Message-Id: <1427819134-29128-1-git-send-email-bert@biot.com>
Date:	Tue, 31 Mar 2015 18:25:34 +0200
From:	Bert Vermeulen <bert@...t.com>
To:	ralf@...ux-mips.org, broonie@...nel.org, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	andy.shevchenko@...il.com
Cc:	Bert Vermeulen <bert@...t.com>
Subject: [PATCH v4] spi: Add SPI driver for Mikrotik RB4xx series boards

This driver mediates access between the connected CPLD and other devices
on the bus.

The m25p80-compatible boot flash and (some models) MMC use regular SPI,
bitbanged as required by the SoC. However the SPI-connected CPLD has
a "fast write" mode, in which two bits are transferred by SPI clock
cycle. The second bit is transmitted with the SoC's CS2 pin.

Protocol drivers using this fast write facility signal this by setting
the cs_change flag on transfers.

Signed-off-by: Bert Vermeulen <bert@...t.com>
---
 drivers/spi/Kconfig     |   6 ++
 drivers/spi/Makefile    |   1 +
 drivers/spi/spi-rb4xx.c | 244 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 251 insertions(+)
 create mode 100644 drivers/spi/spi-rb4xx.c

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index ab8dfbe..aa76ce5 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -429,6 +429,12 @@ config SPI_ROCKCHIP
 	  The main usecase of this controller is to use spi flash as boot
 	  device.
 
+config SPI_RB4XX
+	tristate "Mikrotik RB4XX SPI master"
+	depends on SPI_MASTER && ATH79_MACH_RB4XX
+	help
+	  SPI controller driver for the Mikrotik RB4xx series boards.
+
 config SPI_RSPI
 	tristate "Renesas RSPI/QSPI controller"
 	depends on SUPERH || ARCH_SHMOBILE || COMPILE_TEST
diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
index d8cbf65..0218f39 100644
--- a/drivers/spi/Makefile
+++ b/drivers/spi/Makefile
@@ -66,6 +66,7 @@ obj-$(CONFIG_SPI_PXA2XX)		+= spi-pxa2xx-platform.o
 obj-$(CONFIG_SPI_PXA2XX_PCI)		+= spi-pxa2xx-pci.o
 obj-$(CONFIG_SPI_QUP)			+= spi-qup.o
 obj-$(CONFIG_SPI_ROCKCHIP)		+= spi-rockchip.o
+obj-$(CONFIG_SPI_RB4XX)			+= spi-rb4xx.o
 obj-$(CONFIG_SPI_RSPI)			+= spi-rspi.o
 obj-$(CONFIG_SPI_S3C24XX)		+= spi-s3c24xx-hw.o
 spi-s3c24xx-hw-y			:= spi-s3c24xx.o
diff --git a/drivers/spi/spi-rb4xx.c b/drivers/spi/spi-rb4xx.c
new file mode 100644
index 0000000..155b81c
--- /dev/null
+++ b/drivers/spi/spi-rb4xx.c
@@ -0,0 +1,244 @@
+/*
+ * SPI controller driver for the Mikrotik RB4xx boards
+ *
+ * Copyright (C) 2010 Gabor Juhos <juhosg@...nwrt.org>
+ * Copyright (C) 2015 Bert Vermeulen <bert@...t.com>
+ *
+ * This file was based on the patches for Linux 2.6.27.39 published by
+ * MikroTik for their RouterBoard 4xx series devices.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/clk.h>
+#include <linux/spi/spi.h>
+
+#include <asm/mach-ath79/ar71xx_regs.h>
+
+#define SPI_CLOCK_FASTEST	0x40
+#define SPI_HZ			33333334
+#define CPLD_CMD_WRITE_NAND	0x08 /* bulk write mode */
+
+struct rb4xx_spi {
+	void __iomem		*base;
+	struct spi_master	*master;
+};
+
+static inline u32 rb4xx_read(struct rb4xx_spi *rbspi, u32 reg)
+{
+	return __raw_readl(rbspi->base + reg);
+}
+
+static inline void rb4xx_write(struct rb4xx_spi *rbspi, u32 reg, u32 value)
+{
+	__raw_writel(value, rbspi->base + reg);
+}
+
+static inline void do_spi_clk(struct rb4xx_spi *rbspi, u32 spi_ioc, int value)
+{
+	u32 regval;
+
+	regval = spi_ioc;
+	if (value & BIT(0))
+		regval |= AR71XX_SPI_IOC_DO;
+
+	rb4xx_write(rbspi, AR71XX_SPI_REG_IOC, regval);
+	rb4xx_write(rbspi, AR71XX_SPI_REG_IOC, regval | AR71XX_SPI_IOC_CLK);
+}
+
+static void do_spi_byte(struct rb4xx_spi *rbspi, u32 spi_ioc, u8 byte)
+{
+	int i;
+
+	for (i = 7; i >= 0; i--)
+		do_spi_clk(rbspi, spi_ioc, byte >> i);
+}
+
+static inline void do_spi_clk_fast(struct rb4xx_spi *rbspi, u32 spi_ioc,
+				   u8 value)
+{
+	u32 regval;
+
+	regval = spi_ioc;
+	if (value & BIT(1))
+		regval |= AR71XX_SPI_IOC_DO;
+	if (value & BIT(0))
+		regval |= AR71XX_SPI_IOC_CS2;
+
+	rb4xx_write(rbspi, AR71XX_SPI_REG_IOC, regval);
+	rb4xx_write(rbspi, AR71XX_SPI_REG_IOC, regval | AR71XX_SPI_IOC_CLK);
+}
+
+/* Two bits at a time, msb first */
+static void do_spi_byte_fast(struct rb4xx_spi *rbspi, u32 spi_ioc, u8 byte)
+{
+	do_spi_clk_fast(rbspi, spi_ioc, byte >> 6);
+	do_spi_clk_fast(rbspi, spi_ioc, byte >> 4);
+	do_spi_clk_fast(rbspi, spi_ioc, byte >> 2);
+	do_spi_clk_fast(rbspi, spi_ioc, byte >> 0);
+}
+
+static void rb4xx_set_cs(struct spi_device *spi, bool enable)
+{
+	struct rb4xx_spi *rbspi = spi_master_get_devdata(spi->master);
+
+	/*
+	 * Setting CS is done along with bitbanging the actual values,
+	 * since it's all on the same hardware register. However the
+	 * CPLD needs CS deselected after every command.
+	 */
+	if (!enable)
+		rb4xx_write(rbspi, AR71XX_SPI_REG_IOC,
+			    AR71XX_SPI_IOC_CS0 | AR71XX_SPI_IOC_CS1);
+}
+
+/* Deselect CS0 and CS1. */
+static int rb4xx_unprepare_transfer_hardware(struct spi_master *master)
+{
+	struct rb4xx_spi *rbspi = spi_master_get_devdata(master);
+
+	rb4xx_write(rbspi, AR71XX_SPI_REG_IOC,
+		    AR71XX_SPI_IOC_CS0 | AR71XX_SPI_IOC_CS1);
+
+	return 0;
+}
+
+static int rb4xx_transfer_one(struct spi_master *master,
+			      struct spi_device *spi, struct spi_transfer *t)
+{
+	struct rb4xx_spi *rbspi = spi_master_get_devdata(master);
+	int i;
+	u32 spi_ioc;
+	u8 *rx_buf;
+	const u8 *tx_buf;
+	unsigned char out;
+
+	/*
+	 * Prime the SPI register with the SPI device selected. The m25p80 boot
+	 * flash and CPLD share the CS0 pin. This works because the CPLD's
+	 * command set was designed to almost not clash with that of the
+	 * boot flash.
+	 */
+	if (spi->chip_select == 2)
+		spi_ioc = AR71XX_SPI_IOC_CS0;
+	else
+		spi_ioc = AR71XX_SPI_IOC_CS1;
+
+	tx_buf = t->tx_buf;
+	rx_buf = t->rx_buf;
+	for (i = 0; i < t->len; ++i) {
+		out = tx_buf ? tx_buf[i] : 0x00;
+		if (spi->chip_select == 1 && t->cs_change) {
+			/* CPLD in bulk write mode gets two bits per clock */
+			do_spi_byte_fast(rbspi, spi_ioc, out);
+			/* Don't want the real CS toggled */
+			t->cs_change = 0;
+		} else {
+			do_spi_byte(rbspi, spi_ioc, out);
+		}
+		if (!rx_buf)
+			continue;
+		rx_buf[i] = rb4xx_read(rbspi, AR71XX_SPI_REG_RDS);
+	}
+	spi_finalize_current_transfer(master);
+
+	return 0;
+}
+
+static int rb4xx_spi_setup(struct spi_device *spi)
+{
+	if (spi->mode & ~SPI_CS_HIGH) {
+		dev_err(&spi->dev, "mode %x not supported\n", spi->mode);
+		return -EINVAL;
+	}
+
+	if (spi->bits_per_word != 8 && spi->bits_per_word != 0) {
+		dev_err(&spi->dev, "bits_per_word %u not supported\n",
+			spi->bits_per_word);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int rb4xx_spi_probe(struct platform_device *pdev)
+{
+	struct spi_master *master;
+	struct clk *ahb_clk;
+	struct rb4xx_spi *rbspi;
+	struct resource *r;
+	int err;
+	void __iomem *spi_base;
+
+	ahb_clk = devm_clk_get(&pdev->dev, "ahb");
+	if (IS_ERR(ahb_clk))
+		return PTR_ERR(ahb_clk);
+
+	err = clk_prepare_enable(ahb_clk);
+	if (err)
+		return err;
+
+	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	spi_base = devm_ioremap_resource(&pdev->dev, r);
+	if (!spi_base)
+		return PTR_ERR(spi_base);
+
+	master = spi_alloc_master(&pdev->dev, sizeof(*rbspi));
+	if (!master)
+		return -ENOMEM;
+
+	master->bus_num = 0;
+	master->num_chipselect = 3;
+	master->setup = rb4xx_spi_setup;
+	master->transfer_one = rb4xx_transfer_one;
+	master->unprepare_transfer_hardware = rb4xx_unprepare_transfer_hardware;
+	master->set_cs = rb4xx_set_cs;
+
+	rbspi = spi_master_get_devdata(master);
+	rbspi->master = master;
+	rbspi->base = spi_base;
+
+	platform_set_drvdata(pdev, rbspi);
+
+	err = spi_register_master(master);
+	if (err) {
+		dev_err(&pdev->dev, "failed to register SPI master\n");
+		spi_master_put(master);
+		return err;
+	}
+
+	/* Enable SPI */
+	rb4xx_write(rbspi, AR71XX_SPI_REG_FS, AR71XX_SPI_FS_GPIO);
+
+	return 0;
+}
+
+static int rb4xx_spi_remove(struct platform_device *pdev)
+{
+	struct rb4xx_spi *rbspi = platform_get_drvdata(pdev);
+
+	spi_master_put(rbspi->master);
+
+	return 0;
+}
+
+static struct platform_driver rb4xx_spi_drv = {
+	.probe		= rb4xx_spi_probe,
+	.remove		= rb4xx_spi_remove,
+	.driver		= {
+		.name	= "rb4xx-spi",
+	},
+};
+
+module_platform_driver(rb4xx_spi_drv);
+
+MODULE_DESCRIPTION("Mikrotik RB4xx SPI controller driver");
+MODULE_AUTHOR("Gabor Juhos <juhosg@...nwrt.org>");
+MODULE_AUTHOR("Bert Vermeulen <bert@...t.com>");
+MODULE_LICENSE("GPL v2");
-- 
1.9.1

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