target/linux/brcm63xx/patches-4.4/000-4.5-20-spi-expose-master-transfer-size-limitation.patch

   1 From 4acad4aae10d1fa79a075b38b5c73772c44f576c Mon Sep 17 00:00:00 2001
   2 From: Michal Suchanek <hramrach@gmail.com>
   3 Date: Wed, 2 Dec 2015 10:38:21 +0000
   4 Subject: [PATCH] spi: expose master transfer size limitation.
   5
   6 On some SPI controllers it is not feasible to transfer arbitrary amount
   7 of data at once.
   8
   9 When the limit on transfer size is a few kilobytes at least it makes
  10 sense to use the SPI hardware rather than reverting to gpio driver.
  11
  12 The protocol drivers need a way to check that they do not sent overly
  13 long messages, though.
  14
  15 Signed-off-by: Michal Suchanek <hramrach@gmail.com>
  16 Signed-off-by: Mark Brown <broonie@kernel.org>
  17 ---
  18  include/linux/spi/spi.h | 15 +++++++++++++++
  19  1 file changed, 15 insertions(+)
  20
  21 --- a/include/linux/spi/spi.h
  22 +++ b/include/linux/spi/spi.h
  23 @@ -428,6 +428,12 @@ struct spi_master {
  24  #define SPI_MASTER_MUST_RX      BIT(3)         /* requires rx */
  25  #define SPI_MASTER_MUST_TX      BIT(4)         /* requires tx */
  26
  27 +       /*
  28 +        * on some hardware transfer size may be constrained
  29 +        * the limit may depend on device transfer settings
  30 +        */
  31 +       size_t (*max_transfer_size)(struct spi_device *spi);
  32 +
  33         /* lock and mutex for SPI bus locking */
  34         spinlock_t              bus_lock_spinlock;
  35         struct mutex            bus_lock_mutex;
  36 @@ -837,6 +843,15 @@ extern int spi_async(struct spi_device *
  37  extern int spi_async_locked(struct spi_device *spi,
  38                             struct spi_message *message);
  39
  40 +static inline size_t
  41 +spi_max_transfer_size(struct spi_device *spi)
  42 +{
  43 +       struct spi_master *master = spi->master;
  44 +       if (!master->max_transfer_size)
  45 +               return SIZE_MAX;
  46 +       return master->max_transfer_size(spi);
  47 +}
  48 +
  49  /*---------------------------------------------------------------------------*/
  50
  51  /* All these synchronous SPI transfer routines are utilities layered