Patch "tty: nozomi: avoid a harmless gcc warning" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

tty: nozomi: avoid a harmless gcc warning

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tty-nozomi-avoid-a-harmless-gcc-warning.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Arnd Bergmann <[email protected]>
Date: Mon, 25 Jan 2016 22:54:56 +0100
Subject: tty: nozomi: avoid a harmless gcc warning

From: Arnd Bergmann <[email protected]>

commit a4f642a8a3c2838ad09fe8313d45db46600e1478 upstream.

The nozomi wireless data driver has its own helper function to transfer data from a FIFO, doing an extra byte swap on big-endian architectures, presumably to bring the data back into byte-serial order after readw() or readl() perform their implicit byteswap.

This helper function is used in the receive_data() function to first read the length into a 32-bit variable, which causes a compile-time warning:

drivers/tty/nozomi.c: In function 'receive_data':
drivers/tty/nozomi.c:857:9: warning: 'size' may be used uninitialized in this function [-Wmaybe-uninitialized]

The problem is that gcc is unsure whether the data was actually read or not. We know that it is at this point, so we can replace it with a single readl() to shut up that warning.

I am leaving the byteswap in there, to preserve the existing behavior, even though this seems fishy: Reading the length of the data into a cpu-endian variable should normally not use a second byteswap on big-endian systems, unless the hardware is aware of the CPU endianess.

There appears to be a lot more confusion about endianess in this driver, so it probably has not worked on big-endian systems in a long time, if ever, and I have no way to test it. It's well possible that this driver has not been used by anyone in a while, the last patch that looks like it was tested on the hardware is from 2008.

---
 drivers/tty/nozomi.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -823,7 +823,7 @@ static int receive_data(enum port_type i
 	struct tty_struct *tty = tty_port_tty_get(&port->port);
 	int i, ret;
 
-	read_mem32((u32 *) &size, addr, 4);
+	size = __le32_to_cpu(readl(addr));
 	/*  DBG1( "%d bytes port: %d", size, index); */
 
 	if (tty && test_bit(TTY_THROTTLED, &tty->flags)) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/tty-nozomi-avoid-a-harmless-gcc-warning.patch queue-4.4/gfs2-avoid-uninitialized-variable-warning.patch queue-4.4/hostap-avoid-uninitialized-variable-use-in-hfa384x_get_rid.patch