From 4c552a5be78bd66abd59441a21fec348ee376b49 Mon Sep 17 00:00:00 2001 From: andrea merello Date: Tue, 18 Feb 2014 02:10:45 +0100 Subject: [PATCH] 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 Signed-off-by: Andrea Merello Signed-off-by: John W. Linville --- drivers/net/wireless/rtl818x/rtl8180/dev.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/net/wireless/rtl818x/rtl8180/dev.c b/drivers/net/wireless/rtl818x/rtl8180/dev.c index 1f2462e92528..45d2cc14d71c 100644 --- a/drivers/net/wireless/rtl818x/rtl8180/dev.c +++ b/drivers/net/wireless/rtl818x/rtl8180/dev.c @@ -335,6 +335,11 @@ static void rtl8180_tx(struct ieee80211_hw *dev, entry->flags2 = info->control.rates[1].idx >= 0 ? ieee80211_get_alt_retry_rate(dev, info, 0)->bitrate << 4 : 0; entry->retry_limit = info->control.rates[0].count; + + /* We must be sure that tx_flags is written last because the HW + * looks at it to check if the rest of data is valid or not + */ + wmb(); entry->flags = cpu_to_le32(tx_flags); __skb_queue_tail(&ring->queue, skb); if (ring->entries - skb_queue_len(&ring->queue) < 2) -- 2.30.2