iwlwifi: disable the buggy chain extension feature in HW

This feature has been reported to be buggy and enabled by
default. We therefore need to disable it manually.

Cc: stable@vger.kernel.org
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

2 files changed, 6 insertions, 0 deletions

diff --git a/drivers/net/wireless/iwlwifi/iwl-prph.h b/drivers/net/wireless/iwlwifi/iwl-prph.h
index 3b1069290fa9..dfd54662e3e6 100644
--- a/drivers/net/wireless/iwlwifi/iwl-prph.h
+++ b/drivers/net/wireless/iwlwifi/iwl-prph.h
@@ -224,6 +224,7 @@
 #define SCD_TXFACT              (SCD_BASE + 0x10)
 #define SCD_ACTIVE              (SCD_BASE + 0x14)
 #define SCD_QUEUECHAIN_SEL      (SCD_BASE + 0xe8)
+#define SCD_CHAINEXT_EN         (SCD_BASE + 0x244)
 #define SCD_AGGR_SEL            (SCD_BASE + 0x248)
 #define SCD_INTERRUPT_MASK      (SCD_BASE + 0x108)
 
diff --git a/drivers/net/wireless/iwlwifi/iwl-trans-pcie.c b/drivers/net/wireless/iwlwifi/iwl-trans-pcie.c
index ec6fb395b84d..79c6b91417f9 100644
--- a/drivers/net/wireless/iwlwifi/iwl-trans-pcie.c
+++ b/drivers/net/wireless/iwlwifi/iwl-trans-pcie.c
@@ -1058,6 +1058,11 @@ static void iwl_tx_start(struct iwl_trans *trans)
         iwl_write_prph(trans, SCD_DRAM_BASE_ADDR,
                        trans_pcie->scd_bc_tbls.dma >> 10);
 
+        /* The chain extension of the SCD doesn't work well. This feature is
+         * enabled by default by the HW, so we need to disable it manually.
+         */
+        iwl_write_prph(trans, SCD_CHAINEXT_EN, 0);
+
         /* Enable DMA channel */
         for (chan = 0; chan < FH_TCSR_CHNL_NUM ; chan++)
                 iwl_write_direct32(trans, FH_TCSR_CHNL_TX_CONFIG_REG(chan),