If the driver is unloaded while there is still a host command in
flight, its tfd will be freed by iwl_tx_queue_free.
This function is called for both types of queues: Tx queues and cmd
queue. This didn't take in count the fact that in Tx queues, tfds are
mapped as TO_DEVICE (besides the first TB), whereas in cmd queue, all
TBs are mapped as BIDI.

Hence, tx_queue_free unmapped the second (and higher) TB of each tfd
in the cmd queue as TO_DEVICE, whereas they must be freed as BIDI.
This means that if a multi TFD is in flight while we unload the
driver (which is quite unlikely but can happen), we will get the
warning below.

This patch fixes this.

[  445.234060] ------------[ cut here ]------------
[  445.236273] WARNING: at lib/dma-debug.c:861 check_unmap+0x337/0x780()
[  445.236654] iwlagn 0000:02:00.0: DMA-API: device driver frees DMA memory with different direction [device address=0x0000000126950540] [size=8 bytes] [mapped with DMA_BIDIRECTIONAL] [unmapped with DMA_TO_DEVICE]
[  445.236654] Modules linked in: ...
[  445.236654] Pid: 1415, comm: modprobe Not tainted 3.1.0-rc4-wl-65912-g5215ff1-dirty #79
[  445.236654] Call Trace:
[  445.236654]  [<ffffffff81043a51>] warn_slowpath_common+0x71/0xa0
[  445.236654]  [<ffffffff81043b37>] warn_slowpath_fmt+0x47/0x50
[  445.236654]  [<ffffffff8121e687>] check_unmap+0x337/0x780
[  445.236654]  [<ffffffff810e9136>] ? free_one_page+0x156/0x320
[  445.236654]  [<ffffffff8121ec5a>] debug_dma_unmap_page+0x5a/0x60
[  445.236654]  [<ffffffffa021d701>] iwlagn_unmap_tfd.isra.11+0x121/0x1c0 [iwlagn]
[  445.236654]  [<ffffffffa021ddf2>] iwlagn_txq_free_tfd+0x42/0x70 [iwlagn]
[  445.236654]  [<ffffffffa02121de>] iwl_tx_queue_unmap+0x4e/0x70 [iwlagn]
[  445.236654]  [<ffffffffa0212fad>] iwl_trans_pcie_tx_free+0x10d/0x440 [iwlagn]
[  445.236654]  [<ffffffff81064959>] ? destroy_workqueue+0xb9/0x1e0
[  445.236654]  [<ffffffffa021330a>] iwl_trans_pcie_free+0x2a/0x2c0 [iwlagn]
[  445.236654]  [<ffffffffa022f4f2>] iwl_remove+0x149/0x17e [iwlagn]
[  445.236654]  [<ffffffffa022f546>] iwl_pci_remove+0x1f/0x65 [iwlagn]
[  445.236654]  [<ffffffff81228337>] pci_device_remove+0x47/0x120
[  445.236654]  [<ffffffff8134566c>] __device_release_driver+0x7c/0xe0
[  445.236654]  [<ffffffff81345dc8>] driver_detach+0xc8/0xd0
[  445.236654]  [<ffffffff813454c8>] bus_remove_driver+0x88/0xe0
[  445.236654]  [<ffffffff81346572>] driver_unregister+0x62/0xa0
[  445.236654]  [<ffffffff812271d4>] pci_unregister_driver+0x44/0xc0
[  445.236654]  [<ffffffffa0211ce5>] iwl_pci_unregister_driver+0x15/0x20 [iwlagn]
[  445.236654]  [<ffffffffa022f595>] iwl_exit+0x9/0xa74 [iwlagn]
[  445.236654]  [<ffffffff810918f4>] sys_delete_module+0x184/0x240
[  445.236654]  [<ffffffff81452ece>] ? retint_swapgs+0xe/0x13
[  445.236654]  [<ffffffff8121098e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[  445.236654]  [<ffffffff81459e2b>] system_call_fastpath+0x16/0x1b
[  445.236654] ---[ end trace 1fbc362b7dbe5d74 ]---
[  445.236654] Mapped at:
[  445.236654]  [<ffffffff8121d7cb>] debug_dma_map_page+0x8b/0x150
[  445.236654]  [<ffffffffa021e7b7>] iwl_enqueue_hcmd+0x837/0xa40 [iwlagn]
[  445.236654]  [<ffffffffa021f92d>] iwl_trans_pcie_send_cmd+0x8d/0x580 [iwlagn]
[  445.236654]  [<ffffffffa01f7c75>] iwl_send_calib_results+0x75/0xd0 [iwlagn]
[  445.236654]  [<ffffffffa01f21f6>] iwlagn_alive_notify+0x196/0x1f0 [iwlagn]
[  445.386500] iwlagn 0000:02:00.0: PCI INT A disabled

Reported-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>