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diff --git a/Documentation/crypto/async-tx-api.txt b/Documentation/crypto/async-tx-api.txt deleted file mode 100644 index 7bf1be20d93a..000000000000 --- a/Documentation/crypto/async-tx-api.txt +++ /dev/null @@ -1,225 +0,0 @@ - Asynchronous Transfers/Transforms API - -1 INTRODUCTION - -2 GENEALOGY - -3 USAGE -3.1 General format of the API -3.2 Supported operations -3.3 Descriptor management -3.4 When does the operation execute? -3.5 When does the operation complete? -3.6 Constraints -3.7 Example - -4 DMAENGINE DRIVER DEVELOPER NOTES -4.1 Conformance points -4.2 "My application needs exclusive control of hardware channels" - -5 SOURCE - ---- - -1 INTRODUCTION - -The async_tx API provides methods for describing a chain of asynchronous -bulk memory transfers/transforms with support for inter-transactional -dependencies. It is implemented as a dmaengine client that smooths over -the details of different hardware offload engine implementations. Code -that is written to the API can optimize for asynchronous operation and -the API will fit the chain of operations to the available offload -resources. - -2 GENEALOGY - -The API was initially designed to offload the memory copy and -xor-parity-calculations of the md-raid5 driver using the offload engines -present in the Intel(R) Xscale series of I/O processors. It also built -on the 'dmaengine' layer developed for offloading memory copies in the -network stack using Intel(R) I/OAT engines. The following design -features surfaced as a result: -1/ implicit synchronous path: users of the API do not need to know if - the platform they are running on has offload capabilities. The - operation will be offloaded when an engine is available and carried out - in software otherwise. -2/ cross channel dependency chains: the API allows a chain of dependent - operations to be submitted, like xor->copy->xor in the raid5 case. The - API automatically handles cases where the transition from one operation - to another implies a hardware channel switch. -3/ dmaengine extensions to support multiple clients and operation types - beyond 'memcpy' - -3 USAGE - -3.1 General format of the API: -struct dma_async_tx_descriptor * -async_<operation>(<op specific parameters>, struct async_submit ctl *submit) - -3.2 Supported operations: -memcpy - memory copy between a source and a destination buffer -memset - fill a destination buffer with a byte value -xor - xor a series of source buffers and write the result to a - destination buffer -xor_val - xor a series of source buffers and set a flag if the - result is zero. The implementation attempts to prevent - writes to memory -pq - generate the p+q (raid6 syndrome) from a series of source buffers -pq_val - validate that a p and or q buffer are in sync with a given series of - sources -datap - (raid6_datap_recov) recover a raid6 data block and the p block - from the given sources -2data - (raid6_2data_recov) recover 2 raid6 data blocks from the given - sources - -3.3 Descriptor management: -The return value is non-NULL and points to a 'descriptor' when the operation -has been queued to execute asynchronously. Descriptors are recycled -resources, under control of the offload engine driver, to be reused as -operations complete. When an application needs to submit a chain of -operations it must guarantee that the descriptor is not automatically recycled -before the dependency is submitted. This requires that all descriptors be -acknowledged by the application before the offload engine driver is allowed to -recycle (or free) the descriptor. A descriptor can be acked by one of the -following methods: -1/ setting the ASYNC_TX_ACK flag if no child operations are to be submitted -2/ submitting an unacknowledged descriptor as a dependency to another - async_tx call will implicitly set the acknowledged state. -3/ calling async_tx_ack() on the descriptor. - -3.4 When does the operation execute? -Operations do not immediately issue after return from the -async_<operation> call. Offload engine drivers batch operations to -improve performance by reducing the number of mmio cycles needed to -manage the channel. Once a driver-specific threshold is met the driver -automatically issues pending operations. An application can force this -event by calling async_tx_issue_pending_all(). This operates on all -channels since the application has no knowledge of channel to operation -mapping. - -3.5 When does the operation complete? -There are two methods for an application to learn about the completion -of an operation. -1/ Call dma_wait_for_async_tx(). This call causes the CPU to spin while - it polls for the completion of the operation. It handles dependency - chains and issuing pending operations. -2/ Specify a completion callback. The callback routine runs in tasklet - context if the offload engine driver supports interrupts, or it is - called in application context if the operation is carried out - synchronously in software. The callback can be set in the call to - async_<operation>, or when the application needs to submit a chain of - unknown length it can use the async_trigger_callback() routine to set a - completion interrupt/callback at the end of the chain. - -3.6 Constraints: -1/ Calls to async_<operation> are not permitted in IRQ context. Other - contexts are permitted provided constraint #2 is not violated. -2/ Completion callback routines cannot submit new operations. This - results in recursion in the synchronous case and spin_locks being - acquired twice in the asynchronous case. - -3.7 Example: -Perform a xor->copy->xor operation where each operation depends on the -result from the previous operation: - -void callback(void *param) -{ - struct completion *cmp = param; - - complete(cmp); -} - -void run_xor_copy_xor(struct page **xor_srcs, - int xor_src_cnt, - struct page *xor_dest, - size_t xor_len, - struct page *copy_src, - struct page *copy_dest, - size_t copy_len) -{ - struct dma_async_tx_descriptor *tx; - addr_conv_t addr_conv[xor_src_cnt]; - struct async_submit_ctl submit; - addr_conv_t addr_conv[NDISKS]; - struct completion cmp; - - init_async_submit(&submit, ASYNC_TX_XOR_DROP_DST, NULL, NULL, NULL, - addr_conv); - tx = async_xor(xor_dest, xor_srcs, 0, xor_src_cnt, xor_len, &submit) - - submit->depend_tx = tx; - tx = async_memcpy(copy_dest, copy_src, 0, 0, copy_len, &submit); - - init_completion(&cmp); - init_async_submit(&submit, ASYNC_TX_XOR_DROP_DST | ASYNC_TX_ACK, tx, - callback, &cmp, addr_conv); - tx = async_xor(xor_dest, xor_srcs, 0, xor_src_cnt, xor_len, &submit); - - async_tx_issue_pending_all(); - - wait_for_completion(&cmp); -} - -See include/linux/async_tx.h for more information on the flags. See the -ops_run_* and ops_complete_* routines in drivers/md/raid5.c for more -implementation examples. - -4 DRIVER DEVELOPMENT NOTES - -4.1 Conformance points: -There are a few conformance points required in dmaengine drivers to -accommodate assumptions made by applications using the async_tx API: -1/ Completion callbacks are expected to happen in tasklet context -2/ dma_async_tx_descriptor fields are never manipulated in IRQ context -3/ Use async_tx_run_dependencies() in the descriptor clean up path to - handle submission of dependent operations - -4.2 "My application needs exclusive control of hardware channels" -Primarily this requirement arises from cases where a DMA engine driver -is being used to support device-to-memory operations. A channel that is -performing these operations cannot, for many platform specific reasons, -be shared. For these cases the dma_request_channel() interface is -provided. - -The interface is: -struct dma_chan *dma_request_channel(dma_cap_mask_t mask, - dma_filter_fn filter_fn, - void *filter_param); - -Where dma_filter_fn is defined as: -typedef bool (*dma_filter_fn)(struct dma_chan *chan, void *filter_param); - -When the optional 'filter_fn' parameter is set to NULL -dma_request_channel simply returns the first channel that satisfies the -capability mask. Otherwise, when the mask parameter is insufficient for -specifying the necessary channel, the filter_fn routine can be used to -disposition the available channels in the system. The filter_fn routine -is called once for each free channel in the system. Upon seeing a -suitable channel filter_fn returns DMA_ACK which flags that channel to -be the return value from dma_request_channel. A channel allocated via -this interface is exclusive to the caller, until dma_release_channel() -is called. - -The DMA_PRIVATE capability flag is used to tag dma devices that should -not be used by the general-purpose allocator. It can be set at -initialization time if it is known that a channel will always be -private. Alternatively, it is set when dma_request_channel() finds an -unused "public" channel. - -A couple caveats to note when implementing a driver and consumer: -1/ Once a channel has been privately allocated it will no longer be - considered by the general-purpose allocator even after a call to - dma_release_channel(). -2/ Since capabilities are specified at the device level a dma_device - with multiple channels will either have all channels public, or all - channels private. - -5 SOURCE - -include/linux/dmaengine.h: core header file for DMA drivers and api users -drivers/dma/dmaengine.c: offload engine channel management routines -drivers/dma/: location for offload engine drivers -include/linux/async_tx.h: core header file for the async_tx api -crypto/async_tx/async_tx.c: async_tx interface to dmaengine and common code -crypto/async_tx/async_memcpy.c: copy offload -crypto/async_tx/async_xor.c: xor and xor zero sum offload |