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Diffstat (limited to 'Documentation/spi')
| -rw-r--r-- | Documentation/spi/spi-summary | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary index c6152d1ff2b0..761debf748e9 100644 --- a/Documentation/spi/spi-summary +++ b/Documentation/spi/spi-summary @@ -363,6 +363,22 @@ upper boundaries might include sysfs (especially for sensor readings), the input layer, ALSA, networking, MTD, the character device framework, or other Linux subsystems. +Note that there are two types of memory your driver must manage as part +of interacting with SPI devices. + + - I/O buffers use the usual Linux rules, and must be DMA-safe. + You'd normally allocate them from the heap or free page pool. + Don't use the stack, or anything that's declared "static". + + - The spi_message and spi_transfer metadata used to glue those + I/O buffers into a group of protocol transactions. These can + be allocated anywhere it's convenient, including as part of + other allocate-once driver data structures. Zero-init these. + +If you like, spi_message_alloc() and spi_message_free() convenience +routines are available to allocate and zero-initialize an spi_message +with several transfers. + How do I write an "SPI Master Controller Driver"? ------------------------------------------------- |