spi: spi-pic32: Add PIC32 SPI master driver

The PIC32 SPI driver is capable of performing SPI transfers
using PIO or external DMA engine. GPIO controlled /CS support
is made default in the driver for correct operation of the
controller. This can be enabled by adding "cs-gpios" property
of the SPI node in board dts file.
Signed-off-by: Purna Chandra Mandal <purna.mandal@microchip.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/Kconfig

@@ -436,6 +436,12 @@ config SPI_ORION
 	help
 	  This enables using the SPI master controller on the Orion chips.
 
+config SPI_PIC32
+	tristate "Microchip PIC32 series SPI"
+	depends on MACH_PIC32 || COMPILE_TEST
+	help
+	  SPI driver for Microchip PIC32 SPI master controller.
+
 config SPI_PL022
 	tristate "ARM AMBA PL022 SSP controller"
 	depends on ARM_AMBA

drivers/spi/Makefile

@@ -62,6 +62,7 @@ obj-$(CONFIG_SPI_OMAP_100K)		+= spi-omap-100k.o
 obj-$(CONFIG_SPI_OMAP24XX)		+= spi-omap2-mcspi.o
 obj-$(CONFIG_SPI_TI_QSPI)		+= spi-ti-qspi.o
 obj-$(CONFIG_SPI_ORION)			+= spi-orion.o
+obj-$(CONFIG_SPI_PIC32)			+= spi-pic32.o
 obj-$(CONFIG_SPI_PL022)			+= spi-pl022.o
 obj-$(CONFIG_SPI_PPC4xx)		+= spi-ppc4xx.o
 spi-pxa2xx-platform-objs		:= spi-pxa2xx.o spi-pxa2xx-dma.o

drivers/spi/spi-pic32.c

+/*
+ * Microchip PIC32 SPI controller driver.
+ *
+ * Purna Chandra Mandal <purna.mandal@microchip.com>
+ * Copyright (c) 2016, Microchip Technology Inc.
+ *
+ * This program is free software; you can distribute it and/or modify it
+ * under the terms of the GNU General Public License (Version 2) as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+
+#include <linux/clk.h>
+#include <linux/clkdev.h>
+#include <linux/delay.h>
+#include <linux/dmaengine.h>
+#include <linux/dma-mapping.h>
+#include <linux/highmem.h>
+#include <linux/module.h>
+#include <linux/io.h>
+#include <linux/interrupt.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/of_gpio.h>
+#include <linux/of_address.h>
+#include <linux/platform_device.h>
+#include <linux/spi/spi.h>
+
+/* SPI controller registers */
+struct pic32_spi_regs {
+	u32 ctrl;
+	u32 ctrl_clr;
+	u32 ctrl_set;
+	u32 ctrl_inv;
+	u32 status;
+	u32 status_clr;
+	u32 status_set;
+	u32 status_inv;
+	u32 buf;
+	u32 dontuse[3];
+	u32 baud;
+	u32 dontuse2[3];
+	u32 ctrl2;
+	u32 ctrl2_clr;
+	u32 ctrl2_set;
+	u32 ctrl2_inv;
+};
+
+/* Bit fields of SPI Control Register */
+#define CTRL_RX_INT_SHIFT	0  /* Rx interrupt generation */
+#define  RX_FIFO_EMTPY		0
+#define  RX_FIFO_NOT_EMPTY	1 /* not empty */
+#define  RX_FIFO_HALF_FULL	2 /* full by half or more */
+#define  RX_FIFO_FULL		3 /* completely full */
+
+#define CTRL_TX_INT_SHIFT	2  /* TX interrupt generation */
+#define  TX_FIFO_ALL_EMPTY	0 /* completely empty */
+#define  TX_FIFO_EMTPY		1 /* empty */
+#define  TX_FIFO_HALF_EMPTY	2 /* empty by half or more */
+#define  TX_FIFO_NOT_FULL	3 /* atleast one empty */
+
+#define CTRL_MSTEN	BIT(5) /* enable master mode */
+#define CTRL_CKP	BIT(6) /* active low */
+#define CTRL_CKE	BIT(8) /* Tx on falling edge */
+#define CTRL_SMP	BIT(9) /* Rx at middle or end of tx */
+#define CTRL_BPW_MASK	0x03   /* bits per word/sample */
+#define CTRL_BPW_SHIFT	10
+#define  PIC32_BPW_8	0
+#define  PIC32_BPW_16	1
+#define  PIC32_BPW_32	2
+#define CTRL_SIDL	BIT(13) /* sleep when idle */
+#define CTRL_ON		BIT(15) /* enable macro */
+#define CTRL_ENHBUF	BIT(16) /* enable enhanced buffering */
+#define CTRL_MCLKSEL	BIT(23) /* select clock source */
+#define CTRL_MSSEN	BIT(28) /* macro driven /SS */
+#define CTRL_FRMEN	BIT(31) /* enable framing mode */
+
+/* Bit fields of SPI Status Register */
+#define STAT_RF_EMPTY	BIT(5) /* RX Fifo empty */
+#define STAT_RX_OV	BIT(6) /* err, s/w needs to clear */
+#define STAT_TX_UR	BIT(8) /* UR in Framed SPI modes */
+#define STAT_FRM_ERR	BIT(12) /* Multiple Frame Sync pulse */
+#define STAT_TF_LVL_MASK	0x1F
+#define STAT_TF_LVL_SHIFT	16
+#define STAT_RF_LVL_MASK	0x1F
+#define STAT_RF_LVL_SHIFT	24
+
+/* Bit fields of SPI Baud Register */
+#define BAUD_MASK		0x1ff
+
+/* Bit fields of SPI Control2 Register */
+#define CTRL2_TX_UR_EN		BIT(10) /* Enable int on Tx under-run */
+#define CTRL2_RX_OV_EN		BIT(11) /* Enable int on Rx over-run */
+#define CTRL2_FRM_ERR_EN	BIT(12) /* Enable frame err int */
+
+/* Minimum DMA transfer size */
+#define PIC32_DMA_LEN_MIN	64
+
+struct pic32_spi {
+	dma_addr_t		dma_base;
+	struct pic32_spi_regs __iomem *regs;
+	int			fault_irq;
+	int			rx_irq;
+	int			tx_irq;
+	u32			fifo_n_byte; /* FIFO depth in bytes */
+	struct clk		*clk;
+	struct spi_master	*master;
+	/* Current controller setting */
+	u32			speed_hz; /* spi-clk rate */
+	u32			mode;
+	u32			bits_per_word;
+	u32			fifo_n_elm; /* FIFO depth in words */
+#define PIC32F_DMA_PREP		0 /* DMA chnls configured */
+	unsigned long		flags;
+	/* Current transfer state */
+	struct completion	xfer_done;
+	/* PIO transfer specific */
+	const void		*tx;
+	const void		*tx_end;
+	const void		*rx;
+	const void		*rx_end;
+	int			len;
+	void (*rx_fifo)(struct pic32_spi *);
+	void (*tx_fifo)(struct pic32_spi *);
+};
+
+static inline void pic32_spi_enable(struct pic32_spi *pic32s)
+{
+	writel(CTRL_ON | CTRL_SIDL, &pic32s->regs->ctrl_set);
+}
+
+static inline void pic32_spi_disable(struct pic32_spi *pic32s)
+{
+	writel(CTRL_ON | CTRL_SIDL, &pic32s->regs->ctrl_clr);
+
+	/* avoid SPI registers read/write at immediate next CPU clock */
+	ndelay(20);
+}
+
+static void pic32_spi_set_clk_rate(struct pic32_spi *pic32s, u32 spi_ck)
+{
+	u32 div;
+
+	/* div = (clk_in / 2 * spi_ck) - 1 */
+	div = DIV_ROUND_CLOSEST(clk_get_rate(pic32s->clk), 2 * spi_ck) - 1;
+
+	writel(div & BAUD_MASK, &pic32s->regs->baud);
+}
+
+static inline u32 pic32_rx_fifo_level(struct pic32_spi *pic32s)
+{
+	u32 sr = readl(&pic32s->regs->status);
+
+	return (sr >> STAT_RF_LVL_SHIFT) & STAT_RF_LVL_MASK;
+}
+
+static inline u32 pic32_tx_fifo_level(struct pic32_spi *pic32s)
+{
+	u32 sr = readl(&pic32s->regs->status);
+
+	return (sr >> STAT_TF_LVL_SHIFT) & STAT_TF_LVL_MASK;
+}
+
+/* Return the max entries we can fill into tx fifo */
+static u32 pic32_tx_max(struct pic32_spi *pic32s, int n_bytes)
+{
+	u32 tx_left, tx_room, rxtx_gap;
+
+	tx_left = (pic32s->tx_end - pic32s->tx) / n_bytes;
+	tx_room = pic32s->fifo_n_elm - pic32_tx_fifo_level(pic32s);
+
+	/*
+	 * Another concern is about the tx/rx mismatch, we
+	 * though to use (pic32s->fifo_n_byte - rxfl - txfl) as
+	 * one maximum value for tx, but it doesn't cover the
+	 * data which is out of tx/rx fifo and inside the
+	 * shift registers. So a ctrl from sw point of
+	 * view is taken.
+	 */
+	rxtx_gap = ((pic32s->rx_end - pic32s->rx) -
+		    (pic32s->tx_end - pic32s->tx)) / n_bytes;
+	return min3(tx_left, tx_room, (u32)(pic32s->fifo_n_elm - rxtx_gap));
+}
+
+/* Return the max entries we should read out of rx fifo */
+static u32 pic32_rx_max(struct pic32_spi *pic32s, int n_bytes)
+{
+	u32 rx_left = (pic32s->rx_end - pic32s->rx) / n_bytes;
+
+	return min_t(u32, rx_left, pic32_rx_fifo_level(pic32s));
+}
+
+#define BUILD_SPI_FIFO_RW(__name, __type, __bwl)		\
+static void pic32_spi_rx_##__name(struct pic32_spi *pic32s)	\
+{								\
+	__type v;						\
+	u32 mx = pic32_rx_max(pic32s, sizeof(__type));		\
+	for (; mx; mx--) {					\
+		v = read##__bwl(&pic32s->regs->buf);		\
+		if (pic32s->rx_end - pic32s->len)		\
+			*(__type *)(pic32s->rx) = v;		\
+		pic32s->rx += sizeof(__type);			\
+	}							\
+}								\
+								\
+static void pic32_spi_tx_##__name(struct pic32_spi *pic32s)	\
+{								\
+	__type v;						\
+	u32 mx = pic32_tx_max(pic32s, sizeof(__type));		\
+	for (; mx ; mx--) {					\
+		v = (__type)~0U;				\
+		if (pic32s->tx_end - pic32s->len)		\
+			v = *(__type *)(pic32s->tx);		\
+		write##__bwl(v, &pic32s->regs->buf);		\
+		pic32s->tx += sizeof(__type);			\
+	}							\
+}
+
+BUILD_SPI_FIFO_RW(byte, u8, b);
+BUILD_SPI_FIFO_RW(word, u16, w);
+BUILD_SPI_FIFO_RW(dword, u32, l);
+
+static void pic32_err_stop(struct pic32_spi *pic32s, const char *msg)
+{
+	/* disable all interrupts */
+	disable_irq_nosync(pic32s->fault_irq);
+	disable_irq_nosync(pic32s->rx_irq);
+	disable_irq_nosync(pic32s->tx_irq);
+
+	/* Show err message and abort xfer with err */
+	dev_err(&pic32s->master->dev, "%s\n", msg);
+	if (pic32s->master->cur_msg)
+		pic32s->master->cur_msg->status = -EIO;
+	complete(&pic32s->xfer_done);
+}
+
+static irqreturn_t pic32_spi_fault_irq(int irq, void *dev_id)
+{
+	struct pic32_spi *pic32s = dev_id;
+	u32 status;
+
+	status = readl(&pic32s->regs->status);
+
+	/* Error handling */
+	if (status & (STAT_RX_OV | STAT_TX_UR)) {
+		writel(STAT_RX_OV, &pic32s->regs->status_clr);
+		writel(STAT_TX_UR, &pic32s->regs->status_clr);
+		pic32_err_stop(pic32s, "err_irq: fifo ov/ur-run\n");
+		return IRQ_HANDLED;
+	}
+
+	if (status & STAT_FRM_ERR) {
+		pic32_err_stop(pic32s, "err_irq: frame error");
+		return IRQ_HANDLED;
+	}
+
+	if (!pic32s->master->cur_msg) {
+		pic32_err_stop(pic32s, "err_irq: no mesg");
+		return IRQ_NONE;
+	}
+
+	return IRQ_NONE;
+}
+
+static irqreturn_t pic32_spi_rx_irq(int irq, void *dev_id)
+{
+	struct pic32_spi *pic32s = dev_id;
+
+	pic32s->rx_fifo(pic32s);
+
+	/* rx complete ? */
+	if (pic32s->rx_end == pic32s->rx) {
+		/* disable all interrupts */
+		disable_irq_nosync(pic32s->fault_irq);
+		disable_irq_nosync(pic32s->rx_irq);
+
+		/* complete current xfer */
+		complete(&pic32s->xfer_done);
+	}
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t pic32_spi_tx_irq(int irq, void *dev_id)
+{
+	struct pic32_spi *pic32s = dev_id;
+
+	pic32s->tx_fifo(pic32s);
+
+	/* tx complete? disable tx interrupt */
+	if (pic32s->tx_end == pic32s->tx)
+		disable_irq_nosync(pic32s->tx_irq);
+
+	return IRQ_HANDLED;
+}
+
+static void pic32_spi_dma_rx_notify(void *data)
+{
+	struct pic32_spi *pic32s = data;
+
+	complete(&pic32s->xfer_done);
+}
+
+static int pic32_spi_dma_transfer(struct pic32_spi *pic32s,
+				  struct spi_transfer *xfer)
+{
+	struct spi_master *master = pic32s->master;
+	struct dma_async_tx_descriptor *desc_rx;
+	struct dma_async_tx_descriptor *desc_tx;
+	dma_cookie_t cookie;
+	int ret;
+
+	if (!master->dma_rx || !master->dma_tx)
+		return -ENODEV;
+
+	desc_rx = dmaengine_prep_slave_sg(master->dma_rx,
+					  xfer->rx_sg.sgl,
+					  xfer->rx_sg.nents,
+					  DMA_FROM_DEVICE,
+					  DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
+	if (!desc_rx) {
+		ret = -EINVAL;
+		goto err_dma;
+	}
+
+	desc_tx = dmaengine_prep_slave_sg(master->dma_tx,
+					  xfer->tx_sg.sgl,
+					  xfer->tx_sg.nents,
+					  DMA_TO_DEVICE,
+					  DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
+	if (!desc_tx) {
+		ret = -EINVAL;
+		goto err_dma;
+	}
+
+	/* Put callback on the RX transfer, that should finish last */
+	desc_rx->callback = pic32_spi_dma_rx_notify;
+	desc_rx->callback_param = pic32s;
+
+	cookie = dmaengine_submit(desc_rx);
+	ret = dma_submit_error(cookie);
+	if (ret)
+		goto err_dma;
+
+	cookie = dmaengine_submit(desc_tx);
+	ret = dma_submit_error(cookie);
+	if (ret)
+		goto err_dma_tx;
+
+	dma_async_issue_pending(master->dma_rx);
+	dma_async_issue_pending(master->dma_tx);
+
+	return 0;
+
+err_dma_tx:
+	dmaengine_terminate_all(master->dma_rx);
+err_dma:
+	return ret;
+}
+
+static int pic32_spi_dma_config(struct pic32_spi *pic32s, u32 dma_width)
+{
+	int buf_offset = offsetof(struct pic32_spi_regs, buf);
+	struct spi_master *master = pic32s->master;
+	struct dma_slave_config cfg;
+	int ret;
+
+	cfg.device_fc = true;
+	cfg.src_addr = pic32s->dma_base + buf_offset;
+	cfg.dst_addr = pic32s->dma_base + buf_offset;
+	cfg.src_maxburst = pic32s->fifo_n_elm / 2; /* fill one-half */
+	cfg.dst_maxburst = pic32s->fifo_n_elm / 2; /* drain one-half */
+	cfg.src_addr_width = dma_width;
+	cfg.dst_addr_width = dma_width;
+	/* tx channel */
+	cfg.slave_id = pic32s->tx_irq;
+	cfg.direction = DMA_MEM_TO_DEV;
+	ret = dmaengine_slave_config(master->dma_tx, &cfg);
+	if (ret) {
+		dev_err(&master->dev, "tx channel setup failed\n");
+		return ret;
+	}
+	/* rx channel */
+	cfg.slave_id = pic32s->rx_irq;
+	cfg.direction = DMA_DEV_TO_MEM;
+	ret = dmaengine_slave_config(master->dma_rx, &cfg);
+	if (ret)
+		dev_err(&master->dev, "rx channel setup failed\n");
+
+	return ret;
+}
+
+static int pic32_spi_set_word_size(struct pic32_spi *pic32s, u8 bits_per_word)
+{
+	enum dma_slave_buswidth dmawidth;
+	u32 buswidth, v;
+
+	switch (bits_per_word) {
+	case 8:
+		pic32s->rx_fifo = pic32_spi_rx_byte;
+		pic32s->tx_fifo = pic32_spi_tx_byte;
+		buswidth = PIC32_BPW_8;
+		dmawidth = DMA_SLAVE_BUSWIDTH_1_BYTE;
+		break;
+	case 16:
+		pic32s->rx_fifo = pic32_spi_rx_word;
+		pic32s->tx_fifo = pic32_spi_tx_word;
+		buswidth = PIC32_BPW_16;
+		dmawidth = DMA_SLAVE_BUSWIDTH_2_BYTES;
+		break;
+	case 32:
+		pic32s->rx_fifo = pic32_spi_rx_dword;
+		pic32s->tx_fifo = pic32_spi_tx_dword;
+		buswidth = PIC32_BPW_32;
+		dmawidth = DMA_SLAVE_BUSWIDTH_4_BYTES;
+		break;
+	default:
+		/* not supported */
+		return -EINVAL;
+	}
+
+	/* calculate maximum number of words fifos can hold */
+	pic32s->fifo_n_elm = DIV_ROUND_UP(pic32s->fifo_n_byte,
+					  bits_per_word / 8);
+	/* set word size */
+	v = readl(&pic32s->regs->ctrl);
+	v &= ~(CTRL_BPW_MASK << CTRL_BPW_SHIFT);
+	v |= buswidth << CTRL_BPW_SHIFT;
+	writel(v, &pic32s->regs->ctrl);
+
+	/* re-configure dma width, if required */
+	if (test_bit(PIC32F_DMA_PREP, &pic32s->flags))
+		pic32_spi_dma_config(pic32s, dmawidth);
+
+	return 0;
+}
+
+static int pic32_spi_prepare_hardware(struct spi_master *master)
+{
+	struct pic32_spi *pic32s = spi_master_get_devdata(master);
+
+	pic32_spi_enable(pic32s);
+
+	return 0;
+}
+
+static int pic32_spi_prepare_message(struct spi_master *master,
+				     struct spi_message *msg)
+{
+	struct pic32_spi *pic32s = spi_master_get_devdata(master);
+	struct spi_device *spi = msg->spi;
+	u32 val;
+
+	/* set device specific bits_per_word */
+	if (pic32s->bits_per_word != spi->bits_per_word) {
+		pic32_spi_set_word_size(pic32s, spi->bits_per_word);
+		pic32s->bits_per_word = spi->bits_per_word;
+	}
+
+	/* device specific speed change */
+	if (pic32s->speed_hz != spi->max_speed_hz) {
+		pic32_spi_set_clk_rate(pic32s, spi->max_speed_hz);
+		pic32s->speed_hz = spi->max_speed_hz;
+	}
+
+	/* device specific mode change */
+	if (pic32s->mode != spi->mode) {
+		val = readl(&pic32s->regs->ctrl);
+		/* active low */
+		if (spi->mode & SPI_CPOL)
+			val |= CTRL_CKP;
+		else
+			val &= ~CTRL_CKP;
+		/* tx on rising edge */
+		if (spi->mode & SPI_CPHA)
+			val &= ~CTRL_CKE;
+		else
+			val |= CTRL_CKE;
+
+		/* rx at end of tx */
+		val |= CTRL_SMP;
+		writel(val, &pic32s->regs->ctrl);
+		pic32s->mode = spi->mode;
+	}
+
+	return 0;
+}
+
+static bool pic32_spi_can_dma(struct spi_master *master,
+			      struct spi_device *spi,
+			      struct spi_transfer *xfer)
+{
+	struct pic32_spi *pic32s = spi_master_get_devdata(master);
+
+	/* skip using DMA on small size transfer to avoid overhead.*/
+	return (xfer->len >= PIC32_DMA_LEN_MIN) &&
+	       test_bit(PIC32F_DMA_PREP, &pic32s->flags);
+}
+
+static int pic32_spi_one_transfer(struct spi_master *master,
+				  struct spi_device *spi,
+				  struct spi_transfer *transfer)
+{
+	struct pic32_spi *pic32s;
+	bool dma_issued = false;
+	int ret;
+
+	pic32s = spi_master_get_devdata(master);
+
+	/* handle transfer specific word size change */
+	if (transfer->bits_per_word &&
+	    (transfer->bits_per_word != pic32s->bits_per_word)) {
+		ret = pic32_spi_set_word_size(pic32s, transfer->bits_per_word);
+		if (ret)
+			return ret;
+		pic32s->bits_per_word = transfer->bits_per_word;
+	}
+
+	/* handle transfer specific speed change */
+	if (transfer->speed_hz && (transfer->speed_hz != pic32s->speed_hz)) {
+		pic32_spi_set_clk_rate(pic32s, transfer->speed_hz);
+		pic32s->speed_hz = transfer->speed_hz;
+	}
+
+	reinit_completion(&pic32s->xfer_done);
+
+	/* transact by DMA mode */
+	if (transfer->rx_sg.nents && transfer->tx_sg.nents) {
+		ret = pic32_spi_dma_transfer(pic32s, transfer);
+		if (ret) {
+			dev_err(&spi->dev, "dma submit error\n");
+			return ret;
+		}
+
+		/* DMA issued */
+		dma_issued = true;
+	} else {
+		/* set current transfer information */
+		pic32s->tx = (const void *)transfer->tx_buf;
+		pic32s->rx = (const void *)transfer->rx_buf;
+		pic32s->tx_end = pic32s->tx + transfer->len;
+		pic32s->rx_end = pic32s->rx + transfer->len;
+		pic32s->len = transfer->len;
+
+		/* transact by interrupt driven PIO */
+		enable_irq(pic32s->fault_irq);
+		enable_irq(pic32s->rx_irq);
+		enable_irq(pic32s->tx_irq);
+	}
+
+	/* wait for completion */
+	ret = wait_for_completion_timeout(&pic32s->xfer_done, 2 * HZ);
+	if (ret <= 0) {
+		dev_err(&spi->dev, "wait error/timedout\n");
+		if (dma_issued) {
+			dmaengine_terminate_all(master->dma_rx);
+			dmaengine_terminate_all(master->dma_rx);
+		}
+		ret = -ETIMEDOUT;
+	} else {
+		ret = 0;
+	}
+
+	return ret;
+}
+
+static int pic32_spi_unprepare_message(struct spi_master *master,
+				       struct spi_message *msg)
+{
+	/* nothing to do */
+	return 0;
+}
+
+static int pic32_spi_unprepare_hardware(struct spi_master *master)
+{
+	struct pic32_spi *pic32s = spi_master_get_devdata(master);
+
+	pic32_spi_disable(pic32s);
+
+	return 0;
+}
+
+/* This may be called multiple times by same spi dev */
+static int pic32_spi_setup(struct spi_device *spi)
+{
+	if (!spi->max_speed_hz) {
+		dev_err(&spi->dev, "No max speed HZ parameter\n");
+		return -EINVAL;
+	}
+
+	switch (spi->bits_per_word) {
+	case 8:
+	case 16:
+	case 32:
+		break;
+	default:
+		dev_err(&spi->dev, "Invalid bits_per_word defined\n");
+		return -EINVAL;
+	}
+
+	/* PIC32 spi controller can drive /CS during transfer depending
+	 * on tx fifo fill-level. /CS will stay asserted as long as TX
+	 * fifo is non-empty, else will be deasserted indicating
+	 * completion of the ongoing transfer. This might result into
+	 * unreliable/erroneous SPI transactions.
+	 * To avoid that we will always handle /CS by toggling GPIO.
+	 */
+	if (!gpio_is_valid(spi->cs_gpio))
+		return -EINVAL;
+
+	gpio_direction_output(spi->cs_gpio, !(spi->mode & SPI_CS_HIGH));
+
+	return 0;
+}
+
+static void pic32_spi_cleanup(struct spi_device *spi)
+{
+	/* de-activate cs-gpio */
+	gpio_direction_output(spi->cs_gpio, !(spi->mode & SPI_CS_HIGH));
+}
+
+static void pic32_spi_dma_prep(struct pic32_spi *pic32s, struct device *dev)
+{
+	struct spi_master *master = pic32s->master;
+	dma_cap_mask_t mask;
+
+	dma_cap_zero(mask);
+	dma_cap_set(DMA_SLAVE, mask);
+
+	master->dma_rx = dma_request_slave_channel_compat(mask, NULL, NULL,
+							  dev, "spi-rx");
+	if (!master->dma_rx) {
+		dev_warn(dev, "RX channel not found.\n");
+		goto out_err;
+	}
+
+	master->dma_tx = dma_request_slave_channel_compat(mask, NULL, NULL,
+							  dev, "spi-tx");
+	if (!master->dma_tx) {
+		dev_warn(dev, "TX channel not found.\n");
+		goto out_err;
+	}
+
+	if (pic32_spi_dma_config(pic32s, DMA_SLAVE_BUSWIDTH_1_BYTE))
+		goto out_err;
+
+	/* DMA chnls allocated and prepared */
+	set_bit(PIC32F_DMA_PREP, &pic32s->flags);
+
+	return;
+
+out_err:
+	if (master->dma_rx)
+		dma_release_channel(master->dma_rx);
+
+	if (master->dma_tx)
+		dma_release_channel(master->dma_tx);
+}
+
+static void pic32_spi_dma_unprep(struct pic32_spi *pic32s)
+{
+	if (!test_bit(PIC32F_DMA_PREP, &pic32s->flags))
+		return;
+
+	clear_bit(PIC32F_DMA_PREP, &pic32s->flags);
+	if (pic32s->master->dma_rx)
+		dma_release_channel(pic32s->master->dma_rx);
+
+	if (pic32s->master->dma_tx)
+		dma_release_channel(pic32s->master->dma_tx);
+}
+
+static void pic32_spi_hw_init(struct pic32_spi *pic32s)
+{
+	u32 ctrl;
+
+	/* disable hardware */
+	pic32_spi_disable(pic32s);
+
+	ctrl = readl(&pic32s->regs->ctrl);
+	/* enable enhanced fifo of 128bit deep */
+	ctrl |= CTRL_ENHBUF;
+	pic32s->fifo_n_byte = 16;
+
+	/* disable framing mode */
+	ctrl &= ~CTRL_FRMEN;
+
+	/* enable master mode while disabled */
+	ctrl |= CTRL_MSTEN;
+
+	/* set tx fifo threshold interrupt */
+	ctrl &= ~(0x3 << CTRL_TX_INT_SHIFT);
+	ctrl |= (TX_FIFO_HALF_EMPTY << CTRL_TX_INT_SHIFT);
+
+	/* set rx fifo threshold interrupt */
+	ctrl &= ~(0x3 << CTRL_RX_INT_SHIFT);
+	ctrl |= (RX_FIFO_NOT_EMPTY << CTRL_RX_INT_SHIFT);
+
+	/* select clk source */
+	ctrl &= ~CTRL_MCLKSEL;
+
+	/* set manual /CS mode */
+	ctrl &= ~CTRL_MSSEN;
+
+	writel(ctrl, &pic32s->regs->ctrl);
+
+	/* enable error reporting */
+	ctrl = CTRL2_TX_UR_EN | CTRL2_RX_OV_EN | CTRL2_FRM_ERR_EN;
+	writel(ctrl, &pic32s->regs->ctrl2_set);
+}
+
+static int pic32_spi_hw_probe(struct platform_device *pdev,
+			      struct pic32_spi *pic32s)
+{
+	struct resource *mem;
+	int ret;
+
+	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	pic32s->regs = devm_ioremap_resource(&pdev->dev, mem);
+	if (!pic32s->regs) {
+		dev_err(&pdev->dev, "ioremap() failed\n");
+		return -ENOMEM;
+	}
+	pic32s->dma_base = mem->start;
+
+	/* get irq resources: err-irq, rx-irq, tx-irq */
+	pic32s->fault_irq = platform_get_irq_byname(pdev, "fault");
+	if (pic32s->fault_irq < 0) {
+		dev_err(&pdev->dev, "fault-irq not found\n");
+		return pic32s->fault_irq;
+	}
+
+	pic32s->rx_irq = platform_get_irq_byname(pdev, "rx");
+	if (pic32s->rx_irq < 0) {
+		dev_err(&pdev->dev, "rx-irq not found\n");
+		return pic32s->rx_irq;
+	}
+
+	pic32s->tx_irq = platform_get_irq_byname(pdev, "tx");
+	if (pic32s->tx_irq < 0) {
+		dev_err(&pdev->dev, "tx-irq not found\n");
+		return pic32s->tx_irq;
+	}
+
+	/* get clock */
+	pic32s->clk = devm_clk_get(&pdev->dev, "mck0");
+	if (IS_ERR(pic32s->clk)) {
+		dev_err(&pdev->dev, "clk not found\n");
+		ret = PTR_ERR(pic32s->clk);
+		goto err_unmap_mem;
+	}
+
+	ret = clk_prepare_enable(pic32s->clk);
+	if (ret)
+		goto err_unmap_mem;
+
+	pic32_spi_hw_init(pic32s);
+
+	return 0;
+
+err_unmap_mem:
+	dev_err(&pdev->dev, "%s failed, err %d\n", __func__, ret);
+	return ret;
+}
+
+static int pic32_spi_probe(struct platform_device *pdev)
+{
+	struct spi_master *master;
+	struct pic32_spi *pic32s;
+	int ret;
+
+	master = spi_alloc_master(&pdev->dev, sizeof(*pic32s));
+	if (!master)
+		return -ENOMEM;
+
+	pic32s = spi_master_get_devdata(master);
+	pic32s->master = master;
+
+	ret = pic32_spi_hw_probe(pdev, pic32s);
+	if (ret)
+		goto err_master;
+
+	master->dev.of_node	= of_node_get(pdev->dev.of_node);
+	master->mode_bits	= SPI_MODE_3 | SPI_MODE_0 | SPI_CS_HIGH;
+	master->num_chipselect	= 1; /* single chip-select */
+	master->max_speed_hz	= clk_get_rate(pic32s->clk);
+	master->setup		= pic32_spi_setup;
+	master->cleanup		= pic32_spi_cleanup;
+	master->flags		= SPI_MASTER_MUST_TX | SPI_MASTER_MUST_RX;
+	master->bits_per_word_mask	= SPI_BPW_RANGE_MASK(8, 32);
+	master->transfer_one		= pic32_spi_one_transfer;
+	master->prepare_message		= pic32_spi_prepare_message;
+	master->unprepare_message	= pic32_spi_unprepare_message;
+	master->prepare_transfer_hardware	= pic32_spi_prepare_hardware;
+	master->unprepare_transfer_hardware	= pic32_spi_unprepare_hardware;
+
+	/* optional DMA support */
+	pic32_spi_dma_prep(pic32s, &pdev->dev);
+	if (test_bit(PIC32F_DMA_PREP, &pic32s->flags))
+		master->can_dma	= pic32_spi_can_dma;
+
+	init_completion(&pic32s->xfer_done);
+	pic32s->mode = -1;
+
+	/* install irq handlers (with irq-disabled) */
+	irq_set_status_flags(pic32s->fault_irq, IRQ_NOAUTOEN);
+	ret = devm_request_irq(&pdev->dev, pic32s->fault_irq,
+			       pic32_spi_fault_irq, IRQF_NO_THREAD,
+			       dev_name(&pdev->dev), pic32s);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "request fault-irq %d\n", pic32s->rx_irq);
+		goto err_bailout;
+	}
+
+	/* receive interrupt handler */
+	irq_set_status_flags(pic32s->rx_irq, IRQ_NOAUTOEN);
+	ret = devm_request_irq(&pdev->dev, pic32s->rx_irq,
+			       pic32_spi_rx_irq, IRQF_NO_THREAD,
+			       dev_name(&pdev->dev), pic32s);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "request rx-irq %d\n", pic32s->rx_irq);
+		goto err_bailout;
+	}
+
+	/* transmit interrupt handler */
+	irq_set_status_flags(pic32s->tx_irq, IRQ_NOAUTOEN);
+	ret = devm_request_irq(&pdev->dev, pic32s->tx_irq,
+			       pic32_spi_tx_irq, IRQF_NO_THREAD,
+			       dev_name(&pdev->dev), pic32s);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "request tx-irq %d\n", pic32s->tx_irq);
+		goto err_bailout;
+	}
+
+	/* register master */
+	ret = devm_spi_register_master(&pdev->dev, master);
+	if (ret) {
+		dev_err(&master->dev, "failed registering spi master\n");
+		goto err_bailout;
+	}
+
+	platform_set_drvdata(pdev, pic32s);
+
+	return 0;
+
+err_bailout:
+	clk_disable_unprepare(pic32s->clk);
+err_master:
+	spi_master_put(master);
+	return ret;
+}
+
+static int pic32_spi_remove(struct platform_device *pdev)
+{
+	struct pic32_spi *pic32s;
+
+	pic32s = platform_get_drvdata(pdev);
+	pic32_spi_disable(pic32s);
+	clk_disable_unprepare(pic32s->clk);
+	pic32_spi_dma_unprep(pic32s);
+
+	return 0;
+}
+
+static const struct of_device_id pic32_spi_of_match[] = {
+	{.compatible = "microchip,pic32mzda-spi",},
+	{},
+};
+MODULE_DEVICE_TABLE(of, pic32_spi_of_match);
+
+static struct platform_driver pic32_spi_driver = {
+	.driver = {
+		.name = "spi-pic32",
+		.of_match_table = of_match_ptr(pic32_spi_of_match),
+	},
+	.probe = pic32_spi_probe,
+	.remove = pic32_spi_remove,
+};
+
+module_platform_driver(pic32_spi_driver);
+
+MODULE_AUTHOR("Purna Chandra Mandal <purna.mandal@microchip.com>");
+MODULE_DESCRIPTION("Microchip SPI driver for PIC32 SPI controller.");
+MODULE_LICENSE("GPL v2");