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Date:   Sat, 2 Dec 2017 15:51:34 +0000
From:   alexander.levin@...izon.com
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        alexander.levin@...izon.com
Subject: [PATCH AUTOSEL for 4.14 42/64] mailbox: mailbox-test: don't rely on
 rx_buffer content to signal data ready

From: Sudeep Holla <sudeep.holla@....com>

[ Upstream commit e339c80af95e14de3712d69ddea09a3868fa14cd ]

Currently we rely on the first byte of the Rx buffer to check if there's
any data available to be read. If the first byte of the received buffer
is zero (i.e. null character), then we fail to signal that data is
available even when it's available.

Instead introduce a boolean variable to track the data availability and
update it in the channel receive callback as ready and clear it when the
data is read.

Signed-off-by: Sudeep Holla <sudeep.holla@....com>
Signed-off-by: Jassi Brar <jaswinder.singh@...aro.org>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
---
 drivers/mailbox/mailbox-test.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/mailbox/mailbox-test.c b/drivers/mailbox/mailbox-test.c
index 97fb956bb6e0..93f3d4d61fa7 100644
--- a/drivers/mailbox/mailbox-test.c
+++ b/drivers/mailbox/mailbox-test.c
@@ -30,6 +30,7 @@
 #define MBOX_HEXDUMP_MAX_LEN	(MBOX_HEXDUMP_LINE_LEN *		\
 				 (MBOX_MAX_MSG_LEN / MBOX_BYTES_PER_LINE))
 
+static bool mbox_data_ready;
 static struct dentry *root_debugfs_dir;
 
 struct mbox_test_device {
@@ -152,16 +153,14 @@ out:
 
 static bool mbox_test_message_data_ready(struct mbox_test_device *tdev)
 {
-	unsigned char data;
+	bool data_ready;
 	unsigned long flags;
 
 	spin_lock_irqsave(&tdev->lock, flags);
-	data = tdev->rx_buffer[0];
+	data_ready = mbox_data_ready;
 	spin_unlock_irqrestore(&tdev->lock, flags);
 
-	if (data != '\0')
-		return true;
-	return false;
+	return data_ready;
 }
 
 static ssize_t mbox_test_message_read(struct file *filp, char __user *userbuf,
@@ -223,6 +222,7 @@ static ssize_t mbox_test_message_read(struct file *filp, char __user *userbuf,
 	*(touser + l) = '\0';
 
 	memset(tdev->rx_buffer, 0, MBOX_MAX_MSG_LEN);
+	mbox_data_ready = false;
 
 	spin_unlock_irqrestore(&tdev->lock, flags);
 
@@ -292,6 +292,7 @@ static void mbox_test_receive_message(struct mbox_client *client, void *message)
 				     message, MBOX_MAX_MSG_LEN);
 		memcpy(tdev->rx_buffer, message, MBOX_MAX_MSG_LEN);
 	}
+	mbox_data_ready = true;
 	spin_unlock_irqrestore(&tdev->lock, flags);
 
 	wake_up_interruptible(&tdev->waitq);
-- 
2.11.0

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