iwlwifi: pcie: avoid dma unmap/remap in crash dump

DMA-API debug code pointed out that in this code path we
never check the return value of dma_map_page(), which could
fail.

However, we don't really even want to unmap/remap, we just
want to ensure that we can actually access the last version
of the data that the (now-dead) device may have written, so
only need to dma_sync_single_for_cpu() instead.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210819183728.5987f35883a2.I2d9ea5ecc69a5e5947b546fb15f33363a0595651@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/pcie/trans.c

@@ -2968,8 +2968,8 @@ static u32 iwl_trans_pcie_dump_rbs(struct iwl_trans *trans,
 		struct iwl_rx_mem_buffer *rxb = rxq->queue[i];
 		struct iwl_fw_error_dump_rb *rb;
 
-		dma_unmap_page(trans->dev, rxb->page_dma, max_len,
-			       DMA_FROM_DEVICE);
+		dma_sync_single_for_cpu(trans->dev, rxb->page_dma,
+					max_len, DMA_FROM_DEVICE);
 
 		rb_len += sizeof(**data) + sizeof(*rb) + max_len;
 
@@ -2978,10 +2978,6 @@ static u32 iwl_trans_pcie_dump_rbs(struct iwl_trans *trans,
 		rb = (void *)(*data)->data;
 		rb->index = cpu_to_le32(i);
 		memcpy(rb->data, page_address(rxb->page), max_len);
-		/* remap the page for the free benefit */
-		rxb->page_dma = dma_map_page(trans->dev, rxb->page,
-					     rxb->offset, max_len,
-					     DMA_FROM_DEVICE);
 
 		*data = iwl_fw_error_next_data(*data);
 	}