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spi: expose master transfer size limitation.

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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 <hramrach@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Michal Suchanek 2015-12-02 10:38:21 +00:00 committed by Mark Brown
parent 8005c49d9a
commit 4acad4aae1
1 changed files with 15 additions and 0 deletions
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15
include/linux/spi/spi.h
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@ -425,6 +425,12 @@ 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;
@ -832,6 +838,15 @@ extern int spi_async(struct spi_device *spi, struct spi_message *message);
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