Lines Matching refs:to
10 They have a given number of channels to use for the DMA transfers, and
14 to serve several to any requests. To simplify, channels are the
18 The request lines actually correspond to physical lines going from the
19 DMA-eligible devices to the controller itself. Whenever the device
20 will want to start a transfer, it will assert a DMA request (DRQ) by
25 byte of data from one buffer to another, until the transfer size has
29 require a specific number of bits to be transferred in a single
30 cycle. For example, we may want to transfer as much data as the
31 physical bus allows to maximize performances when doing a simple
33 that requires data to be written exactly 16 or 24 bits at a time. This
42 reads/writes it's allowed to do without the controller splitting the
45 Our theoretical DMA controller would then only be able to do transfers
47 transfers we usually have are not, and want to copy data from
48 non-contiguous buffers to a contiguous buffer, which is called
53 quite simple DMA controller that doesn't support it, and we'll have to
57 The latter are usually programmed using a collection of chunks to
63 or the first item of the list to one channel of the DMA controller,
65 to know where to fetch the data from.
75 default, and you have to enable this in your slave device driver first
76 whenever you're willing to use DMA.
78 These were just the general memory-to-memory (also called mem2mem) or
79 memory-to-device (mem2dev) kind of transfers. Most devices often
87 async TX API, to offload operations such as memory copy, XOR,
88 cryptography, etc., basically any memory to memory operation.
90 Over time, the need for memory to device transfers arose, and
93 accommodates that API in some cases, and made some design choices to
109 The first thing you need to do in your driver is to allocate this
111 need to initialize a few fields in there:
128 - Granularity of the transfer residue reported to dma_set_residue.
135 -> Your device is able to report which chunks have been
138 -> Your device is able to report which burst have been
141 * dev: should hold the pointer to the struct device associated
142 to your current driver instance.
147 The next thing you need is to set which transaction types your device
151 various types of transaction supported, and you need to modify this
160 - The device is able to do memory to memory copies
163 - The device is able to perform XOR operations on memory areas
164 - Used to accelerate XOR intensive tasks, such as RAID5
167 - The device is able to perform parity check using the XOR
171 - The device is able to perform RAID6 P+Q computations, P being a
175 - The device is able to perform parity check using RAID6 P+Q
179 - The device is able to trigger a dummy transfer that will
181 - Used by the client drivers to register a callback that will be
185 - The device supports memory to memory scatter-gather
188 scatter-gather transfer, with a single chunk to transfer, it's a
201 - The device can handle device to memory transfers, including
203 - While in the mem2mem case we were having two distinct types to
204 deal with a single chunk to copy or a collection of them, here,
205 we just have a single transaction type that is supposed to
207 - If you want to transfer a single contiguous memory buffer,
213 loop over itself, with the last item pointing to the first.
214 - It's usually used for audio transfers, where you want to operate
220 to a non-contiguous buffer, opposed to DMA_SLAVE that can
221 transfer data from a non-contiguous data set to a continuous
224 want to transfer a portion of uncompressed data directly to the
225 display to print it
230 Addresses pointing to RAM are typically incremented (or decremented)
232 (DMA_CYCLIC). Addresses pointing to a device's register (e.g. a FIFO)
239 order to implement the actual logic, now that we described what
240 operations we were able to perform.
242 The functions that we have to fill in there, and hence have to
250 time on the channel associated to that driver.
252 resources in order for that channel to be useful for your
264 flag, in order not to potentially sleep, but without depleting
266 - Drivers should try to pre-allocate any memory they might need
267 during the transfer setup at probe time to avoid putting to
276 - You'll also need to set two fields in this structure:
281 + tx_submit: A pointer to a function you have to implement,
282 that is supposed to push the current
283 transaction descriptor to a pending queue, waiting
284 for issue_pending to be called.
289 should move to the next transaction in the list.
293 - Should report the bytes left to go over on the given channel
297 - Should use dma_set_residue to report it
309 configuration to use.
311 field is deprecated in favor of the direction argument given to
314 set or expected to be set for memcpy operations.
334 where to put them)
349 client acknowledges receipt, i.e. has has a chance to establish any
361 - As a consequence, if a device driver wants to skip the dma_map_sg() and
377 most work to a tasklet, including the start of a new transfer whenever
386 transfer in your tasklet, move that part to the interrupt handler in
387 order to have a shorter idle window (that we can't really avoid
394 that can be queued to buffers before being flushed to