linux-kernel - [PATCH 04/12] tty/serial/core: Introduce poll

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Date:	Mon, 20 Aug 2012 07:47:22 -0700
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Russell King <linux@....linux.org.uk>,
	Jason Wessel <jason.wessel@...driver.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...ux.intel.com>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Colin Cross <ccross@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com, kgdb-bugreport@...ts.sourceforge.net
Subject: [PATCH 04/12] tty/serial/core: Introduce poll_init callback

It was noticed that polling drivers (like KGDB) are not able to use
serial ports if the ports were not previously initialized via console.
I.e.  when booting with console=ttyAMA0 kgdboc=ttyAMA0, everything works
fine, but with console=ttyFOO kgdboc=ttyAMA0, the kgdboc doesn't work.

This is because we don't initialize the hardware. Calling ->startup() is
not an option, because drivers request interrupts there, and drivers
fail to handle situations when tty isn't opened with interrupts enabled.

So, we have to implement a new callback (actually, tty_ops already have
a similar callback), which does everything needed to initialize just the
hardware.

Signed-off-by: Anton Vorontsov <anton.vorontsov@...aro.org>
---
 drivers/tty/serial/serial_core.c | 15 +++++++++++++++
 include/linux/serial_core.h      |  1 +
 2 files changed, 16 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index a21dc8e..cba8443 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2108,11 +2108,13 @@ static int uart_poll_init(struct tty_driver *driver, int line, char *options)
 {
 	struct uart_driver *drv = driver->driver_state;
 	struct uart_state *state = drv->state + line;
+	struct tty_port *tport;
 	struct uart_port *port;
 	int baud = 9600;
 	int bits = 8;
 	int parity = 'n';
 	int flow = 'n';
+	int ret;
 
 	if (!state || !state->uart_port)
 		return -1;
@@ -2121,6 +2123,19 @@ static int uart_poll_init(struct tty_driver *driver, int line, char *options)
 	if (!(port->ops->poll_get_char && port->ops->poll_put_char))
 		return -1;
 
+	tport = &state->port;
+	if (!(tport->flags & ASYNC_INITIALIZED) && port->ops->poll_init) {
+		mutex_lock(&tport->mutex);
+		ret = port->ops->poll_init(port);
+		/*
+		 * We don't set ASYNCB_INITIALIZED as we only initialized the
+		 * hw, e.g. state->xmit is still uninitialized.
+		 */
+		mutex_unlock(&tport->mutex);
+		if (ret)
+			return ret;
+	}
+
 	if (options) {
 		uart_parse_options(options, &baud, &parity, &bits, &flow);
 		return uart_set_options(port, NULL, baud, parity, bits, flow);
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 0253c20..3642710 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -274,6 +274,7 @@ struct uart_ops {
 	int		(*verify_port)(struct uart_port *, struct serial_struct *);
 	int		(*ioctl)(struct uart_port *, unsigned int, unsigned long);
 #ifdef CONFIG_CONSOLE_POLL
+	int		(*poll_init)(struct uart_port *);
 	void	(*poll_put_char)(struct uart_port *, unsigned char);
 	int		(*poll_get_char)(struct uart_port *);
 #endif
-- 
1.7.11.5

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