1 files changed, 21 insertions, 1 deletions

diff --git a/drivers/net/wireless/ath9k/hw.c b/drivers/net/wireless/ath9k/hw.c
index 34474edefc9..c38a00bbce6 100644
--- a/drivers/net/wireless/ath9k/hw.c
+++ b/drivers/net/wireless/ath9k/hw.c
@@ -437,6 +437,25 @@ static void ath9k_hw_set_defaults(struct ath_hal *ah)
         }
 
         ah->ah_config.intr_mitigation = 1;
+
+        /*
+         * We need this for PCI devices only (Cardbus, PCI, miniPCI)
+         * _and_ if on non-uniprocessor systems (Multiprocessor/HT).
+         * This means we use it for all AR5416 devices, and the few
+         * minor PCI AR9280 devices out there.
+         *
+         * Serialization is required because these devices do not handle
+         * well the case of two concurrent reads/writes due to the latency
+         * involved. During one read/write another read/write can be issued
+         * on another CPU while the previous read/write may still be working
+         * on our hardware, if we hit this case the hardware poops in a loop.
+         * We prevent this by serializing reads and writes.
+         *
+         * This issue is not present on PCI-Express devices or pre-AR5416
+         * devices (legacy, 802.11abg).
+         */
+        if (num_possible_cpus() > 1)
+                ah->ah_config.serialize_regmode = SER_REG_MODE_AUTO;
 }
 
 static struct ath_hal_5416 *ath9k_hw_newstate(u16 devid,
@@ -668,7 +687,8 @@ static struct ath_hal *ath9k_hw_do_attach(u16 devid, struct ath_softc *sc,
         }
 
         if (ah->ah_config.serialize_regmode == SER_REG_MODE_AUTO) {
-                if (ah->ah_macVersion == AR_SREV_VERSION_5416_PCI) {
+                if (ah->ah_macVersion == AR_SREV_VERSION_5416_PCI ||
+                    (AR_SREV_9280(ah) && !ah->ah_isPciExpress)) {
                         ah->ah_config.serialize_regmode =
                                 SER_REG_MODE_ON;
                 } else {