RE: [PATCH]iwlan dma mapping read and write changes

From: Winkler, Tomas
Date: Wed Feb 11 2009 - 16:30:20 EST




>-----Original Message-----
>From: Yu, Fenghua
>Sent: Wednesday, February 11, 2009 8:27 PM
>To: David Woodhouse; Ingo Molnar; Stephen Rothwell; Andrew Morton; Johannes
>Berg; Grumbach, Emmanuel; Winkler, Tomas; Zhu, Yi; Chris Wright
>Cc: LKML; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
>Subject: [PATCH]iwlan dma mapping read and write changes
>
>When iwlan runs on IOMMU, IOMMU generates a lot of PTE write faults because
>PTE
>write bit is not set on some of PTE's. This is because iwlan driver calls
>DMA
>mapping with PCI_DMA_TODEVICE which is read only in mapping PTE. But iwlan
>device
>actually writes to the mapped page to update its contents. This issue is
>not
>exposed in swiotlb. But VT-d hardware can capture this fault and stop the
>fault
>transaction.
>
>The following patch fixes the issue.
>
>Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Acked-by: Tomas Winkler <tomas.winkler@xxxxxxxxx>

Indeed the firmware/ucode write back to host memory to update retry counter for APMDU packets. I'm not sure if this is needed for legacy traffic, though.

>---
>
> iwl-tx.c | 8 ++++----
> 1 files changed, 4 insertions(+), 4 deletions(-)
>
>--- a/drivers/net/wireless/iwlwifi/iwl-tx.c.orig 2009-02-10
>21:28:45.000000000 -0800
>+++ b/drivers/net/wireless/iwlwifi/iwl-tx.c 2009-02-10
>21:41:02.000000000 -0800
>@@ -148,7 +148,7 @@ static void iwl_hw_txq_free_tfd(struct i
> pci_unmap_single(dev,
> pci_unmap_addr(&txq->cmd[index]->meta, mapping),
> pci_unmap_len(&txq->cmd[index]->meta, len),
>- PCI_DMA_TODEVICE);
>+ PCI_DMA_BIDIRECTIONAL);
>
> /* Unmap chunks, if any. */
> for (i = 1; i < num_tbs; i++) {
>@@ -964,7 +964,7 @@ int iwl_tx_skb(struct iwl_priv *priv, st
> * within command buffer array. */
> txcmd_phys = pci_map_single(priv->pci_dev,
> out_cmd, sizeof(struct iwl_cmd),
>- PCI_DMA_TODEVICE);
>+ PCI_DMA_BIDIRECTIONAL);
> pci_unmap_addr_set(&out_cmd->meta, mapping, txcmd_phys);
> pci_unmap_len_set(&out_cmd->meta, len, sizeof(struct iwl_cmd));
> /* Add buffer containing Tx command and MAC(!) header to TFD's
>@@ -1115,7 +1115,7 @@ int iwl_enqueue_hcmd(struct iwl_priv *pr
> IWL_MAX_SCAN_SIZE : sizeof(struct iwl_cmd);
>
> phys_addr = pci_map_single(priv->pci_dev, out_cmd,
>- len, PCI_DMA_TODEVICE);
>+ len, PCI_DMA_BIDIRECTIONAL);
> pci_unmap_addr_set(&out_cmd->meta, mapping, phys_addr);
> pci_unmap_len_set(&out_cmd->meta, len, len);
> phys_addr += offsetof(struct iwl_cmd, hdr);
>@@ -1212,7 +1212,7 @@ static void iwl_hcmd_queue_reclaim(struc
> pci_unmap_single(priv->pci_dev,
> pci_unmap_addr(&txq->cmd[cmd_idx]->meta, mapping),
> pci_unmap_len(&txq->cmd[cmd_idx]->meta, len),
>- PCI_DMA_TODEVICE);
>+ PCI_DMA_BIDIRECTIONAL);
>
> for (idx = iwl_queue_inc_wrap(idx, q->n_bd); q->read_ptr != idx;
> q->read_ptr = iwl_queue_inc_wrap(q->read_ptr, q->n_bd)) {
---------------------------------------------------------------------
Intel Israel (74) Limited

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