struct spi_message — one multi-segment SPI transaction
struct spi_message {
struct list_head transfers;
struct spi_device * spi;
unsigned is_dma_mapped:1;
void (* complete) (void *context);
void * context;
unsigned actual_length;
int status;
struct list_head queue;
void * state;
}; list of transfer segments in this transaction
SPI device to which the transaction is queued
if true, the caller provided both dma and cpu virtual addresses for each transfer buffer
called to report transaction completions
the argument to complete when it's called
the total number of bytes that were transferred in all successful segments
zero for success, else negative errno
for use by whichever driver currently owns the message
for use by whichever driver currently owns the message
A spi_message is used to execute an atomic sequence of data transfers,
each represented by a struct spi_transfer. The sequence is “atomic”
in the sense that no other spi_message may use that SPI bus until that
sequence completes. On some systems, many such sequences can execute as
as single programmed DMA transfer. On all systems, these messages are
queued, and might complete after transactions to other devices. Messages
sent to a given spi_device are alway executed in FIFO order.
The code that submits an spi_message (and its spi_transfers) to the lower layers is responsible for managing its memory. Zero-initialize every field you don't set up explicitly, to insulate against future API updates. After you submit a message and its transfers, ignore them until its completion callback.