rtl818x: Make sure the TX descriptor "valid" flag is written by last
authorandrea merello <andrea.merello@gmail.com>
Tue, 18 Feb 2014 01:10:45 +0000 (02:10 +0100)
committerJohn W. Linville <linville@tuxdriver.com>
Tue, 4 Mar 2014 18:07:52 +0000 (13:07 -0500)
commit4c552a5be78bd66abd59441a21fec348ee376b49
treecfbf800800d32c35bdf742d277dc037b99eecf27
parentf3b6a488a670f1be2666ab97e31dcfc0b1648884
rtl818x: Make sure the TX descriptor "valid" flag is written by last

The TX descriptors are consumed by the HW using DMA.
Even if in the driver code the memory write that sets the "valid"
flag appears after all other writes, the CPU may reorder writes,
causing the HW to consider as valid a not-fully-written yet
descriptor.

This may cause HW incorrect behaviour.

This can happen because (AFAIK) the HW may attempt DMA
asynchronously without waiting to be kicked by the following
register write.

This patch adds a write memory barrier to enforce writes ordering.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
drivers/net/wireless/rtl818x/rtl8180/dev.c