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r: 198831
b: refs/heads/master
c: 4ae9ca8
h: refs/heads/master
i:
  198829: 889bcd9
  198827: 9edbed0
  198823: c6d5e10
  198815: 89aa64a
v: v3
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FUJITA Tomonori authored and Linus Torvalds committed May 27, 2010
1 parent fa78355 commit 30af8ce
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2 changes: 1 addition & 1 deletion [refs]
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---
refs/heads/master: b02de871617be353c941edce5f7c22bb18499b4e
refs/heads/master: 4ae9ca825e3e28441ef8155c1a81e4c14dfbf38d
60 changes: 30 additions & 30 deletions trunk/Documentation/DMA-API-HOWTO.txt
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Expand Up @@ -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.
Expand Down Expand Up @@ -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
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