diff options
Diffstat (limited to 'Documentation/driver-api/dmaengine')
| -rw-r--r-- | Documentation/driver-api/dmaengine/client.rst | 4 | ||||
| -rw-r--r-- | Documentation/driver-api/dmaengine/provider.rst | 49 |
2 files changed, 52 insertions, 1 deletions
diff --git a/Documentation/driver-api/dmaengine/client.rst b/Documentation/driver-api/dmaengine/client.rst index b0f32cfc38c2..09a3f66dcd26 100644 --- a/Documentation/driver-api/dmaengine/client.rst +++ b/Documentation/driver-api/dmaengine/client.rst @@ -86,7 +86,9 @@ The details of these operations are: - interleaved_dma: This is common to Slave as well as M2M clients. For slave address of devices' fifo could be already known to the driver. Various types of operations could be expressed by setting - appropriate values to the 'dma_interleaved_template' members. + appropriate values to the 'dma_interleaved_template' members. Cyclic + interleaved DMA transfers are also possible if supported by the channel by + setting the DMA_PREP_REPEAT transfer flag. A non-NULL return of this transfer API represents a "descriptor" for the given transaction. diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst index 954422c2b704..ab82c8f21d31 100644 --- a/Documentation/driver-api/dmaengine/provider.rst +++ b/Documentation/driver-api/dmaengine/provider.rst @@ -239,6 +239,27 @@ Currently, the types available are: want to transfer a portion of uncompressed data directly to the display to print it +- DMA_REPEAT + + - The device supports repeated transfers. A repeated transfer, indicated by + the DMA_PREP_REPEAT transfer flag, is similar to a cyclic transfer in that + it gets automatically repeated when it ends, but can additionally be + replaced by the client. + + - This feature is limited to interleaved transfers, this flag should thus not + be set if the DMA_INTERLEAVE flag isn't set. This limitation is based on + the current needs of DMA clients, support for additional transfer types + should be added in the future if and when the need arises. + +- DMA_LOAD_EOT + + - The device supports replacing repeated transfers at end of transfer (EOT) + by queuing a new transfer with the DMA_PREP_LOAD_EOT flag set. + + - Support for replacing a currently running transfer at another point (such + as end of burst instead of end of transfer) will be added in the future + based on DMA clients needs, if and when the need arises. + These various types will also affect how the source and destination addresses change over time. @@ -531,6 +552,34 @@ DMA_CTRL_REUSE writes for which the descriptor should be in different format from normal data descriptors. +- DMA_PREP_REPEAT + + - If set, the transfer will be automatically repeated when it ends until a + new transfer is queued on the same channel with the DMA_PREP_LOAD_EOT flag. + If the next transfer to be queued on the channel does not have the + DMA_PREP_LOAD_EOT flag set, the current transfer will be repeated until the + client terminates all transfers. + + - This flag is only supported if the channel reports the DMA_REPEAT + capability. + +- DMA_PREP_LOAD_EOT + + - If set, the transfer will replace the transfer currently being executed at + the end of the transfer. + + - This is the default behaviour for non-repeated transfers, specifying + DMA_PREP_LOAD_EOT for non-repeated transfers will thus make no difference. + + - When using repeated transfers, DMA clients will usually need to set the + DMA_PREP_LOAD_EOT flag on all transfers, otherwise the channel will keep + repeating the last repeated transfer and ignore the new transfers being + queued. Failure to set DMA_PREP_LOAD_EOT will appear as if the channel was + stuck on the previous transfer. + + - This flag is only supported if the channel reports the DMA_LOAD_EOT + capability. + General Design Notes ==================== |