[PATCH] p54: avoid accessing the data mapped to streaming DMA

[Jia-Ju Bai]

In p54p_tx(), skb->data is mapped to streaming DMA on line 337:
  mapping = pci_map_single(..., skb->data, ...);

Then skb->data is accessed on line 349:
  desc->device_addr = ((struct p54_hdr *)skb->data)->req_id;

This access may cause data inconsistency between CPU cache and hardware.

To fix this problem, ((struct p54_hdr *)skb->data)->req_id is stored in
a local variable before DMA mapping, and then the driver accesses this
local variable instead of skb->data.

Signed-off-by: Jia-Ju Bai <baiji...@tsinghua.edu.cn>
---
 drivers/net/wireless/intersil/p54/p54pci.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/intersil/p54/p54pci.c 
b/drivers/net/wireless/intersil/p54/p54pci.c
index 80ad0b7eaef4..f8c6027cab6b 100644
--- a/drivers/net/wireless/intersil/p54/p54pci.c
+++ b/drivers/net/wireless/intersil/p54/p54pci.c
@@ -329,10 +329,12 @@ static void p54p_tx(struct ieee80211_hw *dev, struct 
sk_buff *skb)
        struct p54p_desc *desc;
        dma_addr_t mapping;
        u32 idx, i;
+       __le32 device_addr;
 
        spin_lock_irqsave(&priv->lock, flags);
        idx = le32_to_cpu(ring_control->host_idx[1]);
        i = idx % ARRAY_SIZE(ring_control->tx_data);
+       device_addr = ((struct p54_hdr *)skb->data)->req_id;
 
        mapping = pci_map_single(priv->pdev, skb->data, skb->len,
                                 PCI_DMA_TODEVICE);
@@ -346,7 +348,7 @@ static void p54p_tx(struct ieee80211_hw *dev, struct 
sk_buff *skb)
 
        desc = &ring_control->tx_data[i];
        desc->host_addr = cpu_to_le32(mapping);
-       desc->device_addr = ((struct p54_hdr *)skb->data)->req_id;
+       desc->device_addr = device_addr;
        desc->len = cpu_to_le16(skb->len);
        desc->flags = 0;
 
-- 
2.17.1