linux-kernel - [PATCH v2 1/2] mfd: viperboard: allocate I/O buffer separately

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Date:	Mon, 22 Sep 2014 22:39:18 +0300
From:	Octavian Purdila <octavian.purdila@...el.com>
To:	sameo@...ux.intel.com, lee.jones@...aro.org
Cc:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	johan@...nel.org, Octavian Purdila <octavian.purdila@...el.com>
Subject: [PATCH v2 1/2] mfd: viperboard: allocate I/O buffer separately

Currently the I/O buffer is allocated part of the device status
structure, potentially sharing the same cache line with other members
in this structure.

Allocate the buffer separately, to avoid the I/O operations corrupting
the device status structure due to cache line sharing.

Compiled tested only as I don't have access to hardware.

Signed-off-by: Octavian Purdila <octavian.purdila@...el.com>
---
 drivers/mfd/viperboard.c       | 8 ++++++++
 include/linux/mfd/viperboard.h | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/mfd/viperboard.c b/drivers/mfd/viperboard.c
index e00f534..5f62f4e 100644
--- a/drivers/mfd/viperboard.c
+++ b/drivers/mfd/viperboard.c
@@ -64,6 +64,12 @@ static int vprbrd_probe(struct usb_interface *interface,
 		return -ENOMEM;
 	}
 
+	vb->buf = kzalloc(sizeof(struct vprbrd_i2c_write_msg), GFP_KERNEL);
+	if (vb->buf == NULL) {
+		ret = -ENOMEM;
+		goto error;
+	}
+
 	mutex_init(&vb->lock);
 
 	vb->usb_dev = usb_get_dev(interface_to_usbdev(interface));
@@ -105,6 +111,7 @@ static int vprbrd_probe(struct usb_interface *interface,
 error:
 	if (vb) {
 		usb_put_dev(vb->usb_dev);
+		kfree(vb->buf);
 		kfree(vb);
 	}
 
@@ -118,6 +125,7 @@ static void vprbrd_disconnect(struct usb_interface *interface)
 	mfd_remove_devices(&interface->dev);
 	usb_set_intfdata(interface, NULL);
 	usb_put_dev(vb->usb_dev);
+	kfree(vb->buf);
 	kfree(vb);
 
 	dev_dbg(&interface->dev, "disconnected\n");
diff --git a/include/linux/mfd/viperboard.h b/include/linux/mfd/viperboard.h
index 1934528..af928d0 100644
--- a/include/linux/mfd/viperboard.h
+++ b/include/linux/mfd/viperboard.h
@@ -103,7 +103,7 @@ struct vprbrd_i2c_addr_msg {
 struct vprbrd {
 	struct usb_device *usb_dev; /* the usb device for this device */
 	struct mutex lock;
-	u8 buf[sizeof(struct vprbrd_i2c_write_msg)];
+	u8 *buf;
 	struct platform_device pdev;
 };
 
-- 
1.9.1

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