linux-kernel - [PATCH v2 .1 28/31] cpia2_usb: don't use stack for DMA

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Date:   Tue, 11 Oct 2016 23:18:17 -0300
From:   Mauro Carvalho Chehab <mchehab@...pensource.com>
To:     Kosuke Tatsukawa <tatsu@...jp.nec.com>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        "Mauro Carvalho Chehab" <mchehab@....samsung.com>,
        Mauro Carvalho Chehab <mchehab@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        "Johannes Stezenbach" <js@...uxtv.org>,
        Jiri Kosina <jikos@...nel.org>,
        "Patrick Boettcher" <patrick.boettcher@...teo.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        "Michael Krufky" <mkrufky@...uxtv.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "jrg.otte@...il.com" <jrg.otte@...il.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Wolfram Sang <wsa-dev@...g-engineering.com>,
        Kosuke Tatsukawa <tatsu@...jp.nec.com>
Subject: [PATCH v2 .1 28/31] cpia2_usb: don't use stack for DMA

The USB control messages require DMA to work. We cannot pass
a stack-allocated buffer, as it is not warranted that the
stack would be into a DMA enabled area.

Signed-off-by: Mauro Carvalho Chehab <mchehab@....samsung.com>

-- 

v2.1: As pointed by Kosuke Tatsukawa, I forgot to replace "registers" var
to "buf" at one of the usb_control_msg() calls.

diff --git a/drivers/media/usb/cpia2/cpia2_usb.c b/drivers/media/usb/cpia2/cpia2_usb.c
index 13620cdf0599..e9100a235831 100644
--- a/drivers/media/usb/cpia2/cpia2_usb.c
+++ b/drivers/media/usb/cpia2/cpia2_usb.c
@@ -545,18 +545,30 @@ static void free_sbufs(struct camera_data *cam)
 static int write_packet(struct usb_device *udev,
 			u8 request, u8 * registers, u16 start, size_t size)
 {
+	unsigned char *buf;
+	int ret;
+
 	if (!registers || size <= 0)
 		return -EINVAL;
 
-	return usb_control_msg(udev,
+	buf = kmalloc(size, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	memcpy(buf, registers, size);
+
+	ret = usb_control_msg(udev,
 			       usb_sndctrlpipe(udev, 0),
 			       request,
 			       USB_TYPE_VENDOR | USB_RECIP_DEVICE,
 			       start,	/* value */
 			       0,	/* index */
-			       registers,	/* buffer */
+			       buf,	/* buffer */
 			       size,
 			       HZ);
+
+	kfree(buf);
+	return ret;
 }
 
 /****************************************************************************
@@ -567,18 +579,32 @@ static int write_packet(struct usb_device *udev,
 static int read_packet(struct usb_device *udev,
 		       u8 request, u8 * registers, u16 start, size_t size)
 {
+	unsigned char *buf;
+	int ret;
+
 	if (!registers || size <= 0)
 		return -EINVAL;
 
-	return usb_control_msg(udev,
+	buf = kmalloc(size, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	ret = usb_control_msg(udev,
 			       usb_rcvctrlpipe(udev, 0),
 			       request,
 			       USB_DIR_IN|USB_TYPE_VENDOR|USB_RECIP_DEVICE,
 			       start,	/* value */
 			       0,	/* index */
-			       registers,	/* buffer */
+			       buf,	/* buffer */
 			       size,
 			       HZ);
+
+	if (ret >= 0)
+		memcpy(registers, buf, size);
+
+	kfree(buf);
+
+	return ret;
 }
 
 /******************************************************************************