spi: add driver for J-Core SPI controller

The J-Core "spi2" device is a PIO-based SPI master controller. It
differs from "bitbang" devices in that that it's clocked in hardware
rather than via soft clock modulation over gpio, and performs
byte-at-a-time transfers between the cpu and SPI controller.

This driver will be extended to support future versions of the J-Core
SPI controller with DMA transfers when they become available.

Signed-off-by: Rich Felker <dalias@libc.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/Kconfig

@@ -285,6 +285,13 @@ config SPI_IMX
 	  This enables using the Freescale i.MX SPI controllers in master
 	  mode.
 
+config SPI_JCORE
+	tristate "J-Core SPI Master"
+	depends on OF && (SUPERH || COMPILE_TEST)
+	help
+	  This enables support for the SPI master controller in the J-Core
+	  synthesizable, open source SoC.
+
 config SPI_LM70_LLP
 	tristate "Parallel port adapter for LM70 eval board (DEVELOPMENT)"
 	depends on PARPORT

drivers/spi/Makefile

@@ -46,6 +46,7 @@ obj-$(CONFIG_SPI_FSL_SPI)		+= spi-fsl-spi.o
 obj-$(CONFIG_SPI_GPIO)			+= spi-gpio.o
 obj-$(CONFIG_SPI_IMG_SPFI)		+= spi-img-spfi.o
 obj-$(CONFIG_SPI_IMX)			+= spi-imx.o
+obj-$(CONFIG_SPI_JCORE)			+= spi-jcore.o
 obj-$(CONFIG_SPI_LM70_LLP)		+= spi-lm70llp.o
 obj-$(CONFIG_SPI_LP8841_RTC)		+= spi-lp8841-rtc.o
 obj-$(CONFIG_SPI_MESON_SPIFC)		+= spi-meson-spifc.o

drivers/spi/spi-jcore.c

@@ -0,0 +1,232 @@
+/*
+ * J-Core SPI controller driver
+ *
+ * Copyright (C) 2012-2016 Smart Energy Instruments, Inc.
+ *
+ * Current version by Rich Felker
+ * Based loosely on initial version by Oleksandr G Zhadan
+ *
+ */
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/spi/spi.h>
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/delay.h>
+
+#define DRV_NAME	"jcore_spi"
+
+#define CTRL_REG	0x0
+#define DATA_REG	0x4
+
+#define JCORE_SPI_CTRL_XMIT		0x02
+#define JCORE_SPI_STAT_BUSY		0x02
+#define JCORE_SPI_CTRL_LOOP		0x08
+#define JCORE_SPI_CTRL_CS_BITS		0x15
+
+#define JCORE_SPI_WAIT_RDY_MAX_LOOP	2000000
+
+struct jcore_spi {
+	struct spi_master *master;
+	void __iomem *base;
+	unsigned int cs_reg;
+	unsigned int speed_reg;
+	unsigned int speed_hz;
+	unsigned int clock_freq;
+};
+
+static int jcore_spi_wait(void __iomem *ctrl_reg)
+{
+	unsigned timeout = JCORE_SPI_WAIT_RDY_MAX_LOOP;
+
+	do {
+		if (!(readl(ctrl_reg) & JCORE_SPI_STAT_BUSY))
+			return 0;
+		cpu_relax();
+	} while (--timeout);
+
+	return -EBUSY;
+}
+
+static void jcore_spi_program(struct jcore_spi *hw)
+{
+	void __iomem *ctrl_reg = hw->base + CTRL_REG;
+
+	if (jcore_spi_wait(ctrl_reg))
+		dev_err(hw->master->dev.parent,
+			"timeout waiting to program ctrl reg.\n");
+
+	writel(hw->cs_reg | hw->speed_reg, ctrl_reg);
+}
+
+static void jcore_spi_chipsel(struct spi_device *spi, bool value)
+{
+	struct jcore_spi *hw = spi_master_get_devdata(spi->master);
+	u32 csbit = 1U << (2 * spi->chip_select);
+
+	dev_dbg(hw->master->dev.parent, "chipselect %d\n", spi->chip_select);
+
+	if (value)
+		hw->cs_reg |= csbit;
+	else
+		hw->cs_reg &= ~csbit;
+
+	jcore_spi_program(hw);
+}
+
+static void jcore_spi_baudrate(struct jcore_spi *hw, int speed)
+{
+	if (speed == hw->speed_hz) return;
+	hw->speed_hz = speed;
+	if (speed >= hw->clock_freq / 2)
+		hw->speed_reg = 0;
+	else
+		hw->speed_reg = ((hw->clock_freq / 2 / speed) - 1) << 27;
+	jcore_spi_program(hw);
+	dev_dbg(hw->master->dev.parent, "speed=%d reg=0x%x\n",
+		speed, hw->speed_reg);
+}
+
+static int jcore_spi_txrx(struct spi_master *master, struct spi_device *spi,
+			  struct spi_transfer *t)
+{
+	struct jcore_spi *hw = spi_master_get_devdata(master);
+
+	void __iomem *ctrl_reg = hw->base + CTRL_REG;
+	void __iomem *data_reg = hw->base + DATA_REG;
+	u32 xmit;
+
+	/* data buffers */
+	const unsigned char *tx;
+	unsigned char *rx;
+	unsigned int len;
+	unsigned int count;
+
+	jcore_spi_baudrate(hw, t->speed_hz);
+
+	xmit = hw->cs_reg | hw->speed_reg | JCORE_SPI_CTRL_XMIT;
+	tx = t->tx_buf;
+	rx = t->rx_buf;
+	len = t->len;
+
+	for (count = 0; count < len; count++) {
+		if (jcore_spi_wait(ctrl_reg))
+			break;
+
+		writel(tx ? *tx++ : 0, data_reg);
+		writel(xmit, ctrl_reg);
+
+		if (jcore_spi_wait(ctrl_reg))
+			break;
+
+		if (rx)
+			*rx++ = readl(data_reg);
+	}
+
+	spi_finalize_current_transfer(master);
+
+	if (count < len)
+		return -EREMOTEIO;
+
+	return 0;
+}
+
+static int jcore_spi_probe(struct platform_device *pdev)
+{
+	struct device_node *node = pdev->dev.of_node;
+	struct jcore_spi *hw;
+	struct spi_master *master;
+	struct resource *res;
+	u32 clock_freq;
+	struct clk *clk;
+	int err = -ENODEV;
+
+	master = spi_alloc_master(&pdev->dev, sizeof(struct jcore_spi));
+	if (!master)
+		return err;
+
+	/* Setup the master state. */
+	master->num_chipselect = 3;
+	master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH;
+	master->transfer_one = jcore_spi_txrx;
+	master->set_cs = jcore_spi_chipsel;
+	master->dev.of_node = node;
+	master->bus_num = pdev->id;
+
+	hw = spi_master_get_devdata(master);
+	hw->master = master;
+	platform_set_drvdata(pdev, hw);
+
+	/* Find and map our resources */
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res)
+		goto exit_busy;
+	if (!devm_request_mem_region(&pdev->dev, res->start,
+				     resource_size(res), pdev->name))
+		goto exit_busy;
+	hw->base = devm_ioremap_nocache(&pdev->dev, res->start,
+					resource_size(res));
+	if (!hw->base)
+		goto exit_busy;
+
+	/*
+	 * The SPI clock rate controlled via a configurable clock divider
+	 * which is applied to the reference clock. A 50 MHz reference is
+	 * most suitable for obtaining standard SPI clock rates, but some
+	 * designs may have a different reference clock, and the DT must
+	 * make the driver aware so that it can properly program the
+	 * requested rate. If the clock is omitted, 50 MHz is assumed.
+	 */
+	clock_freq = 50000000;
+	clk = devm_clk_get(&pdev->dev, "ref_clk");
+	if (!IS_ERR_OR_NULL(clk)) {
+		if (clk_enable(clk) == 0)
+			clock_freq = clk_get_rate(clk);
+		else
+			dev_warn(&pdev->dev, "could not enable ref_clk\n");
+	}
+	hw->clock_freq = clock_freq;
+
+	/* Initialize all CS bits to high. */
+	hw->cs_reg = JCORE_SPI_CTRL_CS_BITS;
+	jcore_spi_baudrate(hw, 400000);
+
+	/* Register our spi controller */
+	err = devm_spi_register_master(&pdev->dev, master);
+	if (err)
+		goto exit;
+
+	return 0;
+
+exit_busy:
+	err = -EBUSY;
+exit:
+	platform_set_drvdata(pdev, NULL);
+	spi_master_put(master);
+	return err;
+}
+
+static const struct of_device_id jcore_spi_of_match[] = {
+	{ .compatible = "jcore,spi2" },
+	{},
+};
+
+static struct platform_driver jcore_spi_driver = {
+	.probe = jcore_spi_probe,
+	.driver = {
+		.name = DRV_NAME,
+		.of_match_table = jcore_spi_of_match,
+	},
+};
+
+module_platform_driver(jcore_spi_driver);
+
+MODULE_DESCRIPTION("J-Core SPI driver");
+MODULE_AUTHOR("Rich Felker <dalias@libc.org>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:" DRV_NAME);