[PATCH] sound: fix hang in mpu401_uart.c

[Jon Masters <jonathan@jonmasters.org>]

From: Jon Masters <jcm@jonmasters.org>

This fixes a hang in mpu401_uart.c that can occur when the mpu401
interface is non-existent or otherwise doesn't respond to commands but
we issue IO anyway. snd_mpu401_uart_cmd now returns an error code that is
passed up the stack so that an open() will fail immediately in such cases.

Eventually discovered after wine/cxoffice would constantly cause hard
lockups on my desktop immediately after loading (emulating Windows too
well). Turned out that I'd recently moved my sound cards around and
using /dev/sequencer now talks to a sound card with a broken MPU.

Signed-off-by: Jon Masters <jcm@jonmasters.org>

diff -urN linux-2.6.16.2_orig/sound/drivers/mpu401/mpu401_uart.c linux-2.6.16.2_dev/sound/drivers/mpu401/mpu401_uart.c
--- linux-2.6.16.2_orig/sound/drivers/mpu401/mpu401_uart.c	2006-04-07 17:56:47.000000000 +0100
+++ linux-2.6.16.2_dev/sound/drivers/mpu401/mpu401_uart.c	2006-04-16 03:33:15.000000000 +0100
@@ -183,7 +183,7 @@
 
  */
 
-static void snd_mpu401_uart_cmd(struct snd_mpu401 * mpu, unsigned char cmd, int ack)
+static int snd_mpu401_uart_cmd(struct snd_mpu401 * mpu, unsigned char cmd, int ack)
 {
 	unsigned long flags;
 	int timeout, ok;
@@ -218,9 +218,12 @@
 		ok = 1;
 	}
 	spin_unlock_irqrestore(&mpu->input_lock, flags);
-	if (! ok)
+	if (ok)
+		return 0;
+	else {
 		snd_printk("cmd: 0x%x failed at 0x%lx (status = 0x%x, data = 0x%x)\n", cmd, mpu->port, mpu->read(mpu, MPU401C(mpu)), mpu->read(mpu, MPU401D(mpu)));
-	// snd_printk("cmd: 0x%x at 0x%lx (status = 0x%x, data = 0x%x)\n", cmd, mpu->port, mpu->read(mpu, MPU401C(mpu)), mpu->read(mpu, MPU401D(mpu)));
+		return 1;
+	}
 }
 
 /*
@@ -235,8 +238,12 @@
 	if (mpu->open_input && (err = mpu->open_input(mpu)) < 0)
 		return err;
 	if (! test_bit(MPU401_MODE_BIT_OUTPUT, &mpu->mode)) {
-		snd_mpu401_uart_cmd(mpu, MPU401_RESET, 1);
-		snd_mpu401_uart_cmd(mpu, MPU401_ENTER_UART, 1);
+		if ((err = snd_mpu401_uart_cmd(mpu, MPU401_RESET, 1))) {
+			return -EFAULT;
+		}
+		if ((err = snd_mpu401_uart_cmd(mpu, MPU401_ENTER_UART, 1))) {
+			return -EFAULT;
+		}
 	}
 	mpu->substream_input = substream;
 	set_bit(MPU401_MODE_BIT_INPUT, &mpu->mode);
@@ -252,8 +259,10 @@
 	if (mpu->open_output && (err = mpu->open_output(mpu)) < 0)
 		return err;
 	if (! test_bit(MPU401_MODE_BIT_INPUT, &mpu->mode)) {
-		snd_mpu401_uart_cmd(mpu, MPU401_RESET, 1);
-		snd_mpu401_uart_cmd(mpu, MPU401_ENTER_UART, 1);
+		if ((err = snd_mpu401_uart_cmd(mpu, MPU401_RESET, 1)))
+			return -EFAULT;
+		if ((err = snd_mpu401_uart_cmd(mpu, MPU401_ENTER_UART, 1)))
+			return -EFAULT;
 	}
 	mpu->substream_output = substream;
 	set_bit(MPU401_MODE_BIT_OUTPUT, &mpu->mode);
@@ -263,28 +272,34 @@
 static int snd_mpu401_uart_input_close(struct snd_rawmidi_substream *substream)
 {
 	struct snd_mpu401 *mpu;
-
+	int err = 0;
+	
 	mpu = substream->rmidi->private_data;
 	clear_bit(MPU401_MODE_BIT_INPUT, &mpu->mode);
 	mpu->substream_input = NULL;
 	if (! test_bit(MPU401_MODE_BIT_OUTPUT, &mpu->mode))
-		snd_mpu401_uart_cmd(mpu, MPU401_RESET, 0);
+		err = snd_mpu401_uart_cmd(mpu, MPU401_RESET, 0);
 	if (mpu->close_input)
 		mpu->close_input(mpu);
+	if (err)
+		return -EFAULT;
 	return 0;
 }
 
 static int snd_mpu401_uart_output_close(struct snd_rawmidi_substream *substream)
 {
 	struct snd_mpu401 *mpu;
+	int err = 0;
 
 	mpu = substream->rmidi->private_data;
 	clear_bit(MPU401_MODE_BIT_OUTPUT, &mpu->mode);
 	mpu->substream_output = NULL;
 	if (! test_bit(MPU401_MODE_BIT_INPUT, &mpu->mode))
-		snd_mpu401_uart_cmd(mpu, MPU401_RESET, 0);
+		err = snd_mpu401_uart_cmd(mpu, MPU401_RESET, 0);
 	if (mpu->close_output)
 		mpu->close_output(mpu);
+	if (err)
+		return -EFAULT;
 	return 0;
 }
 
@@ -316,6 +331,7 @@
 			snd_mpu401_uart_remove_timer(mpu, 1);
 		clear_bit(MPU401_MODE_BIT_INPUT_TRIGGER, &mpu->mode);
 	}
+
 }
 
 /*
-
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