fbdev: fix frame buffer devices menu

[safe/jmp/linux-2.6] / Documentation / DMA-API-HOWTO.txt

diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt
index c3ab456..98ce517 100644 (file)
--- 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.
@@ -708,37 +738,20 @@ to "Closing".
    CONFIG_NEED_SG_DMA_LENGTH if the architecture supports IOMMUs
    (including software IOMMU).
 
-2) More to come...
-
-                       Handling Errors
-
-DMA address space is limited on some architectures and an allocation
-failure can be determined by:
+2) ARCH_KMALLOC_MINALIGN
 
-- checking if dma_alloc_coherent returns NULL or dma_map_sg returns 0
+   Architectures must ensure that kmalloc'ed buffer is
+   DMA-safe. Drivers and subsystems depend on it. If an architecture
+   isn't fully DMA-coherent (i.e. hardware doesn't ensure that data in
+   the CPU cache is identical to data in main memory),
+   ARCH_KMALLOC_MINALIGN must be set so that the memory allocator
+   makes sure that kmalloc'ed buffer doesn't share a cache line with
+   the others. See arch/arm/include/asm/cache.h as an example.
 
-- 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.
+   Note that ARCH_KMALLOC_MINALIGN is about DMA memory alignment
+   constraints. You don't need to worry about the architecture data
+   alignment constraints (e.g. the alignment constraints about 64-bit
+   objects).
 
                           Closing