spi: orion: Add direct access mode

This patch adds support for the direct access mode to the Orion SPI
driver which is used on the Marvell Armada based SoCs. In this direct
mode, all data written to (or read from) a specifically mapped MBus
window (linked to one SPI chip-select on one of the SPI controllers)
will be transferred directly to the SPI bus. Without the need to control
the SPI registers in between. This can improve the SPI transfer rate in
such cases.

Both, direct-read and -write mode are supported. But only the write
mode has been tested. This mode especially benefits from the SPI direct
mode, as the data bytes are written head-to-head to the SPI bus,
without any additional addresses.

One use-case for this direct write mode is, programming a FPGA bitstream
image into the FPGA connected to the SPI bus at maximum speed.

This mode is described in chapter "22.5.2 Direct Write to SPI" in the
Marvell Armada XP Functional Spec Datasheet.

Signed-off-by: Stefan Roese <sr@denx.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 48 insertions, 1 deletions

diff --git a/Documentation/devicetree/bindings/spi/spi-orion.txt b/Documentation/devicetree/bindings/spi/spi-orion.txt
index 98bc698..4f629cc 100644
--- a/Documentation/devicetree/bindings/spi/spi-orion.txt
+++ b/Documentation/devicetree/bindings/spi/spi-orion.txt
@@ -8,7 +8,15 @@ Required properties:
     - "marvell,armada-380-spi", for the Armada 38x SoCs
     - "marvell,armada-390-spi", for the Armada 39x SoCs
     - "marvell,armada-xp-spi", for the Armada XP SoCs
-- reg : offset and length of the register set for the device
+- reg : offset and length of the register set for the device.
+	This property can optionally have additional entries to configure
+	the SPI direct access mode that some of the Marvell SoCs support
+	additionally to the normal indirect access (PIO) mode. The values
+	for the MBus "target" and "attribute" are defined in the Marvell
+	SoC "Functional Specifications" Manual in the chapter "Marvell
+	Core Processor Address Decoding".
+	The eight register sets following the control registers refer to
+	chip-select lines 0 through 7 respectively.
 - cell-index : Which of multiple SPI controllers is this.
 Optional properties:
 - interrupts : Is currently not used.
@@ -23,3 +31,42 @@ Example:
 	       interrupts = <23>;
 	       status = "disabled";
        };
+
+Example with SPI direct mode support (optionally):
+	spi0: spi@10600 {
+		compatible = "marvell,orion-spi";
+		#address-cells = <1>;
+		#size-cells = <0>;
+		cell-index = <0>;
+		reg = <MBUS_ID(0xf0, 0x01) 0x10600 0x28>, /* control */
+		      <MBUS_ID(0x01, 0x1e) 0 0xffffffff>, /* CS0 */
+		      <MBUS_ID(0x01, 0x5e) 0 0xffffffff>, /* CS1 */
+		      <MBUS_ID(0x01, 0x9e) 0 0xffffffff>, /* CS2 */
+		      <MBUS_ID(0x01, 0xde) 0 0xffffffff>, /* CS3 */
+		      <MBUS_ID(0x01, 0x1f) 0 0xffffffff>, /* CS4 */
+		      <MBUS_ID(0x01, 0x5f) 0 0xffffffff>, /* CS5 */
+		      <MBUS_ID(0x01, 0x9f) 0 0xffffffff>, /* CS6 */
+		      <MBUS_ID(0x01, 0xdf) 0 0xffffffff>; /* CS7 */
+		interrupts = <23>;
+		status = "disabled";
+	};
+
+To enable the direct mode, the board specific 'ranges' property in the
+'soc' node needs to add the entries for the desired SPI controllers
+and its chip-selects that are used in the direct mode instead of PIO
+mode. Here an example for this (SPI controller 0, device 1 and SPI
+controller 1, device 2 are used in direct mode. All other SPI device
+are used in the default indirect (PIO) mode):
+	soc {
+		/*
+		 * Enable the SPI direct access by configuring an entry
+		 * here in the board-specific ranges property
+		 */
+		ranges = <MBUS_ID(0xf0, 0x01) 0 0 0xf1000000 0x100000>,	/* internal regs */
+			 <MBUS_ID(0x01, 0x1d) 0 0 0xfff00000 0x100000>,	/* BootROM       */
+			 <MBUS_ID(0x01, 0x5e) 0 0 0xf1100000 0x10000>,	/* SPI0-DEV1 */
+			 <MBUS_ID(0x01, 0x9a) 0 0 0xf1110000 0x10000>;	/* SPI1-DEV2 */
+
+For further information on the MBus bindings, please see the MBus
+DT documentation:
+Documentation/devicetree/bindings/bus/mvebu-mbus.txt