applespi: Drain outstading spi commands before removing module.

This ensures our callbacks are not called after we've been removed, and
it also ensures that writes have been fully processed (including the
associated response being received), thereby resolving occasional errors
when removing and re-inserting this module.

applespi.c

@@ -30,6 +30,7 @@
 #include <linux/crc16.h>
 #include <linux/version.h>
 #include <linux/workqueue.h>
+#include <linux/wait.h>
 #include <linux/notifier.h>
 #include <linux/leds.h>
 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
@@ -231,6 +232,11 @@ struct applespi_data {
 	unsigned			cmd_log_mask;
 
 	struct led_classdev		backlight_info;
+
+	bool				drain;
+	wait_queue_head_t		drain_complete;
+	bool				read_active;
+	bool				write_active;
 };
 
 static const unsigned char applespi_scancodes[] = {
@@ -557,6 +563,7 @@ static int applespi_setup_spi(struct applespi_data *applespi)
 		return sts;
 
 	spin_lock_init(&applespi->cmd_msg_lock);
+	init_waitqueue_head(&applespi->drain_complete);
 
 	return 0;
 }
@@ -624,6 +631,10 @@ applespi_send_cmd_msg(struct applespi_data *applespi)
 	u16 crc;
 	int sts;
 
+	/* check if draining */
+	if (applespi->drain)
+		return 0;
+
 	/* check whether send is in progress */
 	if (applespi->cmd_msg_queued)
 		return 0;
@@ -696,10 +707,13 @@ applespi_send_cmd_msg(struct applespi_data *applespi)
 	sts = applespi_async(applespi, &applespi->wr_m,
 			     applespi_async_write_complete);
 
-	if (sts != 0)
+	if (sts != 0) {
 		pr_warn("Error queueing async write to device: %d\n", sts);
-	else
+	} else {
 		applespi->cmd_msg_queued = true;
+		applespi->write_active = true;
+	}
+
 
 	return sts;
 }
@@ -969,6 +983,7 @@ static void
 applespi_got_data(struct applespi_data *applespi)
 {
 	struct keyboard_protocol *keyboard_protocol;
+	unsigned long flags;
 
 	keyboard_protocol = (struct keyboard_protocol*) applespi->rx_buffer;
 	if (keyboard_protocol->packet_type == PACKET_TYPE_READ &&
@@ -1010,6 +1025,19 @@ applespi_got_data(struct applespi_data *applespi)
 	 */
 	udelay(SPI_RW_CHG_DLY);
 
+	/* handle draining */
+	spin_lock_irqsave(&applespi->cmd_msg_lock, flags);
+
+	applespi->read_active = false;
+	if (keyboard_protocol->packet_type == PACKET_TYPE_WRITE)
+		applespi->write_active = false;
+
+	if (applespi->drain && !applespi->write_active)
+		wake_up_all(&applespi->drain_complete);
+
+	spin_unlock_irqrestore(&applespi->cmd_msg_lock, flags);
+
+	/* notify write complete */
 	if (keyboard_protocol->packet_type == PACKET_TYPE_WRITE)
 		applespi_cmd_msg_complete(applespi);
 }
@@ -1029,6 +1057,7 @@ static void applespi_async_read_complete(void *context)
 static u32 applespi_notify(acpi_handle gpe_device, u32 gpe, void *context)
 {
 	struct applespi_data *applespi = context;
+	int sts;
 	unsigned long flags;
 
 	debug_print(DBG_RD_IRQ, "--- %s ---------------------------\n",
@@ -1038,7 +1067,13 @@ static u32 applespi_notify(acpi_handle gpe_device, u32 gpe, void *context)
 	applespi_setup_spi_message(&applespi->rd_m, 2, &applespi->dl_t, &applespi->rd_t);
 
 	spin_lock_irqsave(&applespi->cmd_msg_lock, flags);
-	applespi_async(applespi, &applespi->rd_m, applespi_async_read_complete);
+
+	sts = applespi_async(applespi, &applespi->rd_m, applespi_async_read_complete);
+	if (sts != 0)
+		pr_warn("Error queueing async read to device: %d\n", sts);
+	else
+		applespi->read_active = true;
+
 	spin_unlock_irqrestore(&applespi->cmd_msg_lock, flags);
 
 	return ACPI_INTERRUPT_HANDLED;
@@ -1236,10 +1271,30 @@ static int applespi_probe(struct spi_device *spi)
 static int applespi_remove(struct spi_device *spi)
 {
 	struct applespi_data *applespi = spi_get_drvdata(spi);
+	unsigned long flags;
+
+	/* wait for all outstanding writes to finish */
+	spin_lock_irqsave(&applespi->cmd_msg_lock, flags);
+
+	applespi->drain = true;
+	wait_event_lock_irq(applespi->drain_complete, !applespi->write_active,
+			    applespi->cmd_msg_lock);
 
+	spin_unlock_irqrestore(&applespi->cmd_msg_lock, flags);
+
+	/* shut things down */
 	acpi_disable_gpe(NULL, applespi->gpe);
 	acpi_remove_gpe_handler(NULL, applespi->gpe, applespi_notify);
 
+	/* wait for all outstanding reads to finish */
+	spin_lock_irqsave(&applespi->cmd_msg_lock, flags);
+
+	wait_event_lock_irq(applespi->drain_complete, !applespi->read_active,
+			    applespi->cmd_msg_lock);
+
+	spin_unlock_irqrestore(&applespi->cmd_msg_lock, flags);
+
+	/* done */
 	pr_info("spi-device remove done: %s\n", dev_name(&spi->dev));
 	return 0;
 }