mips: spi: mscc: Add fast bitbang SPI driver

This patch add a new SPI driver for MSCC SOCs that does not sport the
designware SPI hardware controller.

Performance gain: 7.664 seconds vs. 17.633 for 1 Mbyte write.

Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>

MAINTAINERS

@@ -524,6 +524,7 @@ F:	arch/mips/dts/ocelot*
 F:	board/mscc/
 F:	configs/mscc*
 F:	drivers/gpio/mscc_sgpio.c
+F:	drivers/spi/mscc_bb_spi.c
 F:	include/configs/vcoreiii.h
 
 MIPS JZ4780

arch/mips/mach-mscc/include/mach/common.h

@@ -29,6 +29,44 @@
 
 /* Common utility functions */
 
+/*
+ * Perform a number of NOP instructions, blocks of 8 instructions.
+ * The (inlined) function will not affect cache or processor state.
+ */
+static inline void mscc_vcoreiii_nop_delay(int delay)
+{
+	while (delay > 0) {
+#define DELAY_8_NOPS() asm volatile("nop; nop; nop; nop; nop; nop; nop; nop;")
+		switch (delay) {
+		case 8:
+			DELAY_8_NOPS();
+			/* fallthrough */
+		case 7:
+			DELAY_8_NOPS();
+			/* fallthrough */
+		case 6:
+			DELAY_8_NOPS();
+			/* fallthrough */
+		case 5:
+			DELAY_8_NOPS();
+			/* fallthrough */
+		case 4:
+			DELAY_8_NOPS();
+			/* fallthrough */
+		case 3:
+			DELAY_8_NOPS();
+			/* fallthrough */
+		case 2:
+			DELAY_8_NOPS();
+			/* fallthrough */
+		case 1:
+			DELAY_8_NOPS();
+		}
+		delay -= 8;
+#undef DELAY_8_NOPS
+	}
+}
+
 int mscc_phy_rd_wr(u8 read,
 		   u32 miim_controller,
 		   u8 miim_addr,

drivers/spi/Kconfig

@@ -294,6 +294,13 @@ config SOFT_SPI
 	 Enable Soft SPI driver. This driver is to use GPIO simulate
 	 the SPI protocol.
 
+config MSCC_BB_SPI
+	bool "MSCC bitbang SPI driver"
+	depends on SOC_VCOREIII
+	help
+	  Enable MSCC bitbang SPI driver. This driver can be used on
+	  MSCC SOCs.
+
 config CF_SPI
 	bool "ColdFire SPI driver"
 	help

drivers/spi/Makefile

@@ -36,6 +36,7 @@ obj-$(CONFIG_MPC8XX_SPI) += mpc8xx_spi.o
 obj-$(CONFIG_MPC8XXX_SPI) += mpc8xxx_spi.o
 obj-$(CONFIG_MTK_QSPI) += mtk_qspi.o
 obj-$(CONFIG_MT7621_SPI) += mt7621_spi.o
+obj-$(CONFIG_MSCC_BB_SPI) += mscc_bb_spi.o
 obj-$(CONFIG_MVEBU_A3700_SPI) += mvebu_a3700_spi.o
 obj-$(CONFIG_MXC_SPI) += mxc_spi.o
 obj-$(CONFIG_MXS_SPI) += mxs_spi.o

drivers/spi/mscc_bb_spi.c

@@ -0,0 +1,236 @@
+// SPDX-License-Identifier: (GPL-2.0 OR MIT)
+/*
+ * Microsemi SoCs spi driver
+ *
+ * Copyright (c) 2018 Microsemi Corporation
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <errno.h>
+#include <malloc.h>
+#include <spi.h>
+#include <dm.h>
+#include <asm/gpio.h>
+#include <asm/io.h>
+#include <linux/delay.h>
+
+struct mscc_bb_priv {
+	void __iomem *regs;
+	u32 deactivate_delay_us;
+	bool cs_active;   /* State flag as to whether CS is asserted */
+	int cs_num;
+	u32 svalue;			/* Value to start transfer with */
+	u32 clk1;			/* Clock value start */
+	u32 clk2;			/* Clock value 2nd phase */
+};
+
+/* Delay 24 instructions for this particular application */
+#define hold_time_delay() mscc_vcoreiii_nop_delay(3)
+
+static int mscc_bb_spi_cs_activate(struct mscc_bb_priv *priv, int mode, int cs)
+{
+	if (!priv->cs_active) {
+		int cpha = mode & SPI_CPHA;
+		u32 cs_value;
+
+		priv->cs_num = cs;
+
+		if (cpha) {
+			/* Initial clock starts SCK=1 */
+			priv->clk1 = ICPU_SW_MODE_SW_SPI_SCK;
+			priv->clk2 = 0;
+		} else {
+			/* Initial clock starts SCK=0 */
+			priv->clk1 = 0;
+			priv->clk2 = ICPU_SW_MODE_SW_SPI_SCK;
+		}
+
+		/* Enable bitbang, SCK_OE, SDO_OE */
+		priv->svalue = (ICPU_SW_MODE_SW_PIN_CTRL_MODE | /* Bitbang */
+				ICPU_SW_MODE_SW_SPI_SCK_OE    | /* SCK_OE */
+				ICPU_SW_MODE_SW_SPI_SDO_OE);   /* SDO OE */
+
+		/* Add CS */
+		if (cs >= 0) {
+			cs_value =
+				ICPU_SW_MODE_SW_SPI_CS_OE(BIT(cs)) |
+				ICPU_SW_MODE_SW_SPI_CS(BIT(cs));
+		} else {
+			cs_value = 0;
+		}
+
+		priv->svalue |= cs_value;
+
+		/* Enable the CS in HW, Initial clock value */
+		writel(priv->svalue | priv->clk2, priv->regs);
+
+		priv->cs_active = true;
+		debug("Activated CS%d\n", priv->cs_num);
+	}
+
+	return 0;
+}
+
+static int mscc_bb_spi_cs_deactivate(struct mscc_bb_priv *priv, int deact_delay)
+{
+	if (priv->cs_active) {
+		/* Keep driving the CLK to its current value while
+		 * actively deselecting CS.
+		 */
+		u32 value = readl(priv->regs);
+
+		value &= ~ICPU_SW_MODE_SW_SPI_CS_M;
+		writel(value, priv->regs);
+		hold_time_delay();
+
+		/* Stop driving the clock, but keep CS with nCS == 1 */
+		value &= ~ICPU_SW_MODE_SW_SPI_SCK_OE;
+		writel(value, priv->regs);
+
+		/* Deselect hold time delay */
+		if (deact_delay)
+			udelay(deact_delay);
+
+		/* Drop everything */
+		writel(0, priv->regs);
+
+		priv->cs_active = false;
+		debug("Deactivated CS%d\n", priv->cs_num);
+	}
+
+	return 0;
+}
+
+int mscc_bb_spi_claim_bus(struct udevice *dev)
+{
+	return 0;
+}
+
+int mscc_bb_spi_release_bus(struct udevice *dev)
+{
+	return 0;
+}
+
+int mscc_bb_spi_xfer(struct udevice *dev, unsigned int bitlen,
+		     const void *dout, void *din, unsigned long flags)
+{
+	struct udevice *bus = dev_get_parent(dev);
+	struct dm_spi_slave_platdata *plat = dev_get_parent_platdata(dev);
+	struct mscc_bb_priv *priv = dev_get_priv(bus);
+	u32             i, count;
+	const u8	*txd = dout;
+	u8		*rxd = din;
+
+	debug("spi_xfer: slave %s:%s cs%d mode %d, dout %p din %p bitlen %u\n",
+	      dev->parent->name, dev->name, plat->cs,  plat->mode, dout,
+	      din, bitlen);
+
+	if (flags & SPI_XFER_BEGIN)
+		mscc_bb_spi_cs_activate(priv, plat->mode, plat->cs);
+
+	count = bitlen / 8;
+	for (i = 0; i < count; i++) {
+		u32 rx = 0, mask = 0x80, value;
+
+		while (mask) {
+			/* Initial condition: CLK is low. */
+			value = priv->svalue;
+			if (txd && txd[i] & mask)
+				value |= ICPU_SW_MODE_SW_SPI_SDO;
+
+			/* Drive data while taking CLK low. The device
+			 * we're accessing will sample on the
+			 * following rising edge and will output data
+			 * on this edge for us to be sampled at the
+			 * end of this loop.
+			 */
+			writel(value | priv->clk1, priv->regs);
+
+			/* Wait for t_setup. All devices do have a
+			 * setup-time, so we always insert some delay
+			 * here. Some devices have a very long
+			 * setup-time, which can be adjusted by the
+			 * user through vcoreiii_device->delay.
+			 */
+			hold_time_delay();
+
+			/* Drive the clock high. */
+			writel(value | priv->clk2, priv->regs);
+
+			/* Wait for t_hold. See comment about t_setup
+			 * above.
+			 */
+			hold_time_delay();
+
+			/* We sample as close to the next falling edge
+			 * as possible.
+			 */
+			value = readl(priv->regs);
+			if (value & ICPU_SW_MODE_SW_SPI_SDI)
+				rx |= mask;
+			mask >>= 1;
+		}
+		if (rxd) {
+			debug("Read 0x%02x\n", rx);
+			rxd[i] = (u8)rx;
+		}
+		debug("spi_xfer: byte %d/%d\n", i + 1, count);
+	}
+
+	debug("spi_xfer: done\n");
+
+	if (flags & SPI_XFER_END)
+		mscc_bb_spi_cs_deactivate(priv, priv->deactivate_delay_us);
+
+	return 0;
+}
+
+int mscc_bb_spi_set_speed(struct udevice *dev, unsigned int speed)
+{
+	/* Accept any speed */
+	return 0;
+}
+
+int mscc_bb_spi_set_mode(struct udevice *dev, unsigned int mode)
+{
+	return 0;
+}
+
+static const struct dm_spi_ops mscc_bb_ops = {
+	.claim_bus	= mscc_bb_spi_claim_bus,
+	.release_bus	= mscc_bb_spi_release_bus,
+	.xfer		= mscc_bb_spi_xfer,
+	.set_speed	= mscc_bb_spi_set_speed,
+	.set_mode	= mscc_bb_spi_set_mode,
+};
+
+static const struct udevice_id mscc_bb_ids[] = {
+	{ .compatible = "mscc,luton-bb-spi" },
+	{ }
+};
+
+static int mscc_bb_spi_probe(struct udevice *bus)
+{
+	struct mscc_bb_priv *priv = dev_get_priv(bus);
+
+	debug("%s: loaded, priv %p\n", __func__, priv);
+
+	priv->regs = (void __iomem *)dev_read_addr(bus);
+
+	priv->deactivate_delay_us =
+		dev_read_u32_default(bus, "spi-deactivate-delay", 0);
+
+	priv->cs_active = false;
+
+	return 0;
+}
+
+U_BOOT_DRIVER(mscc_bb) = {
+	.name	= "mscc_bb",
+	.id	= UCLASS_SPI,
+	.of_match = mscc_bb_ids,
+	.ops	= &mscc_bb_ops,
+	.priv_auto_alloc_size = sizeof(struct mscc_bb_priv),
+	.probe	= mscc_bb_spi_probe,
+};