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STRUCT SPI_MESSAGE(9) Serial Peripheral Interface (S STRUCT SPI_MESSAGE(9)

NAME

struct_spi_message - one multi-segment SPI transaction

SYNOPSIS

struct spi_message {
  struct list_head transfers;
  struct spi_device * spi;
  unsigned is_dma_mapped:1;
  void (* complete) (void *context);
  void * context;
  unsigned frame_length;
  unsigned actual_length;
  int status;
  struct list_head queue;
  void * state;
  struct list_head resources;
};

MEMBERS

transfers
list of transfer segments in this transaction
spi
SPI device to which the transaction is queued
is_dma_mapped
if true, the caller provided both dma and cpu virtual addresses for each transfer buffer
complete
called to report transaction completions
context
the argument to complete when it's called
frame_length
the total number of bytes in the message
actual_length
the total number of bytes that were transferred in all successful segments
status
zero for success, else negative errno
queue
for use by whichever driver currently owns the message
state
for use by whichever driver currently owns the message
resources
for resource management when the spi message is processed

DESCRIPTION

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 always 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.

COPYRIGHT

January 2017 Kernel Hackers Manual 4.8.