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Message-Id: <1273546529-16846-3-git-send-email-fujita.tomonori@lab.ntt.co.jp>
Date: Tue, 11 May 2010 11:55:29 +0900
From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To: akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org, fujita.tomonori@....ntt.co.jp
Subject: [PATCH -mm 3/3] Documentation: move the error handling to the better place in DMA-API-HOWTO
Handing DMA mapping errors is essential. Let's put it in the more
appropriate place rather than the end of the doc.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
---
Documentation/DMA-API-HOWTO.txt | 60 +++++++++++++++++++-------------------
1 files changed, 30 insertions(+), 30 deletions(-)
diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt
index c3ab456..bfd94e9 100644
--- a/Documentation/DMA-API-HOWTO.txt
+++ b/Documentation/DMA-API-HOWTO.txt
@@ -639,6 +639,36 @@ is planned to completely remove virt_to_bus() and bus_to_virt() as
they are entirely deprecated. Some ports already do not provide these
as it is impossible to correctly support them.
+ Handling Errors
+
+DMA address space is limited on some architectures and an allocation
+failure can be determined by:
+
+- checking if dma_alloc_coherent returns NULL or dma_map_sg returns 0
+
+- checking the returned dma_addr_t of dma_map_single and dma_map_page
+ by using dma_mapping_error():
+
+ dma_addr_t dma_handle;
+
+ dma_handle = dma_map_single(dev, addr, size, direction);
+ if (dma_mapping_error(dev, dma_handle)) {
+ /*
+ * reduce current DMA mapping usage,
+ * delay and try again later or
+ * reset driver.
+ */
+ }
+
+Networking drivers must call dev_kfree_skb to free the socket buffer
+and return NETDEV_TX_OK if the DMA mapping fails on the transmit hook
+(ndo_start_xmit). This means that the socket buffer is just dropped in
+the failure case.
+
+SCSI drivers must return SCSI_MLQUEUE_HOST_BUSY if the DMA mapping
+fails in the queuecommand hook. This means that the SCSI subsystem
+passes the command to the driver again later.
+
Optimizing Unmap State Space Consumption
On many platforms, dma_unmap_{single,page}() is simply a nop.
@@ -710,36 +740,6 @@ to "Closing".
2) More to come...
- Handling Errors
-
-DMA address space is limited on some architectures and an allocation
-failure can be determined by:
-
-- checking if dma_alloc_coherent returns NULL or dma_map_sg returns 0
-
-- checking the returned dma_addr_t of dma_map_single and dma_map_page
- by using dma_mapping_error():
-
- dma_addr_t dma_handle;
-
- dma_handle = dma_map_single(dev, addr, size, direction);
- if (dma_mapping_error(dev, dma_handle)) {
- /*
- * reduce current DMA mapping usage,
- * delay and try again later or
- * reset driver.
- */
- }
-
-Networking drivers must call dev_kfree_skb to free the socket buffer
-and return NETDEV_TX_OK if the DMA mapping fails on the transmit hook
-(ndo_start_xmit). This means that the socket buffer is just dropped in
-the failure case.
-
-SCSI drivers must return SCSI_MLQUEUE_HOST_BUSY if the DMA mapping
-fails in the queuecommand hook. This means that the SCSI subsystem
-passes the command to the driver again later.
-
Closing
This document, and the API itself, would not be in its current
--
1.6.5
--
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