From 4acad4aae10d1fa79a075b38b5c73772c44f576c Mon Sep 17 00:00:00 2001 From: Michal Suchanek Date: Wed, 2 Dec 2015 10:38:21 +0000 Subject: [PATCH] spi: expose master transfer size limitation. On some SPI controllers it is not feasible to transfer arbitrary amount of data at once. When the limit on transfer size is a few kilobytes at least it makes sense to use the SPI hardware rather than reverting to gpio driver. The protocol drivers need a way to check that they do not sent overly long messages, though. Signed-off-by: Michal Suchanek Signed-off-by: Mark Brown --- include/linux/spi/spi.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) --- a/include/linux/spi/spi.h +++ b/include/linux/spi/spi.h @@ -428,6 +428,12 @@ struct spi_master { #define SPI_MASTER_MUST_RX BIT(3) /* requires rx */ #define SPI_MASTER_MUST_TX BIT(4) /* requires tx */ + /* + * on some hardware transfer size may be constrained + * the limit may depend on device transfer settings + */ + size_t (*max_transfer_size)(struct spi_device *spi); + /* lock and mutex for SPI bus locking */ spinlock_t bus_lock_spinlock; struct mutex bus_lock_mutex; @@ -837,6 +843,15 @@ extern int spi_async(struct spi_device * extern int spi_async_locked(struct spi_device *spi, struct spi_message *message); +static inline size_t +spi_max_transfer_size(struct spi_device *spi) +{ + struct spi_master *master = spi->master; + if (!master->max_transfer_size) + return SIZE_MAX; + return master->max_transfer_size(spi); +} + /*---------------------------------------------------------------------------*/ /* All these synchronous SPI transfer routines are utilities layered