[PATCH v6 08/10] spi: expose master transfer size limitation.

[Michal Suchanek]

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 at gmail.com>

---

 - return SIZE_MAX when no limit is known
---
 include/linux/spi/spi.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index cce80e6..3eebc6c 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -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
-- 
2.6.2