[PATCH] spi: Add spi-bits-per-word binding.

[Adrian Fiergolski <adrian.fiergolski@cern.ch>]

If an SPI controller doesn't support 8 bit transfers
(master->bits_per_word_mask), it will be never registered (tested with
spidev):
of_register_spi_device calls spi_add_device which calls spi_setup. The last
takes as an argument spi_device struct, which, in case of spidev, has
bits_per_word set to 0. Thus, the spi_setup function will set it to default
8. Further, the same function will call __spi_validate_bits_per_word which
will fail the whole registration for controllers not supporting 8 bit
transfers (i.e. xilinx-spi).

Signed-off-by: Adrian Fiergolski <adrian.fiergolski@cern.ch>
---
 Documentation/devicetree/bindings/spi/spi-bus.txt | 40 ++++++++++++-----------
 drivers/spi/spi.c                                 | 18 ++++++++++
 2 files changed, 39 insertions(+), 19 deletions(-)

diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
index 4b1d6e7..8401741 100644
--- a/Documentation/devicetree/bindings/spi/spi-bus.txt
+++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
@@ -43,26 +43,28 @@ cs3 : &gpio1 2 0
 
 SPI slave nodes must be children of the SPI master node and can
 contain the following properties.
-- reg             - (required) chip select address of device.
-- compatible      - (required) name of SPI device following generic names
-		recommended practice.
+- reg               - (required) chip select address of device.
+- compatible        - (required) name of SPI device following generic names
+		      recommended practice.
 - spi-max-frequency - (required) Maximum SPI clocking speed of device in Hz.
-- spi-cpol        - (optional) Empty property indicating device requires
-		inverse clock polarity (CPOL) mode.
-- spi-cpha        - (optional) Empty property indicating device requires
-		shifted clock phase (CPHA) mode.
-- spi-cs-high     - (optional) Empty property indicating device requires
-		chip select active high.
-- spi-3wire       - (optional) Empty property indicating device requires
-		3-wire mode.
-- spi-lsb-first   - (optional) Empty property indicating device requires
-		LSB first mode.
-- spi-tx-bus-width - (optional) The bus width (number of data wires) that is
-                      used for MOSI. Defaults to 1 if not present.
-- spi-rx-bus-width - (optional) The bus width (number of data wires) that is
-                      used for MISO. Defaults to 1 if not present.
-- spi-rx-delay-us  - (optional) Microsecond delay after a read transfer.
-- spi-tx-delay-us  - (optional) Microsecond delay after a write transfer.
+- spi-cpol          - (optional) Empty property indicating device requires
+		      inverse clock polarity (CPOL) mode.
+- spi-cpha          - (optional) Empty property indicating device requires
+		      shifted clock phase (CPHA) mode.
+- spi-cs-high       - (optional) Empty property indicating device requires
+		      chip select active high.
+- spi-3wire         - (optional) Empty property indicating device requires
+		      3-wire mode.
+- spi-lsb-first     - (optional) Empty property indicating device requires
+		      LSB first mode.
+- spi-tx-bus-width  - (optional) The bus width (number of data wires) that is
+                       used for MOSI. Defaults to 1 if not present.
+- spi-rx-bus-width  - (optional) The bus width (number of data wires) that is
+                       used for MISO. Defaults to 1 if not present.
+- spi-rx-delay-us   - (optional) Microsecond delay after a read transfer.
+- spi-tx-delay-us   - (optional) Microsecond delay after a write transfer.
+- spi-bits-per-word - (optional) Word size for a data transfer. Defaults is 8
+                      if not present.
 
 Some SPI controllers and devices support Dual and Quad SPI transfer mode.
 It allows data in the SPI system to be transferred using 2 wires (DUAL) or 4
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 656dd3e..57fe058 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1594,6 +1594,17 @@ of_register_spi_device(struct spi_master *master, struct device_node *nc)
 	}
 	spi->max_speed_hz = value;
 
+	/* Device bits-per-word */
+	if (!of_property_read_u32(nc, "spi-bits-per-word", &value)) {
+		if (value > 32)
+			dev_warn(&master->dev,
+				 "bits-per-word %d not supported\n",
+				 value);
+		else
+			spi->bits_per_word = value;
+	}
+
+
 	/* Store a pointer to the node in the device structure */
 	of_node_get(nc);
 	spi->dev.of_node = nc;
@@ -1673,6 +1684,13 @@ static int acpi_spi_add_resource(struct acpi_resource *ares, void *data)
 
 			spi->max_speed_hz = sb->connection_speed;
 
+			if (sb->data_bit_length > 32)
+				dev_warn(&master->dev,
+					 "bits-per-word %d not supported\n",
+					 sb->data_bit_length);
+			else
+				spi->bits_per_word = sb->data_bit_length;
+
 			if (sb->clock_phase == ACPI_SPI_SECOND_PHASE)
 				spi->mode |= SPI_CPHA;
 			if (sb->clock_polarity == ACPI_SPI_START_HIGH)
-- 
2.9.3