rt2x00: Fix race condition when using inderect registers

Indirect registers require multiple calls to the CSR
register in order to access the indirect registers.
This must be protected under a lock to prevent race
conditions which could cause invalid data to
be returned when reading from the indirect register or silent
failures when writing data to the indirect register.

USB drivers where already protected under a mutex,
so rename the mutex and make PCI drivers use the mutex
as well.
This now means that BBP and RF registers are no longer
accessible in interrupt context. That is not a bad
situation since the slow behavior of accessing
those registers means we don't _want_ to access them
in interrupt context either.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 9 insertions, 10 deletions

diff --git a/drivers/net/wireless/rt2x00/rt2x00.h b/drivers/net/wireless/rt2x00/rt2x00.h
index baccea7184b5..fee61bee1e7e 100644
--- a/drivers/net/wireless/rt2x00/rt2x00.h
+++ b/drivers/net/wireless/rt2x00/rt2x00.h
@@ -746,16 +746,15 @@ struct rt2x00_dev {
 	} csr;
 
 	/*
-	 * Mutex to protect register accesses on USB devices.
-	 * There are 2 reasons this is needed, one is to ensure
-	 * use of the csr_cache (for USB devices) by one thread
-	 * isn't corrupted by another thread trying to access it.
-	 * The other is that access to BBP and RF registers
-	 * require multiple BUS transactions and if another thread
-	 * attempted to access one of those registers at the same
-	 * time one of the writes could silently fail.
-	 */
-	struct mutex usb_cache_mutex;
+	 * Mutex to protect register accesses.
+	 * For PCI and USB devices it protects against concurrent indirect
+	 * register access (BBP, RF, MCU) since accessing those
+	 * registers require multiple calls to the CSR registers.
+	 * For USB devices it also protects the csr_cache since that
+	 * field is used for normal CSR access and it cannot support
+	 * multiple callers simultaneously.
+	 */
+	struct mutex csr_mutex;
 
 	/*
 	 * Current packet filter configuration for the device.