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From 4acad4aae10d1fa79a075b38b5c73772c44f576c Mon Sep 17 00:00:00 2001
From: Michal Suchanek <hramrach@gmail.com>
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 <hramrach@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
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
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