Applied "spi: expose master transfer size limitation." to the spi tree

Applied "spi: expose master transfer size limitation." to the spi tree

[Mark Brown]

The patch

   spi: expose master transfer size limitation.

has been applied to the spi tree at

   git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From 4acad4aae10d1fa79a075b38b5c73772c44f576c Mon Sep 17 00:00:00 2001
From: Michal Suchanek <hramrach-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
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-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Signed-off-by: Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 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 cce80e6dc7d1..3eebc6c235fb 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
-- 
2.7.0.rc3

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