart_ops {
 	void (*putc)(struct uart_bas *, int);
 	int (*rxready)(struct uart_bas *);
 	int (*getc)(struct uart_bas *, struct mtx *);
+	void (*grab)(struct uart_bas *);
+	void (*ungrab)(struct uart_bas *);
 };
 
 extern bus_space_tag_t uart_bus_space_io;
@@ -135,6 +137,27 @@ uart_putc(struct uart_devinfo *di, int c)
 	uart_unlock(di->hwmtx);
 }
 
+static __inline void
+uart_grab(struct uart_devinfo *di)
+{
+
+	uart_lock(di->hwmtx);
+	if (di->ops->grab)
+		di->ops->grab(&di->bas);
+	uart_unlock(di->hwmtx);
+}
+
+static __inline void
+uart_ungrab(struct uart_devinfo *di)
+{
+
+	uart_lock(di->hwmtx);
+	if (di->ops->ungrab)
+		di->ops->ungrab(&di->bas);
+	uart_unlock(di->hwmtx);
+}
+
+
 static __inline int
 uart_rxready(struct uart_devinfo *di)
 {
diff --git a/sys/dev/uart/uart_tty.c b/sys/dev/uart/uart_tty.c
index 97ee08d253b..56f879b75a3 100644
--- a/sys/dev/uart/uart_tty.c
+++ b/sys/dev/uart/uart_tty.c
@@ -112,11 +112,15 @@ uart_cnterm(struct consdev *cp)
 static void
 uart_cngrab(struct consdev *cp)
 {
+
+	uart_grab(cp->cn_arg);
 }
 
 static void
 uart_cnungrab(struct consdev *cp)
 {
+
+	uart_ungrab(cp->cn_arg);
 }
 
 static void