spi: davinci: add support for adding delay between word's transmissions

This patch adds ability to configure delay between transmission of
words over SPI bus if it's required by SPI slave devices.

New optional SPI slave property:
- ti,spi-word-delay : delay between transmission of words
	(SPIFMTn.WDELAY, SPIDAT1.WDEL)
Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-davinci.txt

 Davinci SPI controller device bindings
 
+Links on DM:
+Keystone 2 - http://www.ti.com/lit/ug/sprugp2a/sprugp2a.pdf
+dm644x - http://www.ti.com/lit/ug/sprue32a/sprue32a.pdf
+OMAP-L138/da830 - http://www.ti.com/lit/ug/spruh77a/spruh77a.pdf
+
 Required properties:
 - #address-cells: number of cells required to define a chip select
 	address on the SPI bus. Should be set to 1.
@@ -24,6 +29,30 @@ Optional:
 	cs-gpios = <0>, <0>, <0>, <&gpio1 30 0>, <&gpio1 31 0>;
 	where first three are internal CS and last two are GPIO CS.
 
+Optional properties for slave devices:
+SPI slave nodes can contain the following properties.
+Not all SPI Peripherals from Texas Instruments support this.
+Please check SPI peripheral documentation for a device before using these.
+
+- ti,spi-wdelay : delay between transmission of words
+	(SPIFMTn.WDELAY, SPIDAT1.WDEL) must be specified in number of SPI module
+	clock periods.
+
+	delay = WDELAY * SPI_module_clock_period + 2 * SPI_module_clock_period
+
+Below is timing diagram which shows functional meaning of
+"ti,spi-wdelay" parameter.
+
+             +-+ +-+ +-+ +-+ +-+                           +-+ +-+ +-+
+SPI_CLK      | | | | | | | | | |                           | | | | | |
+  +----------+ +-+ +-+ +-+ +-+ +---------------------------+ +-+ +-+ +-
+
+SPI_SOMI/SIMO+-----------------+                           +-----------
+  +----------+ word1           +---------------------------+word2
+             +-----------------+                           +-----------
+                                          WDELAY
+                                <-------------------------->
+
 Example of a NOR flash slave device (n25q032) connected to DaVinci
 SPI controller device over the SPI bus.
 
@@ -43,6 +72,7 @@ spi0:spi@20BF0000 {
 		compatible = "st,m25p32";
 		spi-max-frequency = <25000000>;
 		reg = <0>;
+		ti,spi-wdelay = <8>;
 
 		partition@0 {
 			label = "u-boot-spl";

drivers/spi/spi-davinci.c

@@ -65,6 +65,7 @@
 
 /* SPIDAT1 (upper 16 bit defines) */
 #define SPIDAT1_CSHOLD_MASK	BIT(12)
+#define SPIDAT1_WDEL		BIT(10)
 
 /* SPIGCR1 */
 #define SPIGCR1_CLKMOD_MASK	BIT(1)
@@ -209,6 +210,7 @@ static void davinci_spi_chipselect(struct spi_device *spi, int value)
 {
 	struct davinci_spi *dspi;
 	struct davinci_spi_platform_data *pdata;
+	struct davinci_spi_config *spicfg = spi->controller_data;
 	u8 chip_sel = spi->chip_select;
 	u16 spidat1 = CS_DEFAULT;
 	bool gpio_chipsel = false;
@@ -223,6 +225,10 @@ static void davinci_spi_chipselect(struct spi_device *spi, int value)
 		gpio = spi->cs_gpio;
 	}
 
+	/* program delay transfers if tx_delay is non zero */
+	if (spicfg->wdelay)
+		spidat1 |= SPIDAT1_WDEL;
+
 	/*
 	 * Board specific chip select logic decides the polarity and cs
 	 * line for the controller
@@ -237,9 +243,9 @@ static void davinci_spi_chipselect(struct spi_device *spi, int value)
 			spidat1 |= SPIDAT1_CSHOLD_MASK;
 			spidat1 &= ~(0x1 << chip_sel);
 		}
-
-		iowrite16(spidat1, dspi->base + SPIDAT1 + 2);
 	}
+
+	iowrite16(spidat1, dspi->base + SPIDAT1 + 2);
 }
 
 /**
@@ -285,7 +291,7 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
 	int prescale;
 
 	dspi = spi_master_get_devdata(spi->master);
-	spicfg = (struct davinci_spi_config *)spi->controller_data;
+	spicfg = spi->controller_data;
 	if (!spicfg)
 		spicfg = &davinci_spi_default_cfg;
 
@@ -332,6 +338,14 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
 	if (!(spi->mode & SPI_CPHA))
 		spifmt |= SPIFMT_PHASE_MASK;
 
+	/*
+	* Assume wdelay is used only on SPI peripherals that has this field
+	* in SPIFMTn register and when it's configured from board file or DT.
+	*/
+	if (spicfg->wdelay)
+		spifmt |= ((spicfg->wdelay << SPIFMT_WDELAY_SHIFT)
+				& SPIFMT_WDELAY_MASK);
+
 	/*
 	 * Version 1 hardware supports two basic SPI modes:
 	 *  - Standard SPI mode uses 4 pins, with chipselect
@@ -349,9 +363,6 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
 
 		u32 delay = 0;
 
-		spifmt |= ((spicfg->wdelay << SPIFMT_WDELAY_SHIFT)
-							& SPIFMT_WDELAY_MASK);
-
 		if (spicfg->odd_parity)
 			spifmt |= SPIFMT_ODD_PARITY_MASK;
 
@@ -383,6 +394,26 @@ static int davinci_spi_setup_transfer(struct spi_device *spi,
 	return 0;
 }
 
+static int davinci_spi_of_setup(struct spi_device *spi)
+{
+	struct davinci_spi_config *spicfg = spi->controller_data;
+	struct device_node *np = spi->dev.of_node;
+	u32 prop;
+
+	if (spicfg == NULL && np) {
+		spicfg = kzalloc(sizeof(*spicfg), GFP_KERNEL);
+		if (!spicfg)
+			return -ENOMEM;
+		*spicfg = davinci_spi_default_cfg;
+		/* override with dt configured values */
+		if (!of_property_read_u32(np, "ti,spi-wdelay", &prop))
+			spicfg->wdelay = (u8)prop;
+		spi->controller_data = spicfg;
+	}
+
+	return 0;
+}
+
 /**
  * davinci_spi_setup - This functions will set default transfer method
  * @spi: spi device on which data transfer to be done
@@ -433,7 +464,16 @@ static int davinci_spi_setup(struct spi_device *spi)
 	else
 		clear_io_bits(dspi->base + SPIGCR1, SPIGCR1_LOOPBACK_MASK);
 
-	return retval;
+	return davinci_spi_of_setup(spi);
+}
+
+static void davinci_spi_cleanup(struct spi_device *spi)
+{
+	struct davinci_spi_config *spicfg = spi->controller_data;
+
+	spi->controller_data = NULL;
+	if (spi->dev.of_node)
+		kfree(spicfg);
 }
 
 static int davinci_spi_check_error(struct davinci_spi *dspi, int int_status)
@@ -947,6 +987,7 @@ static int davinci_spi_probe(struct platform_device *pdev)
 	master->num_chipselect = pdata->num_chipselect;
 	master->bits_per_word_mask = SPI_BPW_RANGE_MASK(2, 16);
 	master->setup = davinci_spi_setup;
+	master->cleanup = davinci_spi_cleanup;
 
 	dspi->bitbang.chipselect = davinci_spi_chipselect;
 	dspi->bitbang.setup_transfer = davinci_spi_setup_transfer;